Mutation analysis in 57 unrelated patients with MPS II (Hunter's disease)

Clinical characteristics and genotypes of 201 patients with mucopolysaccharidosis type II in China: A retrospective, observational study

Mucopolysaccharidosis type II (MPS II) is an X-linked recessive lysosomal storage disease caused by a disease-associated variant in the IDS gene, which encodes iduronate 2-sulfatase (IDS). We aimed to characterize the clinical characteristics and genotypes of the largest cohort of Chinese patients with MPS II and so gain a deeper understanding of natural disease progression. Patients with confirmed MPS II and without treatment were included. The disease was classified as severe in patients with neurological impairment, and as attenuated in patients aged >6 years without neurological impairment. Of the 201 male patients, 78.1% had severe MPS II. Cognitive regression occurred before age 6 years in 94.3% of patients. Of 122 IDS variants identified, 37 were novel. Among the large gene alteration types identified, only the frequency of IDS-IDS2 recombination was significantly higher in severe versus attenuated MPS II (P = 0.032). Some identified point variants could inform the understanding of genotype-phenotype correlations. In conclusion, this study showed that classification of the disease as attenuated should only be made in patients aged >6 years. Our findings expand the understanding of the genotype-phenotype relationship, inform the diagnostic process, and provide an indication of the likely prognosis.

Detection of Structural Variants by NGS: Revealing Missing Alleles in Lysosomal Storage Diseases

Lysosomal storage diseases (LSDs) are a heterogeneous group of rare multisystem metabolic disorders occurring mostly in infancy and childhood, characterized by a gradual accumulation of non-degraded substrates inside the cells. Although biochemical enzymatic assays are considered the gold standard for diagnosis of symptomatic patients, genotyping is a requirement for inclusion in enzyme replacement programs and is a prerequisite for carrier tests in relatives and DNA-based prenatal diagnosis. The emerging next-generation sequencing (NGS) technologies are now offering a powerful diagnostic tool for genotyping LSDs patients by providing faster, cheaper, and higher-resolution testing options, and are allowing to unravel, in a single integrated workflow SNVs, small insertions and deletions (indels), as well as major structural variations (SVs) responsible for the pathology. Here, we summarize the current knowledge about the most recurrent and private SVs involving LSDs-related genes, review advantages and drawbacks related to the use of the NGS in the SVs detection, and discuss the challenges to bring this type of analysis in clinical diagnostics.

Physiology and Pathophysiology of Heparan Sulfate in Animal Models: Its Biosynthesis and Degradation

Heparan sulfate (HS) is a type of glycosaminoglycan that plays a key role in a variety of biological functions in neurology, skeletal development, immunology, and tumor metastasis. Biosynthesis of HS is initiated by a link of xylose to Ser residue of HS proteoglycans, followed by the formation of a linker tetrasaccharide. Then, an extension reaction of HS disaccharide occurs through polymerization of many repetitive units consisting of iduronic acid and N-acetylglucosamine. Subsequently, several modification reactions take place to complete the maturation of HS. The sulfation positions of N-, 2-O-, 6-O-, and 3-O- are all mediated by specific enzymes that may have multiple isozymes. C5-epimerization is facilitated by the epimerase enzyme that converts glucuronic acid to iduronic acid. Once these enzymatic reactions have been completed, the desulfation reaction further modifies HS. Apart from HS biosynthesis, the degradation of HS is largely mediated by the lysosome, an intracellular organelle with acidic pH. Mucopolysaccharidosis is a genetic disorder characterized by an accumulation of glycosaminoglycans in the body associated with neuronal, skeletal, and visceral disorders. Genetically modified animal models have significantly contributed to the understanding of the in vivo role of these enzymes. Their role and potential link to diseases are also discussed.

Genotype-phenotype spectrum of 130 unrelated Indian families with Mucopolysaccharidosis type II

MPS II is an X linked recessive lysosomal storage disorder with multi-system involvement and marked molecular heterogeneity. In this study, we explored the clinical and molecular spectrum of 144 Indian patients with MPS II from 130 unrelated families. Clinical information was collected on a predesigned clinical proforma. Sanger method was employed to sequence all the exons and exon/intron boundaries of the IDS gene. In cases where causative variation was not detected by Sanger sequencing, MLPA and RFLP were performed to identify large deletions/duplications and complex rearrangements. Cytogenetic microarray was done in one patient to see the breakpoints and extent of deletion. In one patient with no detectable likely pathogenic or pathogenic variation, whole-genome sequencing was also performed. Novel variants were systematically assessed by in silico prediction software and protein modelling. The pathogenicity of variants was established based on ACMG criteria. An attempt was also made to establish a genotype-phenotype correlation. Positive family history was present in 31% (41/130) of patients. Developmental delay and intellectual disability were the main reasons for referral. Macrocephaly, coarse facies and dysostosis were present in almost all patients. Hepatosplenomegaly, joint contractures and short stature were the characteristic features, seen in 87% (101/116), 67.8% (74/109) and 41.4% (41/99) patients respectively. Attenuated phenotype was seen in 32.6% (47/144) patients, while severe phenotype was seen in 63% (91/144) patients. The detection rate for likely pathogenic or pathogenic variants in our cohort is 95.5% (107/112) by Sanger sequencing, MLPA and RFLP. We also found two variants of unknown significance, one each by Sanger sequencing and WGS. Total of 71 variants were identified by Sanger sequencing and 29 of these variants were found to be novel. Amongst the novel variants, there was a considerable proportion (51%) of frameshift variants (15/29). Almost half of the causative variants were located in exon 3,8 and 9. A significant genotype-phenotype correlation was also noted for both known and novel variants. This information about the genotype spectrum and phenotype will be helpful for diagnostic and prognostic purposes.

Molecular analysis and novel variation identification of Chinese pedigrees with mucopolysaccharidosis using targeted next-generation sequencing

BACKGROUND

Mucopolysaccharidosis (MPS) refers to a group of lysosomal storage disorders for which seven types and 11 subtypes are currently recognized. Targeted next-generation sequencing (NGS) offers an important method of disease typing, diagnosis, prenatal diagnosis, and treatment.

METHODS

Gene variations in 48 Chinese MPS patients were evaluated using NGS, and the pathogenicity of the DNA alterations was evaluated using PolyPhen2, SIFT, and Mutation Taster. The effect of amino acid substitution on protein structure was also assessed.

RESULTS

Four pedigrees with MPS I (8.3%), 28 with MPS II (58.3%), two with MPS IIIA (4.2%), two with MPS IIIB (4.2%), six with MPS IVA (12.5%), one with MPS IVB (2.1%), and five with MPS VI (10.4%) were identified. Of the 69 variations identified, 11 were novel variants (three in IDUA, five in IDS, and three in GALNS), all of which were predicted to be disease-causing except for one, and were associated with impaired protein structure and function.

CONCLUSIONS

Targeted NGS technology is effective for the gene-based testing of MPS disorders, which show high allelic heterogeneity. MPS II was the predominant form in Chinese. Our study expands the existing variation spectrum of MPS, which is important for disease management and genetic counseling.

Identification and structure characterization of novel IDS variants causing mucopolysaccharidosis type II: A retrospective analysis of 30 Chinese children

BACKGROUND

Mucopolysaccharidosis type II (MPS II) or Hunter syndrome is a rare X-linked recessive genetic disease resulting from deficient activity of the iduronate-2-sulfatase(IDS) enzyme and the accumulation of glycosaminoglycans in almost all cells, tissues and organs, which makes viscera function impaired.This study retrospectively analyzed the clinical characteristics, leukocyte IDS activity and mutations in the IDS gene of 30 Chinese children with MPS II.

METHODS

Whole-exome sequencing (WES) was performed on samples of the 30 patients.

