Enzyme replacement therapy for mucopolysaccharidosis VI: a phase 3, randomized, double-blind, placebo-controlled, multinational study of recombinant human N-acetylgalactosamine 4-sulfatase (recombinant human arylsulfatase B or rhASB) and follow-on, open-label extension study

Humanistic burden of mucopolysaccharidoses: a systematic literature review

OBJECTIVE

To systematically review the literature and summarize the health-related quality-of-life (HRQoL) of patients undergoing treatment for mucopolysaccharidoses (MPS), a rare, hereditary lysosomal storage disorder.

METHODS

A systematic review was performed in accordance with PRISMA guidelines to identify research studies that describe the humanistic burden of MPS. A comprehensive literature search was conducted in EMBASE, MEDLINE, and eligible conferences were screened to include applicable abstracts.

RESULTS

Of 870 identified articles, 15 studies reported the HRQoL burden of patients with MPS undergoing or with a history of ERT and/or HSCT. These studies include patients of MPS I (n = 2), MPS II (n = 4), MPS IV (n = 6), MPS VI (n = 1), and subtype not mentioned (n = 2). Although the quality-of-life of MPS patients is influenced by time of diagnosis, pain, cognitive involvement, severity of disease, mobility, dependence, and time of treatment initiation, the HRQoL scores of MPS patients across all the scales were below the median reference population scores across all dimensions. This is seen in comparison to healthy participants but also in comparison to patients with other chronic illnesses. The multi-organ involvement, neurological impairment, pain, and morbidity associated with the condition not only affects activity of daily living but also affects social functioning, emotional status, employment status among adults, and school functioning among children.

CONCLUSIONS

This systematic literature review revealed the substantial humanistic burden of individuals affected by MPS as well as caregivers. Significant variation in HRQoL scores was observed, however studies indicate that the quality-of-life of MPS patients is influenced primarily by severity of disease (MPS type and phenotype), and then by time of diagnosis, pain, cognitive involvement, mobility, dependence, and time of treatment initiation. Further studies are needed to assess the global humanistic burden of MPS, particularly in MPS III, VI, VII, and IX subtypes, in adults, and for a longer follow-up period. Considering the vast array of HRQoL assessment tools available and used in this study, researchers should also consider using scales with condition-specific measures to ensure appropriate estimates of effectiveness.

Biomarkers of Glycosaminoglycans (GAG) accumulation in patients with mucopolysaccharidosis type VI-LeukoGAG, Corneal Opacification (COM) and Carotid Intima Media Thickening (CIMT)

Mucopolysaccharidosis type VI (MPS VI) is an autosomal recessive lysosomal storage disorder characterized by deficient activity of arylsulfatase B enzyme (ASB) resulting in cellular accumulation of dermatan sulfate (DS) and chondroitin sulfate (CS) that leads to cell injury. Urinary glycosaminoglycans (GAG) are often used as a biomarker in MPS diseases for diagnosis and to monitor treatment efficacy. This study evaluated leukocyte GAGs (leukoGAG) and skin GAGs as alternate biomarkers representing intracellular GAG changes in patients with MPS VI and treated with enzyme replacement therapy (ERT). In addition, we evaluated corneal opacification measurements (COM) and carotid intima media thickness (CIMT) as indicators of GAG accumulation and tissue injury. The study was performed in a serial two-step design in a single center. A quantitative method to measure leukoGAG levels in leukocytes was developed in Study 1 to compare the GAG levels between MPS VI patients and a control group and to assess correlations between leukoGAG and urineGAG. Study 2 validated the leukoGAG measurement, assessed the effect of ERT infusion on leukoGAG and ASB activity in leukocytes, identified correlations between leukoGAG and other biomarkers, and assessed differences in GAG accumulation between MPS VI patients and control subjects. In Study 1, leukoCS and leukoDS levels were significantly higher in the MPS VI group than the control group (leukoCS: 37.9 ± 10.2 and 2.9 ± 1.5 μg/μg protein, respectively, p = 0.005; leukoDS: 0.26 ± 0.2 and 0.0 ± 0.0 μg/μg protein, respectively, p = 0.028) with positive correlations between leukoCS and urine CS and leukoDS and urineDS. In Study 2, leukoCS (32.0 ± 11.8 vs 6.9 ± 3.1 μg/mg protein, p = 0.005) and leukoDS (0.4 ± 0.1 and 0.2 ± 0.1 μg/mg protein, p = 0.020) were significantly higher compared with control subjects. Thus, these results highlight the potential of leukoGAG as a new biomarker representing intracellular GAG accumulation in MPS VI patients and may be valuable for patient management.

An immune deficient mouse model for mucopolysaccharidosis IIIA (Sanfilippo syndrome)

Mucopolysaccharidosis III (MPSIII, Sanfilippo syndrome) is a devastating lysosomal storage disease that primarily affects the central nervous system. MPSIIIA is caused by loss-of-function mutations in the gene coding for sulfamidase (N-sulfoglucosamine sulfohydrolase/SGSH) resulting in SGSH enzyme deficiency, a buildup of heparin sulfate and subsequent neurodegeneration. There is currently no cure or disease modifying treatment for MPSIIIA. A mouse model for MPSIIIA was characterized in 1999 and later backcrossed onto the C57BL/6 background. In the present study, a novel immune deficient MPSIIIA mouse model (MPSIIIA-TKO) was created by backcrossing the immune competent, C57BL/6 MPSIIIA mouse to an immune deficient mouse model lacking Rag2, CD47 and Il2rg genes. The resulting mouse model has undetectable SGSH activity, exhibits histological changes consistent with MPSIIIA and lacks T cells, B cells and NK cells. This new mouse model has the potential to be extremely useful in testing human cellular therapies in an animal model as it retains the MPSIIIA disease phenotype while tolerating xenotransplantation.

Glycosylation shapes the efficacy and safety of diverse protein, gene and cell therapies

Over recent decades, therapeutic proteins have had widespread success in treating a myriad of diseases. Glycosylation, a near universal feature of this class of drugs, is a critical quality attribute that significantly influences the physical properties, safety profile and biological activity of therapeutic proteins. Optimizing protein glycosylation, therefore, offers an important avenue to developing more efficacious therapies. In this review, we discuss specific examples of how variations in glycan structure and glycoengineering impacts the stability, safety, and clinical efficacy of protein-based drugs that are already in the market as well as those that are still in preclinical development. We also highlight the impact of glycosylation on next generation biologics such as T cell-based cancer therapy and gene therapy.

Early enzyme replacement therapy prevents dental and craniofacial abnormalities in a mouse model of mucopolysaccharidosis type VI

Mucopolysaccharidosis VI (MPS VI) is a hereditary lysosomal storage disease caused by the absence of the enzyme arylsulfatase B (ARSB). Craniofacial defects are common in MPS VI patients and manifest as abnormalities of the facial bones, teeth, and temporomandibular joints. Although enzyme replacement therapy (ERT) is the treatment of choice for MPS VI, the effects on the craniofacial and dental structures are still poorly understood. In this study, we used an Arsb-deficient mouse model (Arsbm/m) that mimics MPS VI to investigate the effects of ERT on dental and craniofacial structures and compared these results with clinical and radiological observations from three MPS VI patients. Using micro-computed tomography, we found that the craniofacial phenotype of the Arsbm/m mice was characterized by bone exostoses at the insertion points of the masseter muscles and an overall increased volume of the jaw bone. An early start of ERT (at 4 weeks of age for 20 weeks) resulted in a moderate improvement of these jaw anomalies, while a late start of ERT (at 12 weeks of age for 12 weeks) showed no effect on the craniofacial skeleton. While teeth typically developed in Arsbm/m mice, we observed a pronounced loss of tooth-bearing alveolar bone. This alveolar bone loss, which has not been described before in MPS VI, was also observed in one of the MPS VI patients. Interestingly, only an early start of ERT led to a complete normalization of the alveolar bone in Arsbm/m mice. The temporomandibular joints in Arsbm/m mice were deformed and had a porous articular surface. Histological analysis revealed a loss of physiological cartilage layering, which was also reflected in an altered proteoglycan content in the cartilage of Arsbm/m mice. These abnormalities could only be partially corrected by an early start of ERT. In conclusion, our results show that an early start of ERT in Arsbm/m mice achieves the best therapeutic effects for tooth, bone, and temporomandibular joint development. As the MPS VI mouse model in this study resembles the clinical findings in MPS VI patients, our results suggest enzyme replacement therapy should be started as early as possible.

Generation of a novel disease model mouse for mucopolysaccharidosis type VI via c. 252T>C human ARSB mutation knock-in

Mucopolysaccharidosis type VI (MPS VI) is an autosomal recessive lysosomal disorder caused by a mutation in the ARSB gene, which encodes arylsulfatase B (ARSB), and is characterized by glycosaminoglycan accumulation. Some pathogenic mutations have been identified in or near the substrate-binding pocket of ARSB, whereas many missense mutations present far from the substrate-binding pocket. Each MPS VI patient shows different severity of clinical symptoms. To understand the relationship between mutation patterns and the severity of MPS VI clinical symptoms, mutations located far from the substrate-binding pocket must be investigated using mutation knock-in mice. Here, I generated a knock-in mouse model of human ARSB Y85H mutation identified in Japanese MPS VI patients using a CRISPR-Cas9-mediated approach. The generated mouse model exhibited phenotypes similar to those of MPS VI patients, including facial features, mucopolysaccharide accumulation, and smaller body size, suggesting that this mouse will be a valuable model for understanding MPS VI pathology.

