Study of Intraventricular Cerliponase Alfa for CLN2 Disease

MRI in CLN2 disease patients: Subtle features that support an early diagnosis

Neuronal ceroid lipofuscinosis type 2 (CLN2) disease is a rare, paediatric-onset, neurodegenerative disorder characterised in its early stages by language delay, seizures and loss of motor function. It is rapidly progressive and ultimately results in the premature death of patients. We aim to highlight common magnetic resonance imaging (MRI) features seen in early CLN2 disease and increase disease awareness among clinicians in order to facilitate early diagnosis and treatment of patients with disease-modifying enzyme replacement therapy. We obtained MRI scans from 12 Turkish children with CLN2 disease, at symptom onset or time of diagnosis, and at various times during disease progression. Patient details including age at onset of symptoms, age at diagnosis and clinical presentation were collected. MRIs were analysed to identify common features present in patients with CLN2 disease. The median diagnostic delay in this cohort was 2 years, highlighting the need for increased disease awareness among clinicians. Key MRI features suggestive of CLN2 disease that were identified included cerebellar atrophy in 11 patients, linear hyperintensity of central white matter in 10 patients, cerebral atrophy in 8 patients and thinning of the corpus callosum in 6 patients. Thalamic hypointensity was seen in 1 patient and may also indicate CLN2 disease. It is important to consider the presenting symptoms alongside clinical test results in order to support early diagnosis of CLN2 disease. Clinical suspicion of CLN2 disease accompanied by the detection of any of the above-mentioned features on MRI should encourage healthcare professionals to test for CLN2 disease.

An iPSC-Derived Neuron Model of CLN3 Disease Facilitates Small Molecule Phenotypic Screening

The neuronal ceroid lipofuscinoses (NCLs) are a family of rare lysosomal storage disorders. The most common form of NCL occurs in children harboring a mutation in the CLN3 gene. This form is lethal with no existing cure or treatment beyond symptomatic relief. The pathophysiology of CLN3 disease is complex and poorly understood, with current in vivo and in vitro models failing to identify pharmacological targets for therapeutic intervention. This study reports the characterization of the first CLN3 patient-specific induced pluripotent stem cell (iPSC)-derived model of the blood-brain barrier and establishes the suitability of an iPSC-derived neuron model of the disease to facilitate compound screening. Upon differentiation, hallmarks of CLN3 disease are apparent, including lipofuscin and subunit c of mitochondrial ATP synthase accumulation, mitochondrial dysfunction, and attenuated Bcl-2 expression. The model led to the identification of small molecules that cleared subunit c accumulation by mTOR-independent modulation of autophagy, conferred protective effects through induction of Bcl-2 and rescued mitochondrial dysfunction.

Intracerebroventricular Cerliponase Alfa for Neuronal Ceroid Lipofuscinosis Type 2 Disease: Clinical Practice Considerations From US Clinics

BACKGROUND

Neuronal ceroid lipofuscinosis type 2 or CLN2 disease is a rare, autosomal recessive, neurodegenerative lysosomal storage disorder caused by tripeptidyl peptidase 1 deficiency. Cerliponase alfa, a recombinant human tripeptidyl peptidase 1 enzyme, is the first and only approved treatment for CLN2 disease and the first approved enzyme replacement therapy administered via intracerebroventricular infusion.

METHODS

A meeting of health care professionals from US institutions with experience in cerliponase alfa treatment of children with CLN2 disease was held in November 2018. Key common practices were identified, and later refined during the drafting of this article, that facilitate safe chronic administration of cerliponase alfa.

RESULTS

Key practices include developing a multidisciplinary team of clinicians, pharmacists, and coordinators, and institution-specific processes. Infection risk may be reduced through strict aseptic techniques and minimizing connections and disconnections during infusion. The impact of intracerebroventricular device design on port needle stability during extended intracerebroventricular infusion is a critical consideration in device selection. Monitoring for central nervous system infection is performed at each patient contact, but with flexibility in the degree of monitoring. Although few institutions had experienced positive cerebrospinal fluid test results, the response to a positive cerebrospinal fluid culture should be determined on a case-by-case basis, and the intracerebroventricular device should be removed if cerebrospinal fluid infection is confirmed.