RESULTS

A total of 25 mutations were identified in the IDS genes including 16 previously reported and 9 novel mutations (6 frameshift: c.815-818dupAACG, c.1453dupA, c.1270-1271delGT, c.1484-1485insTA, c.854delA, c.12_13delCC;3missense: c.325 T > G, c.140 T > C, c.248 T > G).The computer simulations of the protein structure analysis of the novel missense mutations showed these amino acid replacements (W109G tryptophan replaced by the glycine, L47P leucine replaced by the proline, V83G valine replaced by glycine) near the active site of IDS protein sulfatase domain and would cause a severe impairment of protein structure and function.

CONCLUSIONS

Our study expands the spectrum of MPS II genotype, provides new insights into the molecular mechanisms of MPS II, and contributes to future studies of genotype-phenotypic associations to estimate prognosis and develop new treatment regimens.

A molecular genetics view on Mucopolysaccharidosis Type II

Mucopolysaccharidosis Type II (MPS II) is an X-linked recessive genetic disorder that primarily affects male patients. With an incidence of 1 in 100,000 male live births, the disease is one of the orphan diseases. MPS II symptoms are caused by mutations in the lysosomal iduronate-2-sulfatase (IDS) gene. The mutations cause a loss of enzymatic performance and result in the accumulation of glycosaminoglycans (GAGs), heparan sulfate and dermatan sulfate, which are no longer degradable. This inadvertent accumulation causes damage in multiple organs and leads either to a severe neurological course or to an attenuated course of the disease, although the exact relationship between mutation, extent of GAG accumulation and disease progression is not yet fully understood. This review is intended to present current diagnostic procedures and therapeutic interventions. In times when the genetic profile of patients plays an increasingly important role in the assessment of therapeutic success and future drug design, we chose to further elucidate the impact of genetic diversity within the IDS gene on disease phenotype and potential implications in current diagnosis, prognosis and therapy. We report recent advances in the structural biological elucidation of I2S enzyme that that promises to improve our future understanding of the molecular damage of the hundreds of IDS gene variants and will aid damage prediction of novel mutations in the future.

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.

Nasal Polyposis in mucopolysaccharidosis type II

Mucopolysaccharidosis (MPS) type II is a rare multisystem disorder resulting from the accumulation of breakdown products of glycosaminoglycans in the body tissues. Many patients with this disease undergo ENT (ear, nose and throat) surgeries such as adenotonsillectomy and tympanocentesis at a very early age, much before the diagnosis of MPS. Nasal polyposis is a rare occurrence, with only one case of MPS II with polyposis reported in the literature. We present a patient who presented with recurrent nasal polyposis from the age of 2 years. Hale's colloidal iron was used to stain these 'nasal polyps', which revealed that they are, in fact, mucopolysaccharide-laden sinonasal mucosa prolapsing into the nasal cavities. We believe this is the first time that this stain has been used to stain nasal polyps in MPS. In addition to the histopathological peculiarities of these nasal masses, we also discuss the natural history of nasal polyposis in MPS II.

Impact of intracerebroventricular enzyme replacement therapy in patients with neuronopathic mucopolysaccharidosis type II

This open-label, phase 1/2 study (JMACCT CTR JMA-IIA00350) evaluated the efficacy and safety of intracerebroventricular idursulfase beta in patients with mucopolysaccharidosis II (MPS II). Herein, we report the 100-week results. Six patients with severe MPS II aged 23-65 months were enrolled. Idursulfase beta (increasing from 1 to 30 mg between weeks 0 and 24, followed by a 30-mg final dose) was administered intracerebroventricularly once every 4 weeks using an implanted cerebrospinal fluid (CSF) reservoir; intravenous administration of idursulfase was also continued throughout the study. Efficacy endpoints included developmental age by the Kyoto Scale of Psychological Development 2001 and heparan sulfate (HS) concentration in CSF (primary outcome). In all six patients, HS concentrations decreased (40%-80%) from baseline to week 100. For overall developmental age, the difference in change from baseline to week 100 in each patient compared with patients treated by intravenous idursulfase administration (n = 13) was +8.0, +14.5, +4.5, +3.7, +8.2, and -8.3 months (mean, +5.1 months). Idursulfase beta was well tolerated. The most common adverse events were pyrexia, upper respiratory tract infection, and vomiting. The results suggest that intracerebroventricular idursulfase beta is well tolerated and can be effective at preventing and stabilizing developmental decline in patients with neuronopathic MPS II.

Mucopolysaccharidosis Type II: A Kenyan Case Series

Hunter syndrome, or mucopolysaccharidosis type 2 (MPS2), is a lysosomal storage disorder associated with the involvement of multiple organs such as the central nervous system, hepatomegaly, musculoskeletal, respiratory, cardiac, and hearing. This is due to the accumulation of glycosaminoglycans in body tissues leading to organ failure. Since the laboratories in Kenya do not screen for metabolic diseases, there is the likelihood of assumption that these patients do not exist. These first cases were referred from the eastern part of Kenya where the majority of inhabitants are from the same ethnic community. It was noted that there was increased mortality among boys below the age of 20 years, and hence, the families sought for help in the national referral and teaching hospital. The case series is meant to show that these cases exist and the majority of the patients may be dying before the diagnosis is made. There are no data on MPS2 from Kenya, and the prevalence and incidence are unknown. In this retrospective study, we present a case series of 6 Kenyan boys with MPS2 from a national referral hospital. They were part of 17 patients who had had their blood analyzed for metabolic diseases. All of them were symptomatic with varying degrees of central nervous system involvement. They had undetectable levels of iduronate-2-sulfatase (I2S) enzyme, and three genetic mutations were detected in the IDS gene.

Effect of Mutated ids Overexpression on IDS Enzyme Activity and Developmental Phenotypes in Zebrafish Embryos: A Valuable Index for Assessing Critical Point-Mutations Associated with Mucopolysaccharidosis Type II Occurrence in Humans

Mucopolysaccharidosis type II (MPS II) is an X-linked disorder resulting from a deficiency in iduronate 2-sulfatase (IDS), which is reported to be caused by gene mutations in the iduronate 2-sulfatase (IDS) gene. Many IDS mutation sites have not yet had their causal relationship with MPS II characterized. We employed a gain-of-function strategy whereby we microinjected different mutated zebrafish ids (z-ids) mRNAs corresponded to human IDS gene into zebrafish embryos, and then measured their total IDS enzymatic activity and observed the occurrence of defective phenotypes during embryonic development. We examined three known mutation sites for human IDS genes (h-IDS) associated with MPS II symptoms, including h-IDS-P86L, -S333L and -R468W, which corresponded to z-ids-P80L, -S327L and -R454W. When these three mutated z-ids mRNAs were overexpressed in zebrafish embryos, the IDS enzymatic activity of the total proteins extracted from the injected embryos was not increased compared with the endogenous IDS of the untreated embryos, which suggests that the IDS enzymatic activity of these three mutated z-ids was totally lost, as expected. Additionally, we observed defective phenotypes in these injected embryos, resulting from the failed IDS enzyme breakdown, which, in turn, has a dominant negative effect on the endogenous wild-type IDS function. These phenotypes were similar to the clinical symptoms observed in MPS II pathogenesis. We further studied six uncharacterized IDS mutation sites as identified by the Taiwanese MPS newborn screening programs. We propose a novel IDS enzyme activity assay combined with phenotypic observation in zebrafish embryos, as an alternative platform for quickly providing a valuable index for preliminarily assessment of any identified IDS point mutation gene that has not yet been characterized, in the context of its role in MPS II development.