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We generated a mouse model of the Y85H ARSB mutation in humans using CRISPR-Cas9.

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The knock-in mice exhibited phenotypes similar to those of MPS VI patients.

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The mice showed facial features, mucopolysaccharide build-up, and smaller bodies.

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The model could successfully show the correlation between genotype and phenotype.

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These mice could serve as a useful model for novel therapeutic approaches.

Exosome- and extracellular vesicle-based approaches for the treatment of lysosomal storage disorders

Cell-generated extracellular vesicles (EVs) are being engineered as biologically-inspired vehicles for targeted delivery of therapeutic agents to treat difficult-to-manage human diseases, including lysosomal storage disorders (LSDs). Engineered EVs offer distinct advantages for targeted delivery of therapeutics compared to existing synthetic and semi-synthetic nanoscale systems, for example with regard to their biocompatibility, circulation lifetime, efficiencies in delivery of drugs and biologics to target cells, and clearance from the body. Here, we review literature related to the design and preparation of EVs as therapeutic carriers for targeted delivery and therapy of drugs and biologics with a focus on LSDs. First, we introduce the basic pathophysiology of LDSs and summarize current approaches to diagnose and treat LSDs. Second, we will provide specific details about EVs, including subtypes, biogenesis, biological properties and their potential to treat LSDs. Third, we review state-of-the-art approaches to engineer EVs for treatments of LSDs. Finally, we summarize explorative basic research and applied applications of engineered EVs for LSDs, and highlight current challenges, and new directions in developing EV-based therapies and their potential impact on clinical medicine.

Long-term efficacy and safety of vestronidase alfa enzyme replacement therapy in pediatric subjects < 5 years with mucopolysaccharidosis VII

Mucopolysaccharidosis (MPS) VII is an ultra-rare, autosomal-recessive, metabolic disease caused by a deficiency of β-glucuronidase, a lysosomal enzyme that hydrolyzes glycosaminoglycans (GAGs), including dermatan sulfate (DS), chondroitin sulfate, and heparan sulfate (HS). β-glucuronidase deficiency leads to progressive accumulation of undegraded GAGs in lysosomes of affected tissues, which may cause hydrops fetalis, short stature, hepatosplenomegaly, and cognitive impairment. An open-label, multicenter, phase II study was conducted in 8 pediatric subjects <5 years of age with MPS VII. Subjects received the recombinant human β-glucuronidase vestronidase alfa 4 mg/kg by intravenous infusion every other week for 48 weeks (treatment period). Those who completed the 48-week treatment were offered to continue treatment with vestronidase alfa 4 mg/kg for up to 240 weeks or until withdrawal of consent, discontinuation, or study termination (continuation period). The level of GAG excreted in urine (uGAG) above normal has been shown to correlate with disease severity and clinical outcomes in MPS diseases. Therefore, the primary efficacy endpoint of this study was to determine the mean percentage change in uGAG DS excretion from baseline to week 48. Statistically significant reductions in uGAG DS from baseline were observed at each visit (p < 0.0001), with a least square mean (standard error) percentage change of -60% (6.6) at week 4 (first post-baseline assessment) and -61% (6.41) at week 48 (final assessment during treatment period). Secondary efficacy endpoints included change from baseline to week 48 in growth and hepatosplenomegaly. Positive trends were observed toward increased standing height Z-score (mean [standard deviation] at baseline, -2.630 [1.17], n = 8; at week 48, -2.045 [0.27], n = 7) and growth velocity (mean [SD] Z-score at baseline, -2.59 [1.49], n = 4; at week 48, -0.39 [2.10], n = 4; p = 0.27). Hepatomegaly was resolved in 3 of 3 subjects assessed by ultrasound and in 5 of 6 subjects assessed by physical examination; splenomegaly was resolved in 1 of 3 subjects assessed by ultrasound and in 2 of 2 subjects assessed by physical examination. There were no new safety signals identified during this study. Mild-to-moderate infusion-associated reactions occurred in 4 (50%) subjects. In conclusion, long-term vestronidase alfa treatment demonstrated a rapid and sustained reduction in uGAGs, maintained growth, and improved hepatosplenomegaly in pediatric subjects with MPS VII <5 years of age. Trial registration: NCT02418455.

Oral treatment for mucopolysaccharidosis VI: Outcomes of the first phase IIa study with odiparcil

Mucopolysaccharidosis (MPS) disorders are a group of rare, progressive lysosomal storage diseases characterized by the accumulation of glycosaminoglycans (GAGs) and classified according to the deficient enzyme. Enzyme replacement therapy (ERT) of MPS VI has limited effects on ophthalmic, cardiovascular, and skeletal systems. Odiparcil is an orally available small molecule that results in the synthesis of odiparcil-linked GAGs facilitating their excretion and reducing cellular and tissue GAG accumulation. Improve MPS treatment was a Phase 2a study of the safety, pharmacokinetics/pharmacodynamics, and efficacy of two doses of odiparcil in patients with MPS VI. The core study was a 26-week, randomized, double-blind, placebo-controlled trial in patients receiving ERT and an open-label, noncomparative, single-dose cohort not receiving ERT. Patients aged ≥ 16 years receiving ERT were randomized to odiparcil 250 or 500 mg twice daily or placebo. Patients without ERT received odiparcil 500 mg twice daily. Of 20 patients enrolled, 13 (65.0%) completed the study. Odiparcil increased total urine GAGs (uGAGs), chondroitin sulfate, and dermatan sulfate concentrations. A linear increase in uGAG levels and odiparcil exposure occurred with increased odiparcil dose. Odiparcil demonstrated a good safety and tolerability profile. Individual analyses found more improvements in pain, corneal clouding, cardiac, vascular, and respiratory functions in the odiparcil groups vs placebo. This study confirmed the mechanism of action and established the safety of odiparcil with clinical beneficial effects after only a short treatment duration in an advanced stage of disease. Further assessment of odiparcil in younger patients is needed.

Surgical Management of Valvular Heart Disease in Mucopolysaccharidoses: A Review of Literature

Mucopolysaccharidoses are extremely rare diseases that are frequently presenting with structural heart problems of the aortic and mitral valve in combination with myocardial dysfunction. In a substantial proportion, this leads to heart failure and is a leading cause of death in these patients. As this glycosaminoglycan degradation defect is associated with other conditions strongly influencing the perioperative risk and choice of surgical technique, multidisciplinary planning is crucial to improve short- and long-term outcomes. The extensive variance in clinical presentation between different impaired enzymes, and further within subgroups, calls for personalised treatment plans. Enzyme replacement therapies and bone marrow transplantation carry great potential as they may significantly abrogate the progress of the disease and as such reduce the clinical burden and improve life expectancy. Nevertheless, structural heart interventions may be required. We reviewed the existing literature of the less than 50 published cases regarding surgical management, technique, and choice of prostheses. Although improvement in therapy has shown promising results in protecting valvar tissue when initiated in infancy, concerns regarding stability of this effect and durability of biological prostheses remain.

Mucopolysaccharidosis Type VI, an Updated Overview of the Disease

Mucopolysaccharidosis type VI, or Maroteaux-Lamy syndrome, is a rare, autosomal recessive genetic disease, mainly affecting the pediatric age group. The disease is due to pathogenic variants of the ARSB gene, coding for the lysosomal hydrolase N-acetylgalactosamine 4-sulfatase (arylsulfatase B, ASB). The enzyme deficit causes a pathological accumulation of the undegraded glycosaminoglycans dermatan-sulphate and chondroitin-sulphate, natural substrates of ASB activity. Intracellular and extracellular deposits progressively take to a pathological scenario, often severe, involving most organ-systems and generally starting from the osteoarticular apparatus. Neurocognitive and behavioral abilities, commonly described as maintained, have been actually investigated by few studies. The disease, first described in 1963, has a reported prevalence between 0.36 and 1.3 per 100,000 live births across the continents. With this paper, we wish to contribute an updated overview of the disease from the clinical, diagnostic, and therapeutic sides. The numerous in vitro and in vivo preclinical studies conducted in the last 10-15 years to dissect the disease pathogenesis, the efficacy of the available therapeutic treatment (enzyme replacement therapy), as well as new therapies under study are here described. This review also highlights the need to identify new disease biomarkers, potentially speeding up the diagnostic process and the monitoring of therapeutic efficacy.

Clinical and event-based outcomes of patients with mucopolysaccharidosis VI receiving enzyme replacement therapy in Turkey: a case series

Background

The objective of this study was to describe clinical manifestations and events of patients with mucopolysaccharidosis (MPS) VI in Turkey who are treated with galsulfase enzyme replacement therapy (ERT). Clinical data of 14 children with MPS VI who were followed up at the Department of Pediatrics of the Gazi University Faculty of Medicine in Ankara, Turkey were retrospectively collected from the patients’ medical records. Patients were selected based on availability of a pre-ERT baseline and follow-up clinical data for a similar period of time (1.9–3.2 years). Event data (occurrence of acute clinical events, onset of chronic events, surgeries) collected during hospital visits and telemedicine were available for up to 10 years after initiation of ERT (2.5–10 years).