CONCLUSIONS

The key common practices and flexible practices used by institutions with cerliponase alfa experience may assist other institutions in process development. Continued sharing of experiences will be essential for developing standards and patient care guidelines.

GM2 Gangliosidoses: Clinical Features, Pathophysiological Aspects, and Current Therapies

GM2 gangliosidoses are a group of pathologies characterized by GM2 ganglioside accumulation into the lysosome due to mutations on the genes encoding for the β-hexosaminidases subunits or the GM2 activator protein. Three GM2 gangliosidoses have been described: Tay-Sachs disease, Sandhoff disease, and the AB variant. Central nervous system dysfunction is the main characteristic of GM2 gangliosidoses patients that include neurodevelopment alterations, neuroinflammation, and neuronal apoptosis. Currently, there is not approved therapy for GM2 gangliosidoses, but different therapeutic strategies have been studied including hematopoietic stem cell transplantation, enzyme replacement therapy, substrate reduction therapy, pharmacological chaperones, and gene therapy. The blood-brain barrier represents a challenge for the development of therapeutic agents for these disorders. In this sense, alternative routes of administration (e.g., intrathecal or intracerebroventricular) have been evaluated, as well as the design of fusion peptides that allow the protein transport from the brain capillaries to the central nervous system. In this review, we outline the current knowledge about clinical and physiopathological findings of GM2 gangliosidoses, as well as the ongoing proposals to overcome some limitations of the traditional alternatives by using novel strategies such as molecular Trojan horses or advanced tools of genome editing.

Neuronal ceroid lipofuscinosis type 2: an Australian case series

AIM

Late infantile neuronal ceroid lipofuscinosis type 2 (CLN2) disease is a rare neurodegenerative disorder presenting in children aged 2-4 years with seizures and loss of motor and language skills, followed by blindness and death in late childhood. Initial presenting features are similar to a range of common epilepsies. We aim to highlight typical clinical and radiological features that may prompt diagnosis of CLN2 disease in early disease stages.

METHODS

We present a series of 13 Australian patients with CLN2 disease, describing clinical features, disease evolution, neuroimaging, electroencephalogram, biochemical and genetic results. Expert neuroradiological magnetic resonance imaging (MRI) analysis was retrospectively performed on 10 cases.

RESULTS

Twelve patients presented with seizures, with initial seizures being focal (n = 4), generalised tonic-clonic (n = 3), absence (n = 3) and febrile (n = 2). Eleven patients (85%) had a language delay before the onset of seizures. Cerebellar or cerebral atrophy was noted in all patients on centralised MRI review, with abnormalities of the brain-stem, ventricles, corpus callosum and hippocampi.

CONCLUSIONS

Early language delay with the onset of seizures at 2-4 years of age is the hallmark of CLN2 disease. MRI findings of early subtle atrophy in the cerebellum or posterior cortical regions should hasten testing for CLN2 disease to enable early initiation of enzyme replacement therapy.

Inherited Metabolic Disorders Presenting with Ataxia

Ataxia is a common clinical feature in inherited metabolic disorders. There are more than 150 inherited metabolic disorders in patients presenting with ataxia in addition to global developmental delay, encephalopathy episodes, a history of developmental regression, coarse facial features, seizures, and other types of movement disorders. Seizures and a history of developmental regression especially are important clinical denominators to consider an underlying inherited metabolic disorder in a patient with ataxia. Some of the inherited metabolic disorders have disease specific treatments to improve outcomes or prevent early death. Early diagnosis and treatment affect positive neurodevelopmental outcomes, so it is important to think of inherited metabolic disorders in the differential diagnosis of ataxia.

Targeted re-sequencing for early diagnosis of genetic causes of childhood epilepsy: the Italian experience from the 'beyond epilepsy' project

Background

Childhood epilepsies are a heterogeneous group of conditions differing in diagnostic criteria, management, and outcome. Late-infantile neuronal ceroid lipofuscinosis type 2 (CLN2) is a neurodegenerative condition caused by biallelic TPP1 variants. This disorder presents with subtle and relatively non-specific symptoms, mimicking those observed in more common paediatric epilepsies and followed by rapid psychomotor deterioration and drug-resistant epilepsy. A prompt diagnosis is essential to adopt appropriate treatment and disease management strategies.