Natural history of cognitive development in neuronopathic mucopolysaccharidosis type II (Hunter syndrome): Contribution of genotype to cognitive developmental course

The natural history of cognitive growth in the neuronopathic form of Mucopolysaccharidosis type II (MPS II) is not well defined especially their patterns of development and decline. The ability to predict the developmental course of the neurologically impaired patient is necessary to assess treatment outcomes aimed at the brain. Thirteen intravenous enzyme replacement therapy-treated Japanese patients with neuronopathic MPSII who had mutation analysis were followed on one standard measure of cognitive development over time. Six children in Group MS had missense mutations and 7 children in Group NT had null type mutations such as deletions, recombination with the pseudogene, and nonsense mutations. The patients as a whole demonstrated cognitive growth until about 36-42 months of age, followed by a plateau in development. The mean age equivalent score at age 3 was similar to that at age 6. While the decline was slow for the entire group, the patients in Group NT showed a more rapid decline than those in Group MS. Two patients with deletions showed decline to a very low level by age 5. The long plateau in cognitive development in patents with MPS II was substantiated and was consistent with other studies. This is the first demonstration that different mutation types within the neuronopathic MPS II patients are associated with different rates of decline. We also were able to identify the chronological age before which a trial would need to start in order to maintain cognitive growth and a ceiling beyond which a relatively normal outcome would not be likely.

Endoplasmic Reticulum and Lysosomal Quality Control of Four Nonsense Mutants of Iduronate 2-Sulfatase Linked to Hunter's Syndrome

Hunter's syndrome (mucopolysaccharidosis type II) is a rare X-linked lysosomal storage disorder caused by mutations in the iduronate-2-sulfatase (IDS) gene. Motivated by the case of a child affected by this syndrome, we compared the intracellular fate of wild-type IDS (IDS_WT) and four nonsense mutations of IDS (IDS_L482X, IDS_Y452X, IDS_R443X, and IDS_W337X) generating progressively shorter forms of IDS associated with mild to severe forms of the disease. Our analyses revealed formylation of all forms of IDS at cysteine 84, which is a prerequisite for enzymatic activity. After formylation, IDS_WT was transported within lysosomes, where it was processed in the mature form of the enzyme. The length of disease-causing deletions correlated with gravity of the folding and transport phenotype, which was anticipated by molecular dynamics analyses. The shortest form of IDS, IDS_W337X, was retained in the endoplasmic reticulum (ER) and degraded by the ubiquitin-proteasome system. IDS_R443X, IDS_Y452X, and IDS_L482X passed ER quality control and were transported to the lysosomes, but failed lysosomal quality control, resulting in their rapid clearance and in loss-of-function phenotype. Failure of ER quality control inspection is an established cause of loss of function observed in protein misfolding diseases. Our data reveal that fulfillment of ER requirements might not be sufficient, highlight lysosomal quality control as the distal station to control lysosomal enzymes fitness and pave the way for alternative therapeutic interventions.

Identification and Functional Characterization of IDS Gene Mutations Underlying Taiwanese Hunter Syndrome (Mucopolysaccharidosis Type II)

Hunter syndrome (mucopolysaccharidosis II; MPS II) is caused by a defect of the iduronate-2-sulfatase (IDS) gene. Few studies have reported integrated mutation data of Taiwanese MPS II phenotypes. In this study, we summarized genotype and phenotype correlations of confirmed MPS II patients and asymptomatic MPS II infants in Taiwan. Regular polymerase chain reaction and DNA sequencing were used to identify genetic abnormalities of 191 cases, including 51 unrelated patients with confirmed MPS II and 140 asymptomatic infants. IDS activity was analyzed in individual novel IDS variants using in vitro expression studies. Nineteen novel mutations were identified, in which the percentages of IDS activity of the novel missense mutations c.137A>C, c.311A>T, c.454A>C, c.797C>G, c.817C>T, c.998C>T, c.1106C>G, c.1400C>T, c.1402C>T, and c.1403G>A were significantly decreased (p < 0.001), c.254C>T and c.1025A>G were moderately decreased (p < 0.01), and c.851C>T was slightly decreased (p < 0.05) comparing with normal enzyme activity. The activities of the other six missense mutations were reduced but were insignificant. The results of genomic studies and their phenotypes were highly correlated. A greater understanding of the positive correlations may help to prevent the irreversible manifestations of Hunter syndrome, particularly in infants suspected of having asymptomatic MPS II. In addition, urinary glycosaminoglycan assay is important to diagnose Hunter syndrome since gene mutations are not definitive (could be non-pathogenic).

Molecular diagnosis of patients affected by mucopolysaccharidosis: a multicenter study

Mucopolysaccharidoses (MPS) are a subgroup of 11 monogenic lysosomal storage disorders due to the deficit of activity of the lysosomal hydrolases deputed to the degradation of mucopolysaccharides. Although individually rare, all together they account for at least 1:25,000 live births. In this study, we present the genetic analysis of a population of 71 MPS patients enrolled in a multicenter Italian study. We re-annotated all variants, according to the latest recommendations, and re-classified them as suggested by the American College of Medical Genetics and Genomics. Variant distribution per type was mainly represented by missense mutations. Overall, 10 patients had received no molecular diagnosis, although 6 of them had undergone either HSCT or ERT, based on clinical and enzymatic evaluations. Moreover, nine novel variants are reported.Conclusions: Our analysis underlines the need to complete the molecular diagnosis in patients previously diagnosed only on a biochemical basis, suggests a periodical re-annotation of the variants and solicits their deposition in public databases freely available to clinicians and researchers. We strongly recommend a molecular diagnosis based on the analysis of the "trio" instead of the sole proband. These recommendations will help to obtain a complete and correct diagnosis of mucopolysaccharidosis, rendering also possible genetic counseling. What is known • MPS are a group of 11 metabolic genetic disorders due to deficits of enzymes involved in the mucopolysaccharides degradation. • Molecular analysis is commonly performed to confirm enzymatic assays. What is new • Eighty-six percent of the 71 patients we collected received a molecular diagnosis; among them, 9 novel variants were reported. • We stress the importance of molecular diagnosis in biochemically diagnosed patients, encourage a periodical re-annotation of variants according to the recent nomenclature and their publication in open databases.

Validation of the shortened Hunter Syndrome-Functional Outcomes for Clinical Understanding Scale (HS-FOCUS)

Background

The rare disease, Hunter Syndrome (mucopolysaccharidosis type II; MPS II), characterized by iduronate-2-sulfatase deficiency, has heterogeneous symptoms often including cognitive impairment (CI). To evaluate physical functioning and daily activity limitations of patients with MPS II, the multidomain shortened Hunter Syndrome-Functional Outcomes for Clinical Understanding Scale (HS-FOCUS) questionnaire was previously developed and preliminarily validated. Here we gather data in a dedicated prospective longitudinal observational study using direct responses to the shortened instrument and assess its psychometric properties further.

Methods

Interview data were collected from eligible self-reporting patients (≥ 12 years of age) or caregivers of patients using respective versions of the instrument at baseline and 2–4 weeks later. Internal consistency, test–retest reliability, convergent and discriminant validity, and validity of known groups were assessed. Participants also completed Child Health Questionnaire (CHQ), Health Utilities Index Mark 3, and Global Impression of Severity (GIS) questionnaires.

Results

All patients were male, consisting of 31 caregiver-reported patients (aged 3–26 years) and 20 self-reported patients (aged 12–58 years). Most (77.4%) caregiver-reported patients had CI. Both questionnaire versions demonstrated good internal consistency and test–retest reliability; Cronbach’s alpha and intra-class correlation coefficients were > 0.70. Spearman’s correlations demonstrated good convergent validity with moderate (> 0.3) to high (> 0.6) correlations of the HS-FOCUS total score with physical functioning, role/social–physical, and bodily pain domains of CHQ. The tool also differentiated between MPS II severity levels based on GIS scores.

Conclusions

The shortened HS-FOCUS questionnaire was found to be a valid and reliable tool to assess the physical functioning impact of MPS II.