Results

Age at initiation of ERT ranged from 2.8 to 15.8 years (mean age 7.5 years). All patients presented with reduced endurance and skeletal abnormalities (dysostosis multiplex) on radiography. Other common clinical manifestations were cardiac valve disease (N = 13), short stature (N = 11), cranial abnormalities on MRI (N = 10), spinal abnormalities on MRI (N = 7), and mild cognitive impairment (N = 6). School attendance was generally poor, and several patients had urinary incontinence. After 1.9 to 3.2 years of ERT, most patients showed improvements in endurance in the 6-min walk test and 3-min stair climb tests; the frequency of urinary incontinence decreased. ERT did not seem to prevent progression of cardiac valve disease, eye disorders, hearing loss, or bone disease. Long-term event-based data showed a high incidence of respiratory tract infections, adenotonsillectomy/adenoidectomy, reduced sleep quality, sleep apnea, and depression before initiation of ERT. The number of events tended to remain stable or decrease in all patients over 2.5–10 years follow-up. However, the nature of the events shifted over time, with a reduction in the frequency of respiratory tract infections and sleep problems and an increase in ophthalmologic events, ear tube insertions, and depression.

Conclusions

This case series shows the high disease burden of the MPS VI population in Turkey and provides a unique insight into their clinical journey based on real-life clinical and event-based data collected before and after initiation of ERT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02060-4.

Enzyme replacement therapy with galsulfase for mucopolysaccharidosis type VI

BACKGROUND

Mucopolysaccharidosis type VI (MPS VI) or Maroteaux-Lamy syndrome is a rare genetic disorder caused by the deficiency of arylsulphatase B. The resultant accumulation of dermatan sulphate causes lysosomal damage. The clinical symptoms are related to skeletal dysplasia (i.e. short stature and degenerative joint disease). Other manifestations include cardiac disease, impaired pulmonary function, ophthalmological complications, hepatosplenomegaly, sinusitis, otitis, hearing loss and sleep apnea. Intellectual impairment is generally absent. Clinical manifestation is typically by two or three years of age; however, slowly progressive cases may not present until adulthood. Enzyme replacement therapy (ERT) with galsulfase is considered a new approach for treating MPS VI.

OBJECTIVES

To evaluate the effectiveness and safety of treating MPS VI by ERT with galsulfase compared to other interventions, placebo or no intervention.

SEARCH METHODS

Eletronic searches were performed on the Cystic Fibrosis and Genetic Disorders Group's Inborn Errors of Metabolism Trials Register. Date of the latest search:  09 June 2021. Further searches of the following databases were also performed: CENTRAL, MEDLINE, LILACS, the Journal of Inherited Metabolic Disease, the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov. Date of the latest search: 20 August 2021.

SELECTION CRITERIA

Randomized and quasi-randomized controlled clinical studies of ERT with galsulfase compared to other interventions or placebo.

DATA COLLECTION AND ANALYSIS

Two authors independently screened the studies, assessed the risk of bias, extracted data and assessed the certainty of the the evidence using the GRADE criteria.

MAIN RESULTS

One study was included involving 39 participants who received either ERT with galsulfase (recombinant human arylsulphatase B) or placebo. This small study was considered overall to have an unclear risk of bias in relation to the design and implementation of the study, since the authors did not report how both the allocation generation and concealment were performed. Given the very low certainty of the evidence, we are uncertain whether at 24 weeks there was a difference between groups in relation to the 12-minute walk test, mean difference (MD) of 92.00 meters (95% confidence interval (CI) 11.00 to 172.00), or the three-minute stair climb, MD 5.70 (95% CI -0.10 to 11.50). In relation to respiratory tests, we are uncertain whether galsulfase makes any difference as compared to placebo in forced vital capacity in litres (FVC (L) (absolute change in baseline), given the very low certainty of the evidence. Cardiac function was not reported in the included study. We found that galsulfase, as compared to placebo, may decrease urinary glycosaminoglycan levels at 24 weeks, MD -227.00 (95% CI -264.00 to -190.00) (low-certainty evidence). We are uncertain whether there are differences between the galsulfase and placebo groups in relation to adverse events (very low-certainty evidence). In general, the dose of galsulfase was well tolerated and there were no differences between groups. These events include drug-related adverse events, serious and severe adverse events, those during infusion, drug-related adverse events during infusion, and deaths. More infusion-related reactions were observed in the galsulfase group and were managed with interruption or slowing of infusion rate or administration of antihistamines or corticosteroids drugs. No deaths occurred during the study.   AUTHORS' CONCLUSIONS: The results of this review are based only on one small study (a 24-week randomised phase of the study and prior to the open-label extension). We are uncertain whether galsulfase is more effective than placebo, for treating people with MPS VI, in relation to the 12-minute walk test or the three-minute stair climb, as the certainty of the evidence has been assessed as very low. We found that galsulfase may reduce urinary glycosaminoglycans levels. We are also uncertain whether there are any differences between treatment groups in relation to cardiac or pulmonary functions, liver or spleen volume, overnight apnea-hypopnea, height and weight, quality of life and adverse effects. Further studies are needed to obtain more information on the long-term effectiveness and safety of ERT with galsulfase.

Long-term outcomes of patients with mucopolysaccharidosis VI treated with galsulfase enzyme replacement therapy since infancy

OBJECTIVE

Long-term outcomes of patients with mucopolysaccharidosis (MPS) VI treated with galsulfase enzyme replacement therapy (ERT) since infancy were evaluated.

METHODS

The study was a multicenter, prospective evaluation using data from infants with MPS VI generated during a phase 4 study (ASB-008; Clinicaltrials.govNCT00299000) and clinical data collected ≥5 years after completion of the study.

RESULTS

Parents of three subjects from ASB-008 (subjects 1, 2, and 4) provided written informed consent to participate in the follow-up study. One subject was excluded as consent was not provided. Subjects 1, 2, and 4 were aged 0.7, 0.3, and 1.1 years, respectively, at initiation of galsulfase and 10.5, 7.9, and 10.5 years, respectively, at follow-up. All subjects had classical MPS VI based on pre-treatment urinary glycosaminoglycans and the early onset of clinical manifestations. At follow-up, subject 4 had normal stature for age; subjects 1 and 2 had short stature, but height remained around the 90th percentile of growth curves for untreated classical MPS VI. Six-minute walk distance was normal for age/height in subjects 1 (550 m) and 4 (506 m), and reduced for subject 2 (340 m). Subject 2 preserved normal respiratory function, while percent predicted forced vital capacity and forced expiratory volume in 1 s decreased over time in the other subjects. Skeletal dysplasia was already apparent in all subjects at baseline and continued to progress. Cardiac valve disease showed mild progression in subject 1, mild improvement in subject 4, and remained trivial in subject 2. All subjects had considerably reduced pinch and grip strength at follow-up, but functional dexterity was relatively normal for age and there was limited impact on activities of daily living. Bruininks-Oseretsky Test of Motor Proficiency (BOT-2) results showed that subjects 2 and 4 had numerous fine and gross motor competencies. Corneal clouding progressed in all subjects, while progression of hearing impairment was variable. Liver size normalized from baseline in subjects 1 and 4, and remained normal in subject 2.

CONCLUSION

Very early and continuous ERT appears to slow down the clinical course of MPS VI, as shown by preservation of endurance, functional dexterity, and several fine and gross motor competencies after 7.7-9.8 years of treatment, and less growth impairment or progression of cardiac disease than could be expected based on the patients' classical phenotype. ERT does not seem to prevent progression of skeletal or eye disease in the long term.

The natural history of neurocognition in MPS disorders: A review

MPS disorders are associated with a wide spectrum of neurocognitive effects, from mild problems with attention and executive functions to progressive and degenerative neuronopathic disease. Studies of the natural history of neurocognition are necessary to determine the profile of abnormality and the rates of change, which are crucial to select endpoints for clinical trials of brain treatments and to make clinical recommendations for interventions to improve patients' quality of life. The goal of this paper is to review neurocognitive natural history studies to determine the current state of knowledge and assist in directing future research in all MPS disorders. There are seven different types of MPS diseases, each resulting from a specific enzyme deficiency and each having a separate natural history. MPS IX, will not be discussed as there are only 4 cases reported in the literature without cognitive abnormality. For MPS IH, hematopoietic cell transplant (HCT) is standard of care and many studies have documented the relationship between age at treatment and neurocognitive outcome, and to a lesser extent, neurocognitive status at baseline. However, the mortality and morbidity associated with the transplant process and residual long-term problems after transplant, have led to renewed efforts to find better treatments. Rather than natural history, new trials will likely need to use the developmental trajectories of the patients with HCT as a comparators. The literature has extensive data regarding developmental trajectories post-HCT. For attenuated MPS I, significant neurocognitive deficits have been documented, but more longitudinal data are needed in order to support a treatment directed at their attention and executive function abnormalities. The neuronopathic form of MPS II has been a challenge due to the variability of the trajectory of the disease with differences in timing of slowing of development and decline. Finding predictors of the course of the disease has only been partially successful, using mutation type and family history. Because of lack of systematic data and clinical trials that precede a thorough understanding of the disease, there is need for a major effort to gather natural history data on the entire spectrum of MPS II. Even in the attenuated disease, attention and executive function abnormalities need documentation. Lengthy detailed longitudinal studies are needed to encompass the wide variability in MPS II. In MPS IIIA, the existence of three good natural history studies allowed a quasi-meta-analysis. In patients with a rapid form of the disease, neurocognitive development slowed up until 42 to 47 months, halted up to about 54 months, then declined rapidly thereafter, with a leveling off at an extremely low age equivalent score below 22 months starting at about chronological age of 6. Those with slower or attenuated forms have been more variable and difficult to characterize. Because of the plethora of studies in IIIA, it has been recommended that data be combined from natural history studies to minimize the burden on parents and patients. Sufficient data exists to understand the natural history of cognition in MPS IIIA. MPS IIIB is quite similar to IIIA, but more attenuated patients in that phenotype have been reported. MPS IIIC and D, because they are so rare, have little documentation of natural history despite the prospects of treatments. MPS IV and VI are the least well documented of the MPS disorders with respect to their neurocognitive natural history. Because, like attenuated MPS I and II, they do not show progression of neurocognitive abnormality and most patients function in the range of normality, their behavioral, attentional, and executive function abnormalities have been ignored to the detriment of their quality of life. A peripheral treatment for MPS VII, extremely rare even among MPS types, has recently been approved with a post-approval monitoring system to provide neurocognitive natural history data in the future. More natural history studies in the MPS forms with milder cognitive deficits (MPS I, II, IV, and VI) are recommended with the goal of improving these patients' quality of life with and without new brain treatments, beyond the benefits of available peripheral enzyme replacement therapy. Recommendations are offered at-a-glance with respect to what areas most urgently need attention to clarify neurocognitive function in all MPS types.