Methods

This is a prospective, multicentre study on the efficiency of targeted re-sequencing in the early identification of the genetic causes of childhood epilepsy, with particular regard to CLN2. After phenotypic characterization, a 283-gene Next Generation Sequencing panel was performed in 21 Italian children with neurodevelopmental abnormalities, aged between 24 and 60 months, experiencing first unprovoked seizure after 2 years of age.

Results

The average age at enrolment was 39.9 months, with a mean age at seizure onset of 30.9 months and a mean time interval between seizure onset and targeted resequencing of 9 months. Genetic confirmation was achieved in 4 out of 21 patients, with a diagnostic yield of 19%. In one case, the homozygous splice acceptor variant c.509-1G > C in TPP1 was identified, leading to a CLN2 diagnosis. Three pathogenic variants in MECP2 were also detected in three patients, including the frameshift variant c.1157_1186delinsA (p.Leu386Hisfs*9) in a girl with negative single gene sequencing. Variants of unknown significance (VUS) were found in 11 out of 21 (52.4%) individuals, whereas no clinically significant variants were observed in the remaining 6 subjects.

Conclusions

Our findings support the efficacy of target re-sequencing in the identification of the genetic causes of childhood epilepsy and suggest that this technique might prove successful in the early detection of CLN2 as well as other neurodevelopmental conditions.

Intravitreal enzyme replacement inhibits progression of retinal degeneration in canine CLN2 neuronal ceroid lipofuscinosis

CLN2 neuronal ceroid lipofuscinosis is a rare recessive hereditary retinal and neurodegenerative disease resulting from deleterious sequence variants in TPP1 that encodes the soluble lysosomal enzyme tripeptidyl peptidase-1 (TPP1). Children with this disorder develop normally, but starting at 2-4 years of age begin to exhibit neurological signs and visual deficits. Vision loss that progresses to blindness is associated with progressive retinal degeneration and impairment of retinal function. Similar progressive loss of retinal function and retinal degeneration occur in a dog CLN2 disease model with a TPP1 null sequence variant. Studies using the dog model were conducted to determine whether intravitreal injection of recombinant human TPP1 (rhTPP1) administered starting after onset of retinal functional impairment could slow or halt the progression of retinal functional decline and degeneration. TPP1-null dogs received intravitreal injections of rhTPP1 in one eye and vehicle in the other eye beginning at 23.5-25 weeks of age followed by second injections at 34-40 weeks in 3 out of 4 dogs. Ophthalmic exams, in vivo ocular imaging, and electroretinography (ERG) were repeated regularly to monitor retinal structure and function. Retinal histology was evaluated in eyes collected from these dogs when they were euthanized at end-stage neurological disease (40-45 weeks of age). Intravitreal rhTPP1 injections were effective in preserving retinal function (as measured with the electroretinogram) and retinal morphology for as long as 4 months after a single treatment. These findings indicate that intravitreal injection of rhTPP1 administered after partial loss of retinal function is an effective treatment for preserving retinal structure and function in canine CLN2 disease.

Gene Therapy Targeting the Inner Retina Rescues the Retinal Phenotype in a Mouse Model of CLN3 Batten Disease

The neuronal ceroid lipofuscinoses (NCLs), often referred to as Batten disease, are inherited lysosomal storage disorders that represent the most common neurodegeneration during childhood. Symptoms include seizures, vision loss, motor and cognitive decline, and premature death. The development of brain-directed treatments for NCLs has made noteworthy progress in recent years. Clinical trials are currently ongoing or planned for different forms of the disease. Despite these promising advances, it is unlikely that therapeutic interventions targeting the brain will prevent loss of vision in patients as retinal cells remain untreated and will continue to degenerate. Here, we demonstrate that Cln3^Δex7/8 mice, a mouse model of CLN3 Batten disease with juvenile onset, suffer from a decline in inner retinal function resulting from the death of rod bipolar cells, interneurons vital for signal transmission from photoreceptors to ganglion cells in the retina. We also show that this ocular phenotype can be treated by adeno-associated virus (AAV)-mediated expression of CLN3 in cells of the inner retina, leading to significant survival of bipolar cells and preserved retinal function. In contrast, the treatment of photoreceptors, which are lost in patients at late disease stages, was not therapeutic in Cln3^Δex7/8 mice, underlining the notion that CLN3 disease is primarily a disease of the inner retina with secondary changes in the outer retina. These data indicate that bipolar cells play a central role in this disease and identify this cell type as an important target for ocular AAV-based gene therapies for CLN3 disease.