Comparative studies of vertebrate iduronate 2-sulfatase (IDS) genes and proteins: evolution of A mammalian X-linked gene

IDS is responsible for the lysosomal degradation of heparan sulfate and dermatan sulfate and linked to an X-linked lysosomal storage disease, mucopolysaccharidosis 2 (MPS2), resulting in neurological damage and early death. Comparative IDS amino acid sequences and structures and IDS gene locations were examined using data from several vertebrate genome projects. Vertebrate IDS sequences shared 60–99% identities with each other. Human IDS showed 47% sequence identity with fruit fly (Drosophila melanogaster) IDS. Sequence alignments, key amino acid residues, N-glycosylation sites and conserved predicted secondary and tertiary structures were also studied, including signal peptide, propeptide and active site residues. Mammalian IDS genes usually contained 9 coding exons. The human IDS gene promoter contained a large CpG island (CpG46) and 5 transcription factor binding sites, whereas the 3′-UTR region contained 5 miRNA target sites. These may contribute to IDS gene regulation of expression in the brain and other neural tissues of the body. An IDS pseudogene (IDSP1) was located proximally to the IDS gene on the X-chromosome in primate genomes. Phylogenetic analyses examined the relationships and potential evolutionary origins of the vertebrate IDS gene. These suggested that IDS has originated in an invertebrate ancestral genome and retained throughout vertebrate evolution and conserved on marsupial and eutherian X-chromosomes, with the exception of rat Ids on chromosome 8.

Clinical, biochemical and molecular characteristics of Filipino patients with mucopolysaccharidosis type II - Hunter syndrome

BACKGROUND

Mucopolysaccharidosis type II, an X-linked recessive disorder is the most common lysosomal storage disease detected among Filipinos. This is a case series involving 23 male Filipino patients confirmed to have Hunter syndrome. The clinical and biochemical characteristics were obtained and mutation testing of the IDS gene was done on the probands and their female relatives.

RESULTS

The mean age of the patients was 11.28 (SD 4.10) years with an average symptom onset at 1.2 (SD 1.4) years. The mean age at biochemical diagnosis was 8 (SD 3.2) years. The early clinical characteristics were developmental delay, joint stiffness, coarse facies, recurrent respiratory tract infections, abdominal distention and hernia. Majority of the patients had joint contractures, severe intellectual disability, error of refraction, hearing loss and valvular regurgitation on subspecialists' evaluation. The mean GAG concentration was 506.5 mg (SD 191.3)/grams creatinine while the mean plasma iduronate-2-sulfatase activity was 0.86 (SD 0.79) nmol/mg plasma/4 h. Fourteen (14) mutations were found: 6 missense (42.9%), 4 nonsense (28.6%), 2 frameshift (14.3%), 1 exon skipping at the cDNA level (7.1%), and 1 gross insertion (7.1%). Six (6) novel mutations were observed (43%): p.C422F, p.P86Rfs*44, p.Q121*, p.L209Wfs*4, p.T409R, and c.1461_1462insN[710].

CONCLUSION

The age at diagnosis in this series was much delayed and majority of the patients presented with severe neurologic impairment. The results of the biochemical tests did not contribute to the phenotypic classification of patients. The effects of the mutations were consistent with the severe phenotype seen in the majority of the patients.

Clinical and Genetic Characteristics of Romanian Patients with Mucopolysaccharidosis Type II

BACKGROUND

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is a rare X-linked disorder caused by deficiency of iduronate-2-sulfatase (I2S) enzyme, which leads to the accumulation of partially digested glycosaminoglycans (GAGs) in the lysosomes and induces multisystemic alteration (coarse facial features; skeletal dysplasia; hepatosplenomegaly; joint stiffness and contractures; heart, lung, vision, and hearing disability; profound neurological decline).The purpose of this study is to present the clinical and genetic characteristics of Romanian patients with Hunter syndrome and the genotype-phenotype correlation.

MATERIAL AND METHODS

15 unrelated patients, with MPS II ranging from mild (4 subjects) to severe phenotype (11 subjects) aged 2 to 20 years, were evaluated clinically, cognitive development, enzyme assay and molecular analysis.

RESULTS

The molecular analysis of the 15 unrelated Romanian MPS II patients has identified 15 different mutations (2 major genetic defects (13%) and 13 minor genetic defects (87%)): microdeletions and point mutations (missense, nonsense), seven of them described for the first time-deletion encompassing 3 to exon 7; c823G>T, pD275Y; c.1600A>C (pN534H); c.102_10delAG (p.D5Cfs*11); c.448_471del (p.P150_P157del); c.421delA (p.I141Yfs*72); and c.419-1G>C. The major genetic defects were correlated with a severe course of disease.

CONCLUSION

This is the first study on the clinical and molecular characterization of the MPS II Romanian patients. This study supports the evidence of the mutational heterogeneity of the I2S gene as well as the difficulty to correlate genotype and phenotype in the patients with MPS II.

Molecular diagnosis of 65 families with mucopolysaccharidosis type II (Hunter syndrome) characterized by 16 novel mutations in the IDS gene: Genetic, pathological, and structural studies on iduronate-2-sulfatase

Mucopolysaccharidosis type II (MPS II: also called as Hunter syndrome) is an X-linked recessive lysosomal storage disorder characterized by the accumulation of extracellular glycosaminoglycans due to the deficiency of the enzyme iduronate-2-sulfatase (IDS). Previous observations suggested that MPS II can be classified into two distinct disease subtypes: (1) severe type of MPS II involves a decline in the cognitive ability of a patient and (2) attenuated type of MPS II exhibits no such intellectual phenotype. To determine whether such disease subtypes of MPS II could be explained by genetic diagnosis, we analyzed mutations in the IDS gene of 65 patients suffering from MPS II among the Japanese population who were diagnosed with both the accumulation of urinary glycosaminoglycans and a decrease in their IDS enzyme activity between 2004 and 2014. Among the specimens examined, we identified the following mutations: 33 missense, 8 nonsense, 7 frameshift, 4 intronic changes affecting splicing, 8 recombinations involving IDS-IDS2, and 7 other mutations including 4 large deletions. Consistent with the previous data, the results of our study showed that most of the attenuated phenotype was derived from the missense mutations of the IDS gene, whereas mutations associated with a large structural alteration including recombination, splicing, frameshift, and nonsense mutations were linked to the severe phenotype of MPS II. Furthermore, we conducted a homology modeling study of IDS P120R and N534I mutant as representatives of the causative mutation of the severe and attenuated type of MPS II, respectively. We found that the substitution of P120R of the IDS enzyme was predicted to deform the α-helix generated by I119-F123, leading to the major structural alteration of the wild-type IDS enzyme. In sharp contrast, the effect of the structural alteration of N534I was marginal; thus, this mutation was pathogenically predicted to be associated with the attenuated type of MPS II. These results suggest that a combination of the genomic diagnosis of the IDS gene and the structural prediction of the IDS enzyme could enable the prediction of a phenotype more effectively.

Deep Genotyping of the IDS Gene in Colombian Patients with Hunter Syndrome

BACKGROUND

Mucopolysaccharidosis type II (MPSII), also known as Hunter syndrome, is an X-linked disorder caused by mutations in the iduronate 2 sulfatase (IDS) gene. This enzyme catalyzes the initial step in the catabolism of heparan sulfate and dermatan sulfate; thus, its deficiency leads to the accumulation of these glycosaminoglycans. MPS II has significant allelic heterogeneity, making the establishment of genotype-phenotype correlations difficult. This study assessed clinical features in combination with deep genotyping of a group of Colombian patients with MPS II and attempted to establish a degree of genotype-phenotype correlation by employing bioinformatic tools.

METHODS

Eighteen patients were included in this study, 11% of whom were non-neuronopathic, and the other 89% were neuronopathic. Samples were all analyzed using three molecular methodologies: MLPA, direct exon sequencing, and RFLP analysis.

RESULTS

A total of 13 mutations were identified, 6 of which were novel (c.548_564dup16, c.477insT, c.595_607del12, c. 549_562del13, c.182delC, and a complete deletion of exon 7). The frequency of common mutations (R468Q, Q465X, K347Q, K236N, S71N, R88H, and a conversion phenomenon) was 53.85%. The S71N mutation was frequent among the attenuated phenotype, while private frameshift mutations and rearrangements were seen in patients with severe phenotypes. Molecular docking was performed on the wild-type and mutant IDS proteins, which revealed changes in the enzyme-substrate interaction for the mutant IDS.