The multi-domain responder index: a novel analysis tool to capture a broader assessment of clinical benefit in heterogeneous complex rare diseases

In traditional clinical trial design, efficacy is typically assessed using a single primary endpoint in a randomized controlled trial to detect an expected treatment effect of a therapy in a narrowly selected patient population. This accepted paradigm is based on clinical evaluations that may not actually capture the breadth of the impact of a disease, which is especially true in the setting of complex, multisystem, rare diseases with small, extremely heterogeneous patient populations. The multi-domain responder index (MDRI) is a novel approach that accommodates complex and heterogeneous disease manifestations and evaluates a broad array of clinical disease without impairing the power or rigor of a study to fully understand a treatment. The MDRI sums the scores corresponding to clinically significant thresholds of change for each component domain in each individual patient, capturing the mean clinically meaningful change across multiple domains within individuals. This novel approach combines and then sums the results of independent domain endpoint responder analyses into one responder score to provide a broad basis for the assessment of efficacy. The impact of a treatment across multiple, physiologically independent domains, can be assessed clinically, reducing the adverse impact of heterogeneity on trial outcomes and allowing eligibility criteria to enroll a wider range of patients, ultimately resulting in efficacy and safety assessments of a therapy across a broad group of heterogeneous patients in rare disease programs.

Trial registration The following studies are referenced within this manuscript (CLINICALTRIALS.GOV registration numbers): NCT00912925; NCT00146770; NCT00067470; NCT00104234; NCT00069641; NCT02230566; NCT02377921; NCT02432144.

Novel therapies for mucopolysaccharidosis type III

Mucopolysaccharidosis type III (MPS III) or Sanfilippo disease is an orphan inherited lysosomal storage disease and one of the most common MPS subtypes. The classical presentation is an infantile-onset neurodegenerative disease characterised by intellectual regression, behavioural and sleep disturbances, loss of ambulation, and early death. Unlike other MPS, no disease-modifying therapy has yet been approved. Here, we review the numerous approaches of curative therapy developed for MPS III from historical ineffective haematopoietic stem cell transplantation and substrate reduction therapy to the promising ongoing clinical trials based on enzyme replacement therapy or adeno-associated or lentiviral vectors mediated gene therapy. Preclinical studies are presented alongside the most recent translational first-in-man trials. In addition, we present experimental research with preclinical mRNA and gene editing strategies. Lessons from animal studies and clinical trials have highlighted the importance of an early therapy before extensive neuronal loss. A disease-modifying therapy for MPS III will undoubtedly mandate development of new strategies for early diagnosis.

Hypertrophic Cardiomyopathy in Children: Pathophysiology, Diagnosis, and Treatment of Non-sarcomeric Causes

Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by left ventricular hypertrophy not solely explained by abnormal loading conditions. Despite its rare prevalence in pediatric age, HCM carries a relevant risk of mortality and morbidity in both infants and children. Pediatric HCM is a large heterogeneous group of disorders. Other than mutations in sarcomeric genes, which represent the most important cause of HCM in adults, childhood HCM includes a high prevalence of non-sarcomeric causes, including inherited errors of metabolism (i.e., glycogen storage diseases, lysosomal storage diseases, and fatty acid oxidation disorders), malformation syndromes, neuromuscular diseases, and mitochondrial disease, which globally represent up to 35% of children with HCM. The age of presentation and the underlying etiology significantly impact the prognosis of children with HCM. Moreover, in recent years, different targeted approaches for non-sarcomeric etiologies of HCM have emerged. Therefore, the etiological diagnosis is a fundamental step in designing specific management and therapy in these subjects. The present review aims to provide an overview of the non-sarcomeric causes of HCM in children, focusing on the pathophysiology, clinical features, diagnosis, and treatment of these rare disorders.

Therapy development for the mucopolysaccharidoses: Updated consensus recommendations for neuropsychological endpoints

Neurological dysfunction represents a significant clinical component of many of the mucopolysaccharidoses (also known as MPS disorders). The accurate and consistent assessment of neuropsychological function is essential to gain a greater understanding of the precise natural history of these conditions and to design effective clinical trials to evaluate the impact of therapies on the brain. In 2017, an International MPS Consensus Panel published recommendations for best practice in the design and conduct of clinical studies investigating the effects of therapies on cognitive function and adaptive behavior in patients with neuronopathic mucopolysaccharidoses. Based on an International MPS Consensus Conference held in February 2020, this article provides updated consensus recommendations and expands the objectives to include approaches for assessing behavioral and social-emotional state, caregiver burden and quality of life in patients with all mucopolysaccharidoses.

Mendonça L, Matos L, Prata MJ, S. Jurado A, Pedroso de Lima MC, Alves S. Lysosomal Storage Disease-Associated Neuropathy: Targeting Stable Nucleic Acid Lipid Particle (SNALP)-Formulated siRNAs to the Brain as a Therapeutic Approach

More than two thirds of Lysosomal Storage Diseases (LSDs) present central nervous system involvement. Nevertheless, only one of the currently approved therapies has an impact on neuropathology. Therefore, alternative approaches are under development, either addressing the underlying enzymatic defect or its downstream consequences. Also under study is the possibility to block substrate accumulation upstream, by promoting a decrease of its synthesis. This concept is known as substrate reduction therapy and may be triggered by several molecules, such as small interfering RNAs (siRNAs). siRNAs promote RNA interference, a naturally occurring sequence-specific post-transcriptional gene-silencing mechanism, and may target virtually any gene of interest, inhibiting its expression. Still, naked siRNAs have limited cellular uptake, low biological stability, and unfavorable pharmacokinetics. Thus, their translation into clinics requires proper delivery methods. One promising platform is a special class of liposomes called stable nucleic acid lipid particles (SNALPs), which are characterized by high cargo encapsulation efficiency and may be engineered to promote targeted delivery to specific receptors. Here, we review the concept of SNALPs, presenting a series of examples on their efficacy as siRNA nanodelivery systems. By doing so, we hope to unveil the therapeutic potential of these nanosystems for targeted brain delivery of siRNAs in LSDs.

Retrospective chart review of urinary glycosaminoglycan excretion and long-term clinical outcomes of enzyme replacement therapy in patients with mucopolysaccharidoses

BACKGROUND

Mucopolysaccharidoses (MPS) are a group of rare, inherited metabolic diseases that result from a deficiency in one of several lysosomal enzymes essential for stepwise glycosaminoglycan (GAG) degradation, leading to GAG accumulation and widespread cellular pathology and clinical disease. Although disease presentation is heterogeneous, the clinical hallmarks are largely comparable across several MPS subtypes. Extensive data have shown that the level of urinary GAG (uGAG) excretion above normal is strongly correlated with disease severity and clinical outcomes in MPS diseases. Thus, change in uGAG excretion may have significant value as a potential primary endpoint in clinical trials of MPS diseases that are too rare to study using traditional clinical endpoints.

METHODS

A retrospective medical chart review was undertaken of patients with MPS I, II, and VI who had been treated long term with enzyme replacement therapy (ERT). The relationship between uGAG reduction and clinical outcomes relevant to the major clinical manifestations of these MPS diseases was evaluated. A multi-domain responder index (MDRI) score was calculated, measuring the following 4 domains: 6-min walk test, pulmonary function, growth rate, and Clinician Global Impression of Change. For each domain, a minimal important difference (MID) was defined based on published information of these outcome measures in MPS and other diseases.

RESULTS

Of the 50 patients evaluated, 18 (36%) had MPS I, 23 (46%) had MPS II, and 9 (18%) had MPS VI. Forty-two were clinical practice patients and 8 had participated in clinical trials. Across all MPS subtypes, the mean (± SD) uGAG level at baseline was 66.0 ± 51.5 mg/mmol creatinine (n = 48) and there was a mean reduction of 54.6% following ERT. Analysis of the MDRI score based on the MID defined for each domain showed a greater magnitude of improvement in patients with increased uGAG reduction when compared with those patients with lower uGAG reduction for all assessed uGAG thresholds, and a trend toward a higher likelihood of positive mean MDRI score in patients with a uGAG reduction ≥40%.

CONCLUSIONS

In this retrospective study, uGAG reduction was associated with long-term clinical outcomes as assessed by a number of approaches, supporting the use of uGAG reduction as a biomarker primary endpoint.