Intravitreal enzyme replacement preserves retinal structure and function in canine CLN2 neuronal ceroid lipofuscinosis

CLN2 neuronal ceroid lipofuscinosis is a hereditary neurodegenerative disorder characterized by progressive vision loss, neurological decline, and seizures. CLN2 disease results from mutations in TPP1 that encodes the lysosomal enzyme tripeptidyl peptidase-1 (TPP1). Children with CLN2 neuronal ceroid lipofuscinosis experience ocular disease, characterized by progressive retinal degeneration associated with impaired retinal function and gradual vision loss culminating in total blindness. A similar progressive loss of retinal function is also observed in a dog CLN2 model with a TPP1 null mutation. A study was conducted to evaluate the efficacy of periodic intravitreal injections of recombinant human (rh) TPP1 in inhibiting retinal degeneration and preserving retinal function in the canine model. TPP1 null dogs received periodic intravitreal injections of rhTPP1 in one eye and vehicle in the other eye beginning at approximately 12 weeks of age. Ophthalmic exams, in vivo ocular imaging, and electroretinography (ERG) were repeated regularly to monitor retinal structure and function. Retinal histology was evaluated in eyes collected from these dogs when they were euthanized at end-stage neurological disease (43-46 weeks of age). Intravitreal rhTPP1 dosing prevented disease-related declines in ERG amplitudes in the TPP1-treated eyes. At end-stage neurologic disease, TPP1-treated eyes retained normal morphology while the contralateral vehicle-treated eyes exhibited loss of inner retinal neurons and photoreceptor disorganization typical of CLN2 disease. The treatment also prevented the development of disease-related focal retinal detachments observed in the control eyes. Uveitis occurred secondary to the administration of the rhTPP1 but did not hinder the therapeutic benefits. These findings demonstrate that periodic intravitreal injection of rhTPP1 preserves retinal structure and function in canine CLN2 disease.

Enzyme therapy: a forerunner in catalyzing a healthy society?

INTRODUCTION

The use of enzymes in various industries has been prevalent for centuries. However, their potency as therapeutics remained latent until the late 1950 s, when scientists finally realized the gold mine they were sitting on. Enzyme therapy has seen rapid development over the past few decades and has been widely used for the therapy of myriad diseases, including lysosomal storage disorders, cancer, Alzheimer's disease, irritable bowel syndrome, exocrine pancreatic insufficiency, and hyperuricemia. Enzymes are also used for wound healing, the treatment of microbial infections, and gene therapy.

AREAS COVERED

This is a comprehensive review of the therapeutic use of enzymes that can act as a guidepost for researchers and academicians and presents a general overview of the developments in enzyme therapy over the years, along with updates on recent advancements in enzyme therapy research.

EXPERT OPINION

Although enzyme therapy is immensely beneficial and induces little auxiliary damage, it has several drawbacks, ranging from high cost, low stability, low production, and hyperimmune responses to the failure to cure a variety of the problems associated with a disease. Further fine-tuning and additional clinical efficacy studies are required to establish enzyme therapy as a forerunner to catalyzing a healthy society.

MRI characterization of early CNS transport kinetics post intrathecal gadolinium injection: Trends of subarachnoid and parenchymal distribution in healthy volunteers

PURPOSE

To quantify CSF transport kinetics and brain glymphatic distribution using MRI following intrathecal injection of gadolinium contrast in healthy adults.

SUBJECTS AND METHODS

Eight completely healthy volunteer subjects underwent intrathecal injection of gadolinium via image guided lumbar puncture and serial MRI's at six subsequent time points up to 11 h post-injection. Rate of enhancement and deposition were calculated for various regions and lobes of the brain.