CONCLUSION

The frequency of novel mutations (46.15%) is similar to what has been reported elsewhere. The use of bioinformatic tools showed differences in enzyme-substrate interactions. Studies with larger groups of patients are needed.

Enzyme Replacement Therapy in Mucopolysaccharidosis II Patients Under 1 Year of Age

Mucopolysaccharidosis (MPS) II, or Hunter syndrome, is a lysosomal storage disease characterized by multi-systemic involvement and a progressive clinical course. Enzyme replacement therapy with idursulfase has been approved in more than 50 countries worldwide; however, safety and efficacy data from clinical studies are currently only available for patients 1.4 years of age and older. Sibling case studies of infants with MPS I, II, and VI who initiated ERT in the first weeks or months of life have reported no new safety concerns and a more favorable clinical course for the sibling treated in infancy than for the later-treated sibling. Here we describe our experiences with a case series of eight MPS II patients for whom idursulfase treatment was initiated at under 1 year of age. The majority of the patients were diagnosed because of a family history of disease. All of the infants displayed abnormalities consistent with MPS II at diagnosis. The youngest age at treatment start was 10 days and the oldest was 6.5 months, with duration of treatment varying between 6 weeks and 5.5 years. No new safety concerns were observed, and none of the patients experienced an infusion-related reaction. All of the patients treated for more than 6 weeks showed improvements and/or stabilization of some somatic manifestations while on treatment. In some cases, caregivers made comparisons with other affected family members and reported that the early-treated patients experienced a less severe clinical course, although a lack of medical records for many family members precluded a rigorous comparison.

Genetic analysis of 17 children with Hunter syndrome: identification and functional characterization of four novel mutations in the iduronate-2-sulfatase gene

Mucopolysaccharidosis type II (MPS II) is a rare X-linked disorder caused by alterations in the iduronate-2-sulfatase (IDS) gene. In this study, IDS activity in peripheral mononuclear blood monocytes (PMBCs) was measured with a fluorimetric enzyme assay. Urinary glycosaminoglycans (GAGs) were quantified using a colorimetric assay. All IDS exons and intronic flanks were bidirectionally sequenced. A total of 15 mutations (all exonic region) were found in 17 MPS II patients. In this cohort of MPS II patients, all alterations in the IDS gene were caused by point nucleotide substitutions or small deletions. Mutations p.Arg88His and p.Arg172* occurred twice. All mutations were inherited except for p.Gly489Alafs*7, a germline mutation. We found four new mutations (p.Ser142Phe, p.Arg233Gly, p.Glu430*, and p.Ile360Tyrfs*31). In Epstein-Barr virus (EBV)-immortalized PMBCs derived from the MPS II patients, no IDS protein was detected in case of the p.Ser142Phe and p.Ile360Tyrfs*31 mutants. For p.Arg233Gly and p.Glu430*, we observed a residual expression of IDS. The p.Arg233Gly and p.Glu430* mutants had a residuary enzymatic activity that was lowered by 14.3 and 76-fold, respectively, compared with healthy controls. This observation may help explain the mild disease phenotype in MPS II patients who had these two mutations whereas the p.Ser142Phe and p.Ile360Tyrfs*31 mutations caused the severe disease manifestation.

Mucopolysaccharidosis type II: identification of 30 novel mutations among Latin American patients

In this study, 103 unrelated South-American patients with mucopolysaccharidosis type II (MPS II) were investigated aiming at the identification of iduronate-2-sulfatase (IDS) disease causing mutations and the possibility of some insights on the genotype-phenotype correlation The strategy used for genotyping involved the identification of the previously reported inversion/disruption of the IDS gene by PCR and screening for other mutations by PCR/SSCP. The exons with altered mobility on SSCP were sequenced, as well as all the exons of patients with no SSCP alteration. By using this strategy, we were able to find the pathogenic mutation in all patients. Alterations such as inversion/disruption and partial/total deletions of the IDS gene were found in 20/103 (19%) patients. Small insertions/deletions/indels (<22 bp) and point mutations were identified in 83/103 (88%) patients, including 30 novel mutations; except for a higher frequency of small duplications in relation to small deletions, the frequencies of major and minor alterations found in our sample are in accordance with those described in the literature.

Mucopolysaccharidosis type II in females and response to enzyme replacement therapy

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is an X-linked lysosomal storage disease caused by a deficiency of iduronate-2-sulfatase (IDS). Two affected girls with moderate and severe forms of MPS II with normal karyotypes and increased urinary dermatan sulphate and heparin sulphate excretion and marked deficiencies of IDS activity are reported. Molecular studies showed that case 1 has a heterozygous mutation c.1568A > G (p.Y523C) associated with almost totally skewed inactivation of the normal maternal X chromosome, and case 2 has a heterozygous deletion that includes exons 1-4 of IDS (minimal deletion range c.1-103_184del). The multi-exon deletion correlated with early onset of the disease and severe phenotype with intellectual disability, whereas the missense mutation was associated with moderate developmental delay. Although genotype-phenotype correlation in MPS II is difficult, gene deletions seem to correlate with more severe clinical manifestation of the disease. Enzyme replacement therapy (ERT) in these two females resulted in disease stabilization in both.

The role of enzyme replacement therapy in severe Hunter syndrome-an expert panel consensus

Intravenous enzyme replacement therapy (ERT) with idursulfase for Hunter syndrome has not been demonstrated to and is not predicted to cross the blood-brain barrier. Nearly all published experience with ERT with idursulfase has therefore been in patients without cognitive impairment (attenuated phenotype). Little formal guidance is available on the issues surrounding ERT in cognitively impaired patients with the severe phenotype. An expert panel was therefore convened to provide guidance on these issues. The clinical experience of the panel with 66 patients suggests that somatic improvements (e.g., reduction in liver volume, increased mobility, and reduction in frequency of respiratory infections) may occur in most severe patients. Cognitive benefits have not been seen. It was agreed that, in general, severe patients are candidates for at least a 6-12-month trial of ERT, excluding patients who are severely neurologically impaired, those in a vegetative state, or those who have a condition that may lead to near-term death. It is imperative that the treating physician discuss the goals of treatment, methods of assessment of response, and criteria for discontinuation of treatment with the family before ERT is initiated.

CONCLUSION

The decision to initiate ERT in severe Hunter syndrome should be made by the physician and parents and must be based on realistic expectations of benefits and risks, with the understanding that ERT may be withdrawn in the absence of demonstrable benefits.

Analysis of the IDS gene in 38 patients with Hunter syndrome: the c.879G>A (p.Gln293Gln) synonymous variation in a female create exonic splicing

Background

Hunter syndrome (mucopolysaccharidosis type II, MPS II) is a rare disease inherited in an X-linked autosomal recessive pattern. It is the prevailing form of the mucopolysaccharidoses in China. Here we investigated mutations of IDS (iduronate 2-sulfatase) gene in 38 unrelated Chinese patients, one of which is a female.

Methods

Peripheral leucocytes were collected from the patients and the IDS gene was amplified to looking for the variations. For a female patient, the X chromosome status was analyzed by androgen receptor X-inactivation assay and the mutation impact on RNA level was further performed by reverse transcription polymerase chain reaction.

Results

We discovered that point mutations constituted the major form while mutations in codon p.R468 defined the largest number of patients in our cohort. Consistent with data from other ethnic groups, exons 9 and 3 had comparatively more mutations, while exon 2 had quite a few mutations unique to Chinese patients. Of the 30 different mutations identified, only 9 were novel: one was a premature termination mutation, i.e., c.196C>T (p.Gln66X); three were missense mutations, i.e., c.200T>C (p.Leu67Pro), c.215T>C (p.Leu72Pro), c.389C>T (p.Thr130Ile); one was a small deletion, i.e., c.1104_1122del19 (p.Ser369ArgfsX16); and one was a deletion that spanned both exons 8 and 9 deletion leading to gross structural changes in the IDS gene. In addition, a synonymous mutation c.879G>A (p.Gln293Gln) was identified in a female Hunter disease patient, which resulted in loss of the original splicing site, activated a cryptic splicing site upstream, leading to a 28 bp deletion and a premature termination at p. Tyr285GlufsX47. Together with concurrent skewed X-inactivation this was believed to facilitate the development of Hunter disease in this girl.