Pharmacokinetic and Pharmacodynamic Modeling to Optimize the Dose of Vestronidase Alfa, an Enzyme Replacement Therapy for Treatment of Patients with Mucopolysaccharidosis Type VII: Results from Three Trials

Introduction

Mucopolysaccharidosis type VII (MPS VII, Sly Syndrome) is a progressive, debilitating, ultra-rare lysosomal storage disorder caused by the deficiency of β-glucuronidase (GUS), an enzyme required for breakdown of glycosaminoglycans (GAGs). Vestronidase alfa, a recombinant human GUS, is an enzyme replacement therapy approved in the US and EU for the treatment of MPS VII.

Methods

The pharmacokinetics (PK) and pharmacodynamics (PD) of vestronidase alfa were evaluated in 23 adult and pediatric subjects with MPS VII enrolled in phase I–III clinical trials to optimize the clinical dosing regimen of vestronidase alfa. The serum concentration-time profiles were adequately described by a two-compartment population PK model incorporating subjects’ body weight as the only significant covariate.

Results

Model-based simulations predicted a substantially decreased time duration of serum exposures exceeding the level of K_uptake (the in vitro determined vestronidase alfa concentration corresponding to 50% maximum rate of cellular uptake) for 4 or 8 mg/kg once every 4 weeks dosing, compared with 4 mg/kg once every other week (QOW) dosing by intravenous infusion, suggesting that given the same total monthly dose, the QOW dosing frequency should result in more efficient delivery to the GUS-deficient tissue cells, and therefore superior treatment efficacy. A standard inhibitory maximal effect model reasonably explained the observed pharmacological PD responses of reduction in urinary GAGs from pretreatment baseline, which appeared to have reached the plateau of maximal effect at the 4 mg/kg QOW dose.

Conclusion

The modeling results, together with the clinical evidence of safety and efficacy, supported the recommended 4 mg/kg QOW dosing regimen of vestronidase alfa for pediatric and adult patients with MPS VII.

Clinical Trial Registration

NCT01856218, NCT02418455, NCT02230566.

Electronic supplementary material

The online version of this article (10.1007/s40262-018-0721-y) contains supplementary material, which is available to authorized users.

Urinary glycosaminoglycans as a potential biomarker for evaluating treatment efficacy in subjects with mucopolysaccharidoses

Accumulations of glycosaminoglycans (GAGs) that result from deficiencies in lysosomal hydrolases are characteristic of mucopolysaccharidoses (MPS). Enzyme replacement therapies (ERTs) are now available for several MPS diseases (MPS I, MPS II, MPS IVA, MPS VI, and MPS VII), but assessment of the efficacy of treatment can be challenging because these are rare, progressive, and highly heterogeneous diseases; because some clinical manifestations may be irreversible if treatment initiation is delayed; and because determining the benefits of a treatment to prevent those manifestations may take prolonged periods of time. In addition to accumulation of GAGs in tissues, elevated urinary GAG (uGAG) levels are evident and are reduced rapidly after initiation of ERT. Studies in MPS animal models and clinical studies in subjects with MPS diseases have revealed correlations between reductions of uGAG levels and clinical effects of ERTs. In this article, we review the growing body of evidence to support the potential for the use of uGAG levels as predictive biomarkers of treatment efficacy.

Intravenous Enzyme Replacement Therapy in Mucopolysaccharidoses: Clinical Effectiveness and Limitations

The aim of this review is to summarize the evidence on efficacy, effectiveness and safety of intravenous enzyme replacement therapy (ERT) available for mucopolysaccharidoses (MPSs) I, II, IVA, VI and VII, gained in phase III clinical trials and in observational post-approval studies. Post-marketing data are sometimes conflicting or controversial, possibly depending on disease severity, differently involved organs, age at starting treatment, and development of anti-drug antibodies (ADAs). There is general agreement that ERT is effective in reducing urinary glycosaminoglycans and liver and spleen volume, while heart and joints outcomes are variable in different studies. Effectiveness on cardiac valves, trachea and bronchi, hearing and eyes is definitely poor, probably due to limited penetration in the specific tissues. ERT does not cross the blood–brain barrier, with the consequence that the central nervous system is not cured by intravenously injected ERT. All patients develop ADAs but their role in ERT tolerance and effectiveness has not been well defined yet. Lack of reliable biomarkers contributes to the uncertainties about effectiveness. The data obtained from affected siblings strongly indicates the need of neonatal screening for treatable MPSs. Currently, other treatments are under evaluation and will surely help improve the prognosis of MPS patients.

Diagnosis of Mucopolysaccharidoses

The mucopolysaccharidoses (MPSs) include 11 different conditions caused by specific enzyme deficiencies in the degradation pathway of glycosaminoglycans (GAGs). Although most MPS types present increased levels of GAGs in tissues, including blood and urine, diagnosis is challenging as specific enzyme assays are needed for the correct diagnosis. Enzyme assays are usually performed in blood, with some samples (as leukocytes) providing a final diagnosis, while others (such as dried blood spots) still being considered as screening methods. The identification of variants in the specific genes that encode each MPS-related enzyme is helpful for diagnosis confirmation (when needed), carrier detection, genetic counseling, prenatal diagnosis (preferably in combination with enzyme assays) and phenotype prediction. Although the usual diagnostic flow in high-risk patients starts with the measurement of urinary GAGs, it continues with specific enzyme assays and is completed with mutation identification; there is a growing trend to have genotype-based investigations performed at the beginning of the investigation. In such cases, confirmation of pathogenicity of the variants identified should be confirmed by measurement of enzyme activity and/or identification and/or quantification of GAG species. As there is a growing number of countries performing newborn screening for MPS diseases, the investigation of a low enzyme activity by the measurement of GAG species concentration and identification of gene mutations in the same DBS sample is recommended before the suspicion of MPS is taken to the family. With specific therapies already available for most MPS patients, and with clinical trials in progress for many conditions, the specific diagnosis of MPS as early as possible is becoming increasingly necessary. In this review, we describe traditional and the most up to date diagnostic methods for mucopolysaccharidoses.

The long-term safety and efficacy of vestronidase alfa, rhGUS enzyme replacement therapy, in subjects with mucopolysaccharidosis VII

Vestronidase alfa (recombinant human beta-glucuronidase) is an enzyme replacement therapy (ERT) for Mucopolysaccharidosis (MPS) VII, a highly heterogeneous, ultra-rare disease. Twelve subjects, ages 8-25 years, completed a Phase 3, randomized, placebo-controlled, blind-start, single crossover study (UX003-CL301; NCT02377921), receiving 24-48 weeks of vestronidase alfa 4 mg/kg IV. All 12 subjects completed the blind-start study, which showed significantly reduced urinary glycosaminoglycans (GAG) and clinical improvement in a multi-domain responder index, and enrolled in a long-term, open-label, extension study (UX003-CL202; NCT02432144). Here, we report the final results of the extension study, up to an additional 144 weeks after completion of the blind-start study. Three subjects (25%) completed all 144 weeks of study, eight subjects (67%) ended study participation before Week 144 to switch to commercially available vestronidase alfa, and one subject discontinued due to non-compliance after receiving one infusion of vestronidase alfa in the extension study. The safety profile of vestronidase alfa in the extension study was consistent with observations in the preceding blind-start study, with most adverse events mild to moderate in severity. There were no treatment or study discontinuations due to AEs and no noteworthy changes in a standard safety chemistry panel. Out of the eleven subjects who tested positive for anti-drug antibodies at any time during the blind-start or extension study, including the baseline assessment in the blind-start study, seven subjects tested positive for neutralizing antibodies and all seven continued to demonstrate a reduction in urinary GAG levels. There was no association between antibody formation and infusion associated reactions. Subjects receiving continuous vestronidase alfa treatment showed a sustained urinary GAG reduction and clinical response evaluated using a multi-domain responder index that includes assessments in pulmonary function, motor function, range of motion, mobility, and visual acuity. Reduction in fatigue was also maintained in the overall population. As ERT is not expected to cross the blood brain barrier, limiting the impact on neurological signs of disease, and not all subjects presented with neurological symptoms, outcomes related to central nervous system pathology are not focused on in this report. Results from this study show the long-term safety and durability of clinical efficacy in subjects with MPS VII with long-term vestronidase alfa treatment.

A Cure for Sanfilippo Syndrome? A Summary of Current Therapeutic Approaches and their Promise

Mucopolysaccharidoses III (MPS III, Sanfilippo syndrome) is a subtype of the Mucopolysaccharidoses (MPS), a group of inherited lysosomal disorders caused by a deficiency of lysosomal enzymes responsible for catabolizing glycosaminoglycans (GAGs). Although MPS III is rare, MPS diseases as a group are relatively frequent with an overall incidence of approximately 1 in 20,000 - 25,000 births. MPS III are paediatric diseases, which cause learning difficulties, behavioural disorders and dementia, as well as skeletal deformities and ultimately result in premature death. There are currently no approved treatments for MPS III, but a number of therapeutic approaches are under development. In the past 30 years, research using cellular and animal models have led to clinical trials involving enzyme replacement therapy (ERT), substrate reduction therapy (SRT) and gene therapy, while stem cells approaches remain at the pre-clinical stage. Although safety and clinical efficacy in animal models have shown promise, the results of clinical trials have proved costly and shown limited therapeutic effects. In this review, we describe the most recent results from clinical trials. While ERT and gene therapy are the most developed therapies for MPS III, we highlight the work that needs to be done to bring us closer to a real treatment for these devastating diseases.

C-Type Natriuretic Peptide Restores Growth Impairment Under Enzyme Replacement in Mice With Mucopolysaccharidosis VII

Growth impairment in mucopolysaccharidoses (MPSs) is an unresolved issue as it is resistant to enzyme replacement therapy (ERT) and growth hormone therapy. C-type natriuretic peptide (CNP) is a promising agent that has growth-promoting effects. Here we investigate the effects of CNP on growth impairment of MPSs using Gusbmps-2J mice, a model for MPS type VII, with combination therapy of CNP and ERT by hydrodynamic gene delivery. Although monotherapies were not sufficient to restore short statures of treated mice, combination therapy resulted in successful restoration. The synergistic effects of CNP and ERT were not only observed in skeletal growth but also in growth plates. ERT reduced cell swelling in the resting zone and increased cell number by accelerating proliferation or inhibiting apoptosis. CNP thickened the proliferative and hypertrophic zones. Regarding changes in the bone, ERT restored bone sclerosis through decreased bone formation and increased bone resorption, and CNP did not adversely affect this process. In addition, improvement of joint deformation by ERT was suggested by analyses of joint spaces and articular cartilage. CNP additively provided restoration of the short stature of MPS VII mice in combination with ERT, which improved abnormalities of growth plates and bone metabolism.

Targeted delivery of lysosomal enzymes to the endocytic compartment in human cells using engineered extracellular vesicles

Targeted delivery of lysosomal enzymes to the endocytic compartment of human cells represents a transformative technology for treating a large family of lysosomal storage diseases (LSDs). Gaucher disease is one of the most common types of LSDs caused by mutations to the lysosomal β-glucocerebrosidase (GBA). Here, we describe a genetic strategy to produce engineered exosomes loaded with GBA in two different spatial configurations for targeted delivery to the endocytic compartment of recipient cells. By fusing human GBA to an exosome-anchoring protein: vesicular stomatitis virus glycoprotein (VSVG), we demonstrate that the chimeric proteins were successfully integrated into exosomes which were secreted as extracellular vesicles (EVs) by producer cells. Isolation and molecular characterization of EVs confirmed that the fusion proteins were loaded onto exosomes without altering their surface markers, particle size or distribution. Further, enzyme-loaded exosomes/EVs added to cultured medium were taken up by recipient cells. Further, the endocytosed exosomes/EVs targeted to endocytic compartments exhibited a significant increase in GBA activity. Together, we have developed a novel method for targeting and delivery of lysosomal enzymes to their natural location: the endocytic compartment of recipient cells. Since exosomes/EVs have an intrinsic ability to cross the blood-brain-barrier, our technology may provide a new approach to treat severe types of LSDs, including Gaucher disease with neurological complications.

Enzyme replacement therapy for mucopolysaccharidoses; past, present, and future

Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorders, which lack an enzyme corresponding to the specific type of MPS. Enzyme replacement therapy (ERT) has been the standard therapeutic option for some types of MPS because of the ability to start immediate treatment with feasibility and safety and to improve prognosis. There are several disadvantages for current ERT, such as limited impact to the brain and avascular cartilage, weekly or biweekly infusions lasting 4-5 h, the immune response against the infused enzyme, a short half-life, and the high cost. Clinical studies of ERT have shown limited efficacy in preventing or resolving progression in neurological, cardiovascular, and skeletal diseases. One focus is to penetrate the avascular cartilage area to at least stabilize, if not reverse, musculoskeletal diseases. Although early intervention in some types of MPS has shown improvements in the severity of skeletal dysplasia and stunted growth, this limits the desired effect of ameliorating musculoskeletal disease progression to young MPS patients. Novel ERT strategies are under development to reach the brain: (1) utilizing a fusion protein with monoclonal antibody to target a receptor on the BBB, (2) using a protein complex from plant lectin, glycan, or insulin-like growth factor 2, and (3) direct infusion across the BBB. As for MPS IVA and VI, bone-targeting ERT will be an alternative to improve therapeutic efficacy in bone and cartilage. This review summarizes the effect and limitations on current ERT for MPS and describes the new technology to overcome the obstacles of conventional ERT.

Therapeutic Options for Mucopolysaccharidoses: Current and Emerging Treatments

Mucopolysaccharidoses (MPS) are inborn errors of metabolism produced by a deficiency of one of the enzymes involved in the degradation of glycosaminoglycans (GAGs). Although taken separately, each type is rare. As a group, MPS are relatively frequent, with an overall estimated incidence of around 1 in 20,000-25,000 births. Development of therapeutic options for MPS, including hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT), has modified the natural history of many MPS types. In spite of the improvement in some tissues and organs, significant challenges remain unsolved, including blood-brain barrier (BBB) penetration and treatment of lesions in avascular cartilage, heart valves, and corneas. Newer approaches, such as intrathecal ERT, ERT with fusion proteins to cross the BBB, gene therapy, substrate reduction therapy (SRT), chaperone therapy, and some combination of these strategies may provide better outcomes for MPS patients in the near future. As early diagnosis and early treatment are imperative to improve therapeutic efficacy, the inclusion of MPS in newborn screening programs should enhance the potential impact of treatment in reducing the morbidity associated with MPS diseases. In this review, we evaluate available treatments, including ERT and HSCT, and future treatments, such as gene therapy, SRT, and chaperone therapy, and describe the advantages and disadvantages. We also assess the current clinical endpoints and biomarkers used in clinical trials.

Individual heat map assessments demonstrate vestronidase alfa treatment response in a highly heterogeneous mucopolysaccharidosis VII study population

Mucopolysaccharidosis (MPS) VII is an ultra-rare, progressively debilitating, life-threatening lysosomal disease caused by deficiency of the enzyme, β-glucuronidase. Vestronidase alfa is an approved enzyme replacement therapy for MPS VII. UX003-CL301 was a phase 3, randomized, placebo-controlled, blind-start study examining the efficacy and safety of vestronidase alfa 4 mg/kg intravenously administered every 2 weeks to 12 patients with MPS VII. Due to the rarity of disease, broad eligibility criteria resulted in a highly heterogeneous population with variable symptoms. For an integrated view of the diverse data, the changes from baseline (or randomization for the placebo period) in clinical endpoints were grouped into three functional domains (mobility, fatigue, and fine motor + self-care) and analyzed post-hoc as subject-level heat maps. Mobility assessments included the 6-minute walk test, 3-minute stair climb test, Bruininks-Oseretsky test (BOT-2) gross motor function subtests, and patient-reported outcome assessments (PROs) related to movement, pain, and ambulation. Fatigue assessments included the Pediatric Quality of Life Multidimensional Fatigue Scale and other fatigue-related PROs. Fine motor + self-care assessments included BOT-2 fine motor function subtests and PROs for eating, dressing, hygiene, and caregiver assistance. Most subjects showed improvement in at least one domain. Two subjects improved in two or more domains and two subjects did not show clear improvement in any domain. Both severely and mildly affected subjects improved with vestronidase alfa in clinical assessments, PRO results, or both. Heat map analysis demonstrates how subjects responded to treatment across multiple domains, providing a useful visual tool for studying rare diseases with variable symptoms.

Vestronidase Alfa: A Review in Mucopolysaccharidosis VII

Mucopolysaccharidosis VII is an extremely rare, autosomal recessive lysosomal storage disorder characterized by a deficiency of β-glucuronidase activity, resulting in partial degradation and accumulation of GAGs in numerous tissues throughout the body, with consequent cellular damage and organ dysfunction. Enzyme replacement therapy (ERT) with intravenous vestronidase alfa (Mepsevii™), a recombinant form of human β-glucuronidase, is the first disease-specific therapy approved for the treatment of mucopolysaccharidosis VII in pediatric and adult patients. In the pivotal, blind start, phase 3 trial, 24 weeks of vestronidase alfa therapy significantly reduced urinary GAG (uGAG) excretion in patients with mucopolysaccharidosis VII. Based on a Multi-Domain Responder Index (MDRI; comprises six clinically important morbidity domains, with prespecified minimally important differences for each domain), most evaluable patients experienced an improvement in ≥ 1 domain during the 24-week primary assessment period (overall positive mean change of 0.5 domains). The clinical benefits of vestronidase alfa were sustained during longer-term treatment, as was the reduction in uGAG excretion. Vestronidase alfa has a manageable tolerability profile, with most adverse reactions of mild to moderate severity. Given the lack of treatment options and the clinical benefits it provides, intravenous vestronidase alfa is an important emerging ERT for patients with mucopolysaccharidosis VII.

Enzyme replacement therapy initiated in adulthood: Findings from the mucopolysaccharidosis VI Clinical Surveillance Program

OBJECTIVE

To evaluate the impact of galsulfase enzyme replacement therapy (ERT) when initiated in adulthood for patients with mucopolysaccharidosis (MPS) VI.

METHODS

In 2005, the multi-national, MPS VI Clinical Surveillance Program (CSP) was established to collect long-term observational data from routine clinical and laboratory assessments. A sub-analysis was performed in patients who started ERT at ≥16 years of age and had received galsulfase for ≥6 months. Urinary glycosaminoglycans (uGAG), 6-min walk test (6MWT), 3-min stair climb test (3MSCT), pulmonary function measures, cardiac function, ophthalmology measures, liver and spleen sizes, and safety were evaluated.