Conclusions

In conclusion, the molecular analysis of IDS gene in Chinese patients confirmed the Hunter disease diagnosis and expanded the mutation and clinical spectrum of this devastating disorder.

Preventing mucopolysaccharidosis type II (Hunter syndrome): PGD and establishing a Hunter (46, XX) stem cell line

OBJECTIVES

Preimplantation genetic diagnosis (PGD) enables the identification of affected embryos prior to implantation. We present for the first time three families in which either the oocytes or embryos obtained from female carriers of mutations in the iduronate-2-sulfatase (IDS) gene underwent PGD for mucopolysaccharidosis type II (Hunter syndrome). Furthermore, we report the first ever derivation of a Hunter's syndrome (46, XX) human stem cell line from embryos (HESC) carrying the IDS and oculocutaneus albinism type 2 mutations.

METHODS

Combined polar body (PB) 1 and 2 or a single cell of a six- to eight-cell embryo (blastomere) was used for genetic analysis by multiplex polymerase chain reaction assay using six microsatellite polymorphic markers flanking the gene and mutation.

RESULTS

One couple underwent four PB-PGD cycles, with birth of a healthy girl; the second couple with one PB-PGD cycle had healthy twins; the third couple underwent seven cycles of double PGD for Hunter and Albinism syndrome with birth of healthy twins. One novel Hunter 46, XX HESC line was established displaying typical characteristics of HESC cells.

CONCLUSIONS

PGD is a reliable method to prevent pregnancy of children affected with Hunter syndrome. In addition, derived HESC can be further utilized for drug testing and better understanding of the pathogenesis of this syndrome.

Natural progression of neurological disease in mucopolysaccharidosis type II

OBJECTIVE

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder characterized by insufficiency of the iduronate-2-sulfatase enzyme, which results in excess heparan and dermatan sulfates within the lysosomes of various tissues and organs, including the central nervous system. The purpose of this study was to investigate the natural progression of neurologic disease in a large cohort of patients evaluated with standardized testing at a single institution.

METHODS

During the period of December 2002 to October 2010, patients with MPS II were referred to the Program for Neurodevelopmental Function in Rare Disorders. A retrospective review of patient data was performed, which included the use of detailed questionnaires that addressed medical history, notes from previous health care providers, and the results of a multidisciplinary evaluation that lasted 4 to 6 hours and was performed by a team of neurodevelopmental pediatricians, speech pathologists, psychologists, audiologists, psychometricians, and occupational and physical therapists. Patients were evaluated annually for management of disease progression.

RESULTS

A total of 50 male patients with MPS II were evaluated over 152 encounters. Two distinct subgroups of children were identified. One subset of patients had normal cognitive, speech and language, and adaptive functions whereas the other showed a dramatic decline in these areas. All patients developed fine and gross motor deficits.

CONCLUSION

The natural progression of MPS II manifests as 2 divergent and distinct neurologic phenotypes with similar somatic disease. Patients may have primary neural parenchymal disease with cognitive involvement or may maintain normal cognitive abilities.

Identification of 11 novel mutations in 49 Korean patients with mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) or Hunter syndrome is a rare lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase (IDS). As MPS II is X-linked, patients are usually males with heterogeneous mutations ranging from point mutations to gross deletions and recombination. In 2003, we reported a mutation analysis of 25 patients with MPS II. In this study, 31 mutations in another 49 Korean patients (45 families) with MPS II are reported: 12 missense, nine deletions, four splicing, two nonsense, two insertions, one deletion/insertion, and IDS-IDS2 recombination mutations. Among these mutations, 11 were novel ones (4 missense mutations: Ser61Pro, Pro97Arg, Pro228Ala, and Pro261Ala; 5 deletions: c.344delA, c.420delG, c.768delT, c.1112delC and c.1402delC; 1 deletion/insertion: c.1222delinsTA; and 1 insertion mutation: c.359_360insATCC). The IDS-IDS2 recombination mutations were most frequently observed; all patients with this mutation had the severe MPS II phenotype. However, most of the patients (5/7) with the G374G splicing mutation had an attenuated phenotype, except for two sibling cases with the severe phenotype. Except for a few recurrent mutations such as the G374G, R443X, L522P, and recombination mutations, each patient had a unique individual mutation. Therefore, careful interpretation of genotype-phenotype correlations is warranted.

Female Hunter syndrome caused by a single mutation and familial XCI skewing: implications for other X-linked disorders

Familial X-chromosome inactivation (XCI) skewing was investigated in a family in which a female mucopolysaccharidosis type II (MPS II) (Hunter syndrome, an X-linked genetic disease) occurred. Among eight related females aged under 60 years from three generations who were tested, four revealed a non-random pattern of XCI. Detailed genetic analysis failed to find mutations in genes that were previously reported as important for the XCI process. Haplotype analysis excluded linkage of non-random XCI with genes localized on the X-chromosome. We propose that analysis of the XCI pattern should be taken into consideration when assessing risk factors for X-linked recessive genetic disorders.

Correction of CNS defects in the MPSII mouse model via systemic enzyme replacement therapy

Mucopolysaccharidosis type II (MPSII), or Hunter syndrome, is a devastating disorder associated with a shortened life expectancy. Patients affected by MPSII have a variety of symptoms that affect all organs of the body and may include progressive cognitive impairment. MPSII is due to inactivity of the enzyme iduronate-2-sulfatase (IDS), which results in the accumulation of storage material in the lysosomes, such as dermatan and heparan sulfates, with consequent cell degeneration in all tissues including, in the severe phenotype, neurodegeneration in the central nervous system (CNS). To date, the only treatment available is systemic infusion of IDS, which ameliorates exclusively certain visceral defects. Therefore, it is important to simultaneously treat the visceral and CNS defects of the MPSII patients. Here, we have developed enzyme replacement therapy (ERT) protocols in a mouse model that allow the IDS to reach the brain, with the substantial correction of the CNS phenotype and of the neurobehavioral features. Treatments were beneficial even in adult and old MPSII mice, using relatively low doses of infused IDS over long intervals. This study demonstrates that CNS defects of MPSII mice can be treated by systemic ERT, providing the potential for development of an effective treatment for MPSII patients.

Japan Elaprase Treatment (JET) study: idursulfase enzyme replacement therapy in adult patients with attenuated Hunter syndrome (Mucopolysaccharidosis II, MPS II)

This open-label clinical study enrolled 10 adults with attenuated Mucopolysaccharidosis II and advanced disease under the direction of the Japan Society for Research on Mucopolysaccharidosis Disorders prior to regulatory approval of idursulfase in Japan. Ten male patients, ages 21-53 years, received weekly intravenous infusions of 0.5 mg/kg idursulfase for 12 months. Significant reductions in lysosomal storage and several clinical improvements were observed during the study (mean changes below). Urinary glycosaminoglycan excretion decreased rapidly within the first three months of treatment and normalized in all patients by study completion (-79.9%). Liver and spleen volumes also showed rapid reductions that were maintained in all patients through study completion (-33.2% and -31.0%, respectively). Improvements were noted in the 6-Minute Walk Test (54.5 m), percent predicted forced vital capacity (3.8 percentage points), left ventricular mass index (-12.4%) and several joint range of motions (8.1-19.0 degrees). Ejection fraction and cardiac valve disease were stable. The sleep study oxygen desaturation index increased by 3.9 events/h, but was stable in 89% (8/9) of patients. Idursulfase was generally well-tolerated. Infusion-related reactions occurred in 50% of patients and were mostly mild with transient skin reactions that did not require medical intervention. Two infusion-related reactions were assessed as serious (urticaria and vasovagal syncope). One patient died of causes unrelated to idursulfase. Anti-idursulfase antibodies developed in 60% (6/10) of patients. In summary, idursulfase treatment appears to be safe and effective in adult Japanese patients with attenuated MPS II. These results are comparable to those of prior studies that enrolled predominantly pediatric, Caucasian, and less ill patients. No new safety risks were identified.