RESULTS

Of 223 patients enrolled in the CSP, 51 were included in the sub-analysis. Patients were between 16 and 63 years of age at first infusion. From pre-treatment baseline, uGAG level decreased by a mean (±standard deviation [SD]) of 66 (±45)% (N = 29) after a median follow-up of 7.2 years. 6MWT distance decreased slightly by a mean of 17 (±107) meters (N = 23) after 6.6 years. Stairs/min in the 3MSCT increased by a mean of 26 (±33) (N = 14) after 2.8 years. Pulmonary function measures, forced expiratory volume in 1 second and forced vital capacity, increased by a mean of 0.06 (±0.21) L after 7.3 years and 0.05 (±0.28) L after 7.2 years, respectively (N = 19 for both measures). Overall, galsulfase was well tolerated, with most adverse events reported being MPS-related clinical manifestations and not related to galsulfase.

CONCLUSIONS

Results of this sub-analysis of the CSP suggest that initiation of galsulfase in adulthood is well tolerated and can possibly stabilize MPS VI in the long term.

Recommendations for the management of MPS VI: systematic evidence- and consensus-based guidance

Introduction

Mucopolysaccharidosis (MPS) VI or Maroteaux-Lamy syndrome (253200) is an autosomal recessive lysosomal storage disorder caused by deficiency in N-acetylgalactosamine-4-sulfatase (arylsulfatase B). The heterogeneity and progressive nature of MPS VI necessitates a multidisciplinary team approach and there is a need for robust guidance to achieve optimal management. This programme was convened to develop evidence-based, expert-agreed recommendations for the general principles of management, routine monitoring requirements and the use of medical and surgical interventions in patients with MPS VI.

Methods

26 international healthcare professionals from various disciplines, all with expertise in managing MPS VI, and three patient advocates formed the Steering Committee group (SC) and contributed to the development of this guidance. Members from six Patient Advocacy Groups (PAGs) acted as advisors and attended interviews to ensure representation of the patient perspective. A modified-Delphi methodology was used to demonstrate consensus among a wider group of healthcare professionals with expertise and experience managing patients with MPS VI and the manuscript has been evaluated against the validated Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument by three independent reviewers.

Results

A total of 93 guidance statements were developed covering five domains: (1) general management principles; (2) recommended routine monitoring and assessments; (3) enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT); (4) interventions to support respiratory and sleep disorders; (5) anaesthetics and surgical interventions. Consensus was reached on all statements after two rounds of voting. The greatest challenges faced by patients as relayed by consultation with PAGs were deficits in endurance, dexterity, hearing, vision and respiratory function. The overall guideline AGREE II assessment score obtained for the development of the guidance was 5.3/7 (where 1 represents the lowest quality and 7 represents the highest quality of guidance).

Conclusion

This manuscript provides evidence- and consensus-based recommendations for the management of patients with MPS VI and is for use by healthcare professionals that manage the holistic care of patients with the intention to improve clinical- and patient-reported outcomes and enhance patient quality of life. It is recognised that the guidance provided represents a point in time and further research is required to address current knowledge and evidence gaps.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1080-y) contains supplementary material, which is available to authorized users.

Enzyme replacement therapy outcomes across the disease spectrum: Findings from the mucopolysaccharidosis VI Clinical Surveillance Program

The impact of galsulfase enzyme replacement therapy in patients with mucopolysaccharidosis (MPS) VI with phenotypes at either end of the disease spectrum was evaluated. The MPS VI Clinical Surveillance Program (CSP) was established to collect long-term observational data from routine clinical and laboratory assessments. A subanalysis of the CSP was performed in patients with pretreatment urinary glycosaminoglycan (uGAG) levels <100 μg/mg and ≥200 μg/mg creatinine (low- and high-uGAG) who had received galsulfase for ≥6 months. uGAG, 6-minute walk test (6MWT), 3-minute stair climb test (3MSCT), pulmonary function measures, height/growth, cardiac function, and safety were evaluated. Patients with a high-uGAG level at pre-treatment baseline (N = 68) showed greater impairments in endurance and pulmonary function than those with low-baseline uGAG levels (N = 39). From pre-treatment baseline, the distance walked on the 6MWT in the low- and high-uGAG groups increased by a mean (±SD) of 49 (±151) meters and 42 (±165) meters (median follow-up 5.5 and 7.7 years), respectively. The number of stairs/min climbed in the 3MSCT in the low- and high-uGAG groups increased by a mean of 18 (±33) and 30 (±45) (median follow-up 2.8 and 3.5 years), respectively. Overall, pulmonary function remained unchanged for both groups. No impact was seen on cardiac function. Galsulfase was generally well tolerated in both groups, with most adverse events being MPS-related complications unrelated to galsulfase. Results of this CSP sub-analysis suggest that galsulfase stabilizes MPS VI in the long-term and has an acceptable safety profile, regardless of baseline disease severity.

Reliability and Validity of the 6-Minute Walk Test in Hypophosphatasia

This investigation evaluated the reliability and validity of the 6‐Minute Walk Test (6MWT) in patients with pediatric hypophosphatasia (HPP). Children (aged 6 to 12 years; n = 11), adolescents (13 to 17 years; n = 4), and adults (18 to 65 years; n = 9) completed the 6MWT at screening and baseline in two clinical studies of asfotase alfa. Test‐retest reliability of the 6MWT, evaluated with Pearson's correlation coefficients (r) for screening versus baseline, was high for children (r = 0.95; p < 0.0001), adolescents (r = 0.81; p = 0.125), and adults (r = 0.94; p = 0.0001). The most conservative minimal clinically important differences, estimated using distribution‐based methods, were 31 m (children and adults) and 43 m (adolescents). In children, the 6MWT correlated significantly with scores on measures of skeletal disease, which included the Radiographic Global Impression of Change scale (r = 0.50; p < 0.0001) and the Rickets Severity Scale (r = −0.78; p < 0.0001), such that distance walked increased as the severity of skeletal disease decreased. Significant (p < 0.0001) correlations with the 6MWT distance walked were also observed for children with scores on parent‐reported measures of disability (r = −0.67), ability to function in activities of daily living (r = 0.71 to 0.77), and parent‐reported measures of pain (r = −0.39). In adolescents and adults, 6MWT distance walked correlated significantly (p < 0.05) with measures of lower extremity function (r = 0.83 and 0.60, respectively), total pain severity (r = −0.41 and −0.36, respectively), and total pain interference (r = −0.41 and −0.49, respectively). Collectively, these data indicate that the 6MWT is a reliable, valid measure of physical functioning in patients with pediatric HPP. © 2018 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Hematopoietic Stem Cell Transplantation for Mucopolysaccharidoses: Past, Present, and Future

Allogenic hematopoietic stem cell transplantation (HSCT) has proven to be a viable treatment option for a selected group of patients with mucopolysaccharidoses (MPS), including those with MPS types I, II, IVA, VI, and VII. Early diagnosis and timely referral to an expert in MPS are critical, followed by a complete examination and evaluation by a multidisciplinary team, including a transplantation physician. Treatment recommendations for MPS are based on multiple biological, sociological, and financial factors, including type of MPS, clinical severity, prognosis, present clinical signs and symptoms (disease stage), age at onset, rate of progression, family factors and expectations, financial burden, feasibility, availability, risks and benefits of available therapies such as HSCT, enzyme replacement therapy (ERT), surgical interventions, and other supportive care. International collaboration and data review are critical to evaluating the therapeutic efficacy and adverse effects of HSCT for MPS. Collaborative efforts to assess HSCT for MPS have been ongoing since the first attempt at HSCT in a patient with MPS reported in 1981. The accumulation of data since then has made it possible to identify early outcomes (ie, transplantation outcomes) and long-term disease-specific outcomes resulting from HSCT. The recent identification of predictive factors and the development of innovative regimens have significantly improved the outcomes of both engraftment failure and transplantation-related mortality. Assessment of long-term outcomes has considered a variety of factors, including type of MPS, type of graft, age at transplantation, and stage of disease progression, among others. Studies on long-term outcomes are considered a key factor in the use of HSCT in patients with MPS. These studies have shown the effects and limitations of HSCT on improving disease manifestations and quality of life. In this review, we summarize the efficacy, side effects, risks, and cost of HSCT for each type of MPS.

Clinical effectiveness of enzyme replacement therapy with galsulfase in mucopolysaccharidosis type VI treatment: Systematic review

INTRODUCTION

Mucopolysaccharidosis VI is a rare disease characterized by the arylsulfatase B enzyme deficiency, which is responsible for different clinical manifestations. The treatment consists of enzyme replacement therapy with intravenous administration of galsulfase.

OBJECTIVE

Evaluate the effectiveness of the enzyme replacement therapy with galsulfase for the mucopolysaccharidosis VI treatment.

METHOD

Systematic review of observational studies. The databases of PubMed, Cochrane Library, Lilacs, and Journal of Inherited Metabolic Disease were reviewed. The selection of studies, data mining, and methodological quality assessment were independently conducted by two authors.

RESULTS

Eighteen studies fulfilled the inclusion criteria. Two studies were cohorts, one was longitudinal study, one was cross-sectional, one was a case-control, eight were case series, and five were case reports. A total of 362 participants with mucopolysaccharidosis type VI were evaluated, and 14 different outcomes related to the treatment effect were identified. Seven outcomes showed positive results, characterized by the patient survival, quality of life, respiratory function, joint mobility, physical resistance, reduction of urinary glycosaminoglycans, and growth. The hearing function and the cognitive development were stable after the treatment. Other outcomes related to the cardiac function, visual acuity, sleep apnea, and the size of the liver and spleen presented inconclusive outcomes. Concerning safety, light adverse reactions of hypersensitivity were reported.