Multidisciplinary management of Hunter syndrome

Hunter syndrome is a rare, X-linked disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase. In the absence of sufficient enzyme activity, glycosaminoglycans accumulate in the lysosomes of many tissues and organs and contribute to the multisystem, progressive pathologies seen in Hunter syndrome. The nervous, cardiovascular, respiratory, and musculoskeletal systems can be involved in individuals with Hunter syndrome. Although the management of some clinical problems associated with the disease may seem routine, the management is typically complex and requires the physician to be aware of the special issues surrounding the patient with Hunter syndrome, and a multidisciplinary approach should be taken. Subspecialties such as otorhinolaryngology, neurosurgery, orthopedics, cardiology, anesthesiology, pulmonology, and neurodevelopment will all have a role in management, as will specialty areas such as physiotherapy, audiology, and others. The important management topics are discussed in this review, and the use of enzyme-replacement therapy with recombinant human iduronate-2-sulfatase as a specific treatment for Hunter syndrome is presented.

Molecular analysis of the iduronate-2-sulfatase gene in Thai patients with Hunter syndrome

Molecular defects in the gene encoding the enzyme iduronate-2-sulfatase (IDS) result in Hunter disease (mucopolysaccharidosis type II, MPS II). To determine the molecular basis of MPS II in Thailand, the IDS gene was analysed in 20 Thai patients with Hunter syndrome from 18 unrelated families. A total of 19 different mutations, including 9 missense mutations, 3 nonsense mutations, 3 splice site alterations, 1 deletion, 2 indels, and 1 rearrangement were identified, 8 of which were novel (p.R101C, p.D148V, p.G224A, p.K227E, p.E254X, p.W337X, c.440_442delinsTT and c.720_731delinsTTTCAGATGTTCTCCCCAG). Evaluation of the IDS activity of two hemizygous variants identified in the same patient, p.R101C and p.R468Q, by expression of IDS with the individual mutations in COS 7 cells indicated that only the p.R468Q mutation affected IDS protein activity. Two exonic mutations, c.257C>T (p.P86L) and c.418G>A, were found to activate multiple cryptic splice sites, resulting in aberrantly spliced transcripts. Thus, MPS II in Thailand is caused by a diverse set of defects affecting both IDS protein production and activity.

Initial report from the Hunter Outcome Survey

PURPOSE

Hunter syndrome (Mucopolysaccharidosis II) is a rare, X-linked disorder of glycosaminoglycan metabolism. It is caused by a deficiency in the lysosomal enzyme iduronate-2-sulfatase, and in affected patients glycosaminoglycan accumulates in lysosomes of various tissues and organs and contributes to the pathophysiology of Hunter syndrome. The Hunter Outcome Survey (HOS) was established to better describe the natural history of this disorder and to evaluate the long-term effect of enzyme replacement therapy.

METHODS

HOS is an international, multicenter, long-term observational survey that will collect data on participating patients with a confirmed diagnosis of Hunter syndrome. Data will be collected during regular physician examinations and entered into an electronic database. Examples of observations include vital signs, laboratory values, signs and symptoms of organ involvement, and the results of selected functional tests (e.g., audiometry, echocardiogram, joint mobility, etc.).

RESULTS

As of May 15, 2007, 263 patients from 16 countries have enrolled in HOS; 24% of these patients were currently being treated with enzyme replacement therapy. The median age at enrollment was 12.2 years. The median age of onset of symptoms and diagnosis of Hunter syndrome were 1.5 and 3.5 years, respectively. Otitis media and abdominal hernia were the earliest presenting symptoms. Facial dysmorphism and hepatosplenomegaly were demonstrated by 95% and 89% of patients, respectively.

CONCLUSIONS

HOS will be a valuable resource for enhancing the understanding of Hunter syndrome and will provide important information about the natural history of the disease and the role of enzyme replacement therapy in its treatment. Patients and their physicians should be encouraged to participate.

Review of the use of idursulfase in the treatment of mucopolysaccharidosis II

Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is a heterogeneous, progressive X-linked recessively inherited lysosomal storage disease that is caused by a deficiency of the enzyme iduronate-2-sulfatase, resulting in abnormal tissue accumulation of the glycosaminoglycans, dermatan sulfate and heparan sulfate. The disorder results from mutations in IDS, which is located at Xq28. Over 300 pathogenic mutations have been identified to date. The management of MPS II requires multidisciplinary care because of the many affected organ systems. Replacement of functional enzyme to involved tissues has been a focus of various therapies for several decades. The transplantation of hematopoietic stem cells provides enzymatic reconstitution in many target tissues, but the clinical response has been disappointing. Recently, enzyme replacement therapy with recombinant human iduronate-2-sulfatase (idursulfase, Elaprase((R)); Shire HGT Pharmaceuticals, Cambridge MA, USA), was approved by the in the US and Europe as a safe and effective treatment for individuals with MPS II. This review presents a comprehensive overview of MPS II and summarizes the recent literature on therapy for the disease.

Recognition and diagnosis of mucopolysaccharidosis II (Hunter syndrome)

Mucopolysaccharidosis II, also known as Hunter syndrome, is a rare, X-linked disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase, which catalyzes a step in the catabolism of glycosaminoglycans. In patients with mucopolysaccharidosis II, glycosaminoglycans accumulate within tissues and organs, contributing to the signs and symptoms of the disease. Mucopolysaccharidosis II affects multiple organs and physiologic systems and has a variable age of onset and variable rate of progression. Common presenting features include excess urinary glycosaminoglycan excretion, facial dysmorphism, organomegaly, joint stiffness and contractures, pulmonary dysfunction, myocardial enlargement and valvular dysfunction, and neurologic involvement. In patients with neurologic involvement, intelligence is impaired, and death usually occurs in the second decade of life, whereas those patients with minimal or no neurologic involvement may survive into adulthood with normal intellectual development. Enzyme replacement therapy has emerged as a new treatment for mucopolysaccharidosis disorders, including Hunter syndrome. The purpose of this report is to provide a concise review of mucopolysaccharidosis II for practitioners with the hope that such information will help identify affected boys earlier in the course of their disease.

The mucopolysaccharidoses: a success of molecular medicine

The mucopolysaccharidoses represent a devastating group of lysosomal storage diseases affecting approximately 1 in 25 000 individuals. Advances in biochemistry and genetics over the past 25 years have resulted in the identification of the key hydrolases underlying the mucopolysaccharidoses, with subsequent isolation and characterisation of the genes involved. Ultimately these advances have led to the recent development of specific treatment regimens for some of the mucopolysaccharidoses, in the form of direct enzyme replacement. Direct replacement of the defective gene product has been attempted for very few genetic disorders, and thus the experience gained in the lysosomal storage diseases by the development, evaluation and integration of treatment regimens into healthcare is instructive for other rare genetic disorders. This review focuses on the pathophysiology of the mucopolysaccharidoses and highlights the complex biochemical and physiological perturbations that underlie the disease phenotype.

Preclinical dose ranging studies for enzyme replacement therapy with idursulfase in a knock-out mouse model of MPS II

Mucopolysaccharidosis II (MPS II; Hunter syndrome) is an X-linked metabolic disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase (I2S), which catalyzes the catabolism of glycosaminoglycans (GAG) by cleaving the O-linked sulfate from dermatan sulfate and heparan sulfate. Recently, enzyme replacement therapy (ERT) with recombinant human I2S (Elaprase (idursulfase), Shire Human Genetic Therapies, Inc.), has been approved in the US and European Union for the treatment and management of MPS II. The purpose of the studies presented here was to describe some of the preclinical development of idursulfase using the I2S knock-out mouse model of MPS II designed to study the effect of dose and various dosing regimens of idursulfase on urine and tissue GAG levels. Urine and tissue samples were collected prior to idursulfase treatment and periodically throughout each study and analyzed for GAGs. The presence of anti-idursulfase antibodies in the mice serum after idursulfase use was also determined. Results showed that idursulfase, at several doses and at several dosing frequencies, caused a reduction in tissue and urine GAG levels in a dose-dependent manner. These studies also demonstrated that after IV administration, idursulfase is biologically active in the IdS-KO mouse model and is transported to key target tissues, reaching the lysosomes in an active form, and degrading the accumulated GAG. In conclusion, these results indicated that ERT with idursulfase produced in a human cell line could be useful in the treatment and management of MPS II, and were used in the design of clinical studies to evaluate the efficacy of idursulfase in MPS II patients.

Mucopolysaccharidosis type II: an update on mutation spectrum

Mucopolysaccharidosis type II (MPS II; Hunter disease) is caused by deficiency of the enzyme iduronate-2-sulphatase (IDS) and patients present with a wide range of clinical signs and symptoms. The level of activity of IDS, however, does not allow prediction of phenotype. In our study of unrelated individuals with MPS II, alterations in the IDS gene could be identified in all 155 patients. Investigations in families in which the occurrence of MPS II was sporadic revealed mosaicism in the mothers of a small number of patients and a high frequency of de novo mutations occurring preferentially during male meiosis. Mutations identified in our patients include 27 large alterations and 128 small gene alterations (96 different alterations). These data further confirm the extreme heterogeneity of IDS gene alterations, as more than 330 have been reported to date. This genetic heterogeneity may explain the high degree of clinical heterogeneity in MPS II. Therefore, attempts have been made to establish genotype-phenotype correlations in order to provide an indication of the likely prognosis and a basis on which to evaluate treatment. To date, some progress has been made in predicting the clinical phenotype from the genotype although it remains difficult in a few individual cases. However, as the crystallographic 3D structure of IDS is yet to be determined, evaluation of the impact of mutations on IDS activity is often time consuming. Furthermore, if a given mutation is recurrent, some patients carrying the same change may present with different phenotypes, suggesting that factors other than the IDS gene (e.g. other genes, environmental factors) can modulate the clinical phenotype.

CONCLUSION

Although genotype-phenotype correlations may be difficult to establish, they will be of increasing importance for choosing the most appropriate therapy for an individual patient, as new therapeutic strategies may be targeted according to phenotype.

Idursulfase: enzyme replacement therapy for mucopolysaccharidosis Type II (Hunter syndrome)

Mucopolysaccharidosis type II (Hunter syndrome) is a lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase leading to tissue accumulation of glycosaminoglycans. It manifests with short stature, joint stiffness, coarse facial features, hepatosplenomegaly, and progressive mental retardation. Most children die in the first or second decade from pulmonary or cardiac involvement. Until recently, no specific treatment was available. A Phase II/III trial of idursulfase, a recombinant enzyme replacement therapy for this disorder, demonstrated significant improvement in a 6-min walk test and in pulmonary function tests, and a decrease in liver and spleen size among those receiving active therapy once weekly. Major side effects include allergic reactions, which generally are easily managed and do not require discontinuing therapy. Idursulfase is now approved in the US, and should provide significant improvement in quality of life for these individuals. This article reviews the disease and treatment, with comments on future therapeutic directions.

Effect of Hunter disease (mucopolysaccharidosis type II) mutations on molecular phenotypes of iduronate-2-sulfatase: enzymatic activity, protein processing and structural analysis

Mucopolysaccharidosis II (Hunter disease), a lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase (IDS), has variable clinical phenotypes. Nearly 300 different mutations have been identified in the IDS gene from patients with Hunter disease, but the correlation between the genotype and phenotype has remained unclear. We studied the characteristics of 11 missense mutations, which were detected in the patients or artificially introduced, using stable expression experiments and structural analysis. The mutants found in the attenuated phenotype showed considerable residual activity (0.2-2.4% of the wild-type IDS activity) and those in the severe phenotype had no activity. In immunoblot analysis, both the 73-75 kDa precursor and processed forms were detected in the expression of 'attenuated' mutants (R48P, A85T and W337R) and the artificial active site mutants (C84S, C84T). The 73-75 kDa initial precursor was detected in the 'severe' mutants (P86L, S333L, S349I, R468Q, R468L). The truncated 68 kDa precursor form was synthesized in the Q531X mutant. The results of immunoblotting indicated rapid degradation and/or insufficiency in processing as a result of structural alteration of the IDS protein. A combination of analyses of genotype and molecular phenotypes, including enzyme activity, protein processing and structural analysis with an engineered reference protein, could provide an avenue to understanding the molecular mechanism of the disease and could give a useful tool for the evaluation of possible therapeutic chemical compounds.

A phase II/III clinical study of enzyme replacement therapy with idursulfase in mucopolysaccharidosis II (Hunter syndrome)

PURPOSE

To evaluate the safety and efficacy of recombinant human iduronate-2-sulfatase (idursulfase) in the treatment of mucopolysaccharidosis II.

METHODS

Ninety-six mucopolysaccharidosis II patients between 5 and 31 years of age were enrolled in a double-blind, placebo-controlled trial. Patients were randomized to placebo infusions, weekly idursulfase (0.5 mg/kg) infusions or every-other-week infusions of idursulfase (0.5 mg/kg). Efficacy was evaluated using a composite endpoint consisting of distance walked in 6 minutes and the percentage of predicted forced vital capacity based on the sum of the ranks of change from baseline.

RESULTS

Patients in the weekly and every-other-week idursulfase groups exhibited significant improvement in the composite endpoint compared to placebo (P = 0.0049 for weekly and P = 0.0416 for every-other-week) after one year. The weekly dosing group experienced a 37-m increase in the 6-minute-walk distance (P = 0.013), a 2.7% increase in percentage of predicted forced vital capacity (P = 0.065), and a 160 mL increase in absolute forced vital capacity (P = 0.001) compared to placebo group at 53 weeks. Idursulfase was generally well tolerated, but infusion reactions did occur. Idursulfase antibodies were detected in 46.9% of patients during the study.

CONCLUSION

This study supports the use of weekly infusions of idursulfase in the treatment of mucopolysaccharidosis II.

Differences in methylation patterns in the methylation boundary region of IDS gene in Hunter syndrome patients: implications for CpG hot spot mutations

Hunter syndrome, an X-linked disorder, results from deficiency of iduronate-2-sulfatase (IDS). Around 40% of independent point mutations at IDS were found at CpG sites as transitional events. The 15 CpG sites in the coding sequences of exons 1 and 2, which are normally hypomethylated, account for very few of transitional mutations. By contrast, the CpG sites in the coding sequences of exon 3, though also normally hypomethylated, account for much higher fraction of transitional mutations. To better understand relationship between methylation status and CpG transitional mutations in this region, the methylation patterns of 11 Hunter patients with transitional mutations at CpG sites were investigated using bisulfite genomic sequencing. The patient cohort mutation spectrum is composed of one mutation in exon 1 (one patient) and three different mutations in exon 3 (10 patients). We confirmed that in normal males, cytosines at the CpG sites from the promoter region to a portion of intron 3 were hypomethylated. However, specific CpG sites in this area were more highly methylated in patients. The patients with p.R8X (exon 1), p.P86L (exon 3), and p.R88H (exon 3) mutations had a hypermethylated condition in exon 2 to intron 3 but retained hypomethylation in exon 1. The same trend was found in four patients with p.A85T (exon 3), although the degree of hypermethylation was less. These findings suggest methylation patterns in the beginning of IDS genomic region are polymorphic in humans and that hypermethylation in this region in some individuals predisposes them to CpG mutations resulting in Hunter syndrome.