CONCLUSION

This review provided a broader panoramic view of the outcomes related to mucopolysaccharidosis type VI. Regardless of the inherent limitations of observational studies, the outcomes indicate that the enzyme replacement therapy has a positive effect on most of the outcomes associated to the disease.

Enzyme replacement therapy: efficacy and limitations

Enzyme replacement therapy (ERT) is available for mucopolysaccharidosis (MPS) I, MPS II, MPS VI, and MPS IVA. The efficacy of ERT has been evaluated in clinical trials and in many post-marketing studies with a long-term follow-up for MPS I, MPS II, and MPS VI. While ERT is effective in reducing urinary glycosaminoglycans (GAGs) and liver and spleen volume, cartilaginous organs such as the trachea and bronchi, bones and eyes are poorly impacted by ERT probably due to limited penetration in the specific tissue. ERT in the present formulations also does not cross the blood–brain barrier, with the consequence that the central nervous system is not cured by ERT. This is particularly important for severe forms of MPS I and MPS II characterized by cognitive decline. For severe MPS I patients (Hurler), early haematopoietic stem cell transplantation is the gold standard, while still controversial is the role of stem cell transplantation in MPS II. The use of ERT in patients with severe cognitive decline is the subject of debate; the current position of the scientific community is that ERT must be started in all patients who do not have a more effective treatment. Neonatal screening is widely suggested for treatable MPS, and many pilot studies are ongoing. The rationale is that early, possibly pre-symptomatic treatment can improve prognosis. All patients develop anti-ERT antibodies but only a few have drug-related adverse reactions. It has not yet been definitely clarified if high-titre antibodies may, at least in some cases, reduce the efficacy of ERT.

Genetically Corrected iPSC-Derived Neural Stem Cell Grafts Deliver Enzyme Replacement to Affect CNS Disease in Sanfilippo B Mice

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB [MPS IIIB]) is a lysosomal storage disorder primarily affecting the brain that is caused by a deficiency in the enzyme α-N-acetylglucosaminidase (NAGLU), leading to intralysosomal accumulation of heparan sulfate. There are currently no treatments for this disorder. Here we report that, ex vivo, lentiviral correction of Naglu-/- neural stem cells derived from Naglu-/- mice (iNSCs) corrected their lysosomal pathology and allowed them to secrete a functional NAGLU enzyme that could be taken up by deficient cells. Following long-term transplantation of these corrected iNSCs into Naglu-/- mice, we detected NAGLU activity in the majority of engrafted animals. Successfully transplanted Naglu-/- mice showed a significant decrease in storage material, a reduction in astrocyte activation, and complete prevention of microglial activation within the area of engrafted cells and neighboring regions, with beneficial effects extending partway along the rostrocaudal axis of the brain. Our results demonstrate long-term engraftment of iNSCs in the brain that are capable of cross-correcting pathology in Naglu-/- mice. Our findings suggest that genetically engineered iNSCs could potentially be used to deliver enzymes and treat MPS IIIB.

Mucopolysaccharidosis type VI (MPS VI) and molecular analysis: Review and classification of published variants in the ARSB gene

Maroteaux–Lamy syndrome (MPS VI) is an autosomal recessive lysosomal storage disorder caused by pathogenic ARSB gene variants, commonly diagnosed through clinical findings and deficiency of the arylsulfatase B (ASB) enzyme. Detection of ARSB pathogenic variants can independently confirm diagnosis and render genetic counseling possible. In this review, we collect and summarize 908 alleles (201 distinct variants, including 3 polymorphisms previously considered as disease‐causing variants) from 478 individuals diagnosed with MPS VI, identified from literature and public databases. Each variant is further analyzed for clinical classification according to American College of Medical Genetics and Genomics (ACMG) guidelines. Results highlight the heterogeneity of ARSB alleles, with most unique variants (59.5%) identified as missense and 31.7% of unique alleles appearing once. Only 18% of distinct variants were previously recorded in public databases with supporting evidence and clinical significance. ACMG recommends publishing clinical and biochemical data that accurately characterize pathogenicity of new variants in association with reporting specific alleles. Variants analyzed were sent to ClinVar (https://www.ncbi.nlm.nih.gov/clinvar/), and MPS VI locus‐specific database (http://mps6-database.org) where they will be available. High clinical suspicion coupled with diagnostic testing for deficient ASB activity and timely submission and classification of ARSB variants with biochemical and clinical data in public databases is essential for timely diagnosis of MPS VI.

The relationships between urinary glycosaminoglycan levels and phenotypes of mucopolysaccharidoses

Background

The aim of this study was to use the liquid chromatography/tandem mass spectrometry (LC‐MS/MS) method to quantitate levels of three urinary glycosaminoglycans (GAGs; dermatan sulfate [DS], heparan sulfate [HS], and keratan sulfate [KS]) to help make a correct diagnosis of mucopolysaccharidosis (MPS).

Methods

We analyzed the relationships between phenotypes and levels of urinary GAGs of 79 patients with different types of MPS.

Results

The patients with mental retardation (n = 21) had significantly higher levels of HS than those without mental retardation (n = 58; 328.8 vs. 3.2 μg/ml, p < 0.001). The DS levels in the patients with hernia, hepatosplenomegaly, claw hands, coarse face, valvular heart disease, and joint stiffness were higher than those without. Twenty patients received enzyme replacement therapy (ERT) for 1–12.3 years. After ERT, the KS level decreased by 90% in the patients with MPS IVA compared to a 31% decrease in the change of dimethylmethylene blue (DMB) ratio. The DS level decreased by 79% after ERT in the patients with MPS VI compared to a 66% decrease in the change of DMB ratio.

Conclusions

The measurement of GAG fractionation biomarkers using the LC‐MS/MS method is a more sensitive and reliable tool than the DMB ratio for MPS high‐risk screening, diagnosis, subclass identification, and monitoring the efficacy of ERT.

A novel mutation in the NAGLU gene associated with Sanfilippo syndrome type B (mucopolysaccharidosis III B)

Homozygous or compound heterozygous mutation in the gene encoding N-alpha-acetylglucosaminidase (NAGLU) on chromosome 17q21 results in Sanfilippo B, resulting in excess accumulation of intralysosomal glycosaminoglycans (mucopolysaccharides) in various tissues. We wish to report a novel homozygous variant in a child with features of Sanfilippo syndrome B.

A novel Blind Start study design to investigate vestronidase alfa for mucopolysaccharidosis VII, an ultra-rare genetic disease

BACKGROUND

Drug development for ultra-rare diseases is challenging because small sample sizes and heterogeneous study populations hamper the ability of randomized, placebo-controlled trials with a single primary endpoint to demonstrate valid treatment effects.

METHODS

To overcome these challenges, a novel Blind Start design was utilized in a study of vestronidase alfa in mucopolysaccharidosis VII (Sly syndrome), an ultra-rare lysosomal disease, that demonstrates the strengths of this approach in a challenging drug-development setting. Twelve subjects were randomized to 1 of 4 blinded groups, each crossing over to active treatment in a blinded fashion at different timepoints with efficacy analysis comparing the last assessment before cross over to after 24 weeks of treatment. Study assessments included: Percentage change from baseline in urinary GAG (uGAG); a Multi-Domain Responder Index (MDRI) using prespecified minimal important differences (6-Minute Walk Test, Forced Vital Capacity, shoulder flexion, visual acuity, and Bruininks-Oseretsky Test of Motor Proficiency); fatigue as assessed by the Pediatric Quality of Life Inventory™ Multidimensional Fatigue Scale; and safety.

RESULTS

Vestronidase alfa treatment for 24 weeks significantly reduced uGAG excretion (dermatan sulfate: 64.8%, p < 0.0001). Most subjects (10/12) had a clinically meaningful improvement in at least one MDRI domain with an overall mean change (±SD) of +0.5 (±0.8) at Treatment Week 24 (p = 0.0527). Exposure-adjusted incidence rates of adverse events were similar between groups.

CONCLUSIONS

The Blind Start study and MDRI design improve statistical power that enhances detection of a positive treatment effect in this rare heterogeneous disease and could be utilized for other ultra-rare diseases.

The art and science of choosing efficacy endpoints for rare disease clinical trials

An important challenge in rare disease clinical trials is to demonstrate a clinically meaningful and statistically significant response to treatment. Selecting the most appropriate and sensitive efficacy endpoints for a treatment trial is part art and part science. The types of endpoints should align with the stage of development (e.g., proof of concept vs. confirmation of clinical efficacy). The patient characteristics and disease stage should reflect the treatment goal of improving disease manifestations or preventing disease progression. For rare diseases, regulatory approval requires demonstration of clinical benefit, defined as how a patient, feels, functions, or survives, in at least one adequate and well-controlled pivotal study conducted according to Good Clinical Practice. In some cases, full regulatory approval can occur using a validated surrogate biomarker, while accelerated, or provisional, approval can occur using a biomarker that is likely to predict clinical benefit. Rare disease studies are small by necessity and require the use of endpoints with large effect sizes to demonstrate statistical significance. Understanding the quantitative factors that determine effect size and its impact on powering the study with an adequate sample size is key to the successful choice of endpoints. Interpreting the clinical meaningfulness of an observed change in an efficacy endpoint can be justified by statistical methods, regulatory precedence, and clinical context. Heterogeneous diseases that affect multiple organ systems may be better accommodated by endpoints that assess mean change across multiple endpoints within the same patient rather than mean change in an individual endpoint across all patients.