RESULTS

Normalized cranial data revealed that gadolinium in the intracranial CSF spaces peaked within 1-3 h and started to decrease at 7 h. In some regions of the brain parenchyma, such as the cerebral cortex and white matter, enhancement was increasing after 11 h. Differential rates of uptake between the parietal and frontal (p = 0.0003), cingulate (p = 0.002) and temporal (p = 0.018) lobes were shown as well as a several fold change between various cortical regions. Lastly, a linear regression comparing laterality between 35 cortical regions yielded (R² = 0.90, p < 0.001) with a slope of 1.01 showing symmetry in uptake.

CONCLUSIONS

Gadolinium enhancement after lumbar intrathecal injection demonstrated differential CSF flow and brain parenchymal penetration, which illustrated the distributory function of the glymphatic system.

Global Brain Transcriptome Analysis of a Tpp1 Neuronal Ceroid Lipofuscinoses Mouse Model

In humans, homozygous mutations in the TPP1 gene results in loss of tripeptidyl peptidase 1 (TPP1) enzymatic activity, leading to late infantile neuronal ceroid lipofuscinoses disease. Using a mouse model that targets the Tpp1 gene and recapitulates the pathology and clinical features of the human disease, we analyzed end-stage (4 months) transcriptional changes associated with lack of TPP1 activity. Using RNA sequencing technology, Tpp1 expression changes in the forebrain/midbrain and cerebellum of 4-month-old homozygotes were compared with strain-related controls. Transcriptional changes were found in 510 and 1,550 gene transcripts in forebrain/midbrain and cerebellum, respectively, from Tpp1-deficient brain tissues when compared with age-matched controls. Analysis of the differentially expressed genes using the Ingenuity™ pathway software, revealed increased neuroinflammation activity in microglia and astrocytes that could lead to neuronal dysfunction, particularly in the cerebellum. We also observed upregulation in the production of nitric oxide and reactive oxygen species; activation of leukocyte extravasation signals and complement pathways; and downregulation of major transcription factors involved in control of circadian rhythm. Several of these expression changes were confirmed by independent quantitative polymerase chain reaction and histological analysis by mRNA in situ hybridization, which allowed for an in-depth anatomical analysis of the pathology and provided independent confirmation of at least two of the major networks affected in this model. The identification of differentially expressed genes has revealed new lines of investigation for this complex disorder that may lead to novel therapeutic targets.

Diagnosis of late-infantile neuronal ceroid lipofuscinosis using dried blood spot-based assay for TPPI enzyme activity: TPPI diagnostic assay from DBS

BACKGROUND

The neuronal ceroid lipofuscinosis 2 (NCL2) or classic late-infantile neuronal ceroid lipofuscinosis (LINCL) is a neurogenetic disorder caused by mutations in the TPPI gene, which codes for the lysosomal tripeptidyl peptidase 1 (TPPI) EC 3.4.14.9. Loss of functional TPPI activity results in progressive visual and neurological symptoms starting at around 1-2 years of age causing early death.

METHODS

We report a DBS-based TPPI assay that cleaves a synthetic tetrapeptide substrate generating a product that is detected by HPLC. Probands and carriers were identified with 100% accuracy (7 probands, 30 carriers, 13 controls).

RESULTS

The assay detected a single TPPI activity at a lower pH towards the substrate tested. TPPI activity measurable when extracted at lower pH while inactive at neutral pH showed steady increase for at least 8 h incubation. No loss in TPPI activity was observed when DBS were stored for at least 2 weeks either in freezer, refrigerator, room temperature or 42 °C.

CONCLUSION

A sequence variant causing Arg339Gln substitution in a proband had 12% TPPI. TPPI activity can be reliably measured in DBS, giving an opportunity to diagnose NCL2 at birth and refer patients for enzyme replacement or other therapies for earliest intervention, or alternatively offers a second-tier confirmatory test.

FDA orphan drug designations for lysosomal storage disorders - a cross-sectional analysis

Purpose

To provide a quantitative clinical-regulatory insight into the status of FDA orphan drug designations for compounds intended to treat lysosomal storage disorders (LSDs).

Methods

Assessment of the drug pipeline through analysis of the FDA database for orphan drug designations with descriptive and comparative statistics.

Results

Between 1983 and 2019, 124 orphan drug designations were granted by the FDA for compounds intended to treat 28 lysosomal storage diseases. Orphan drug designations focused on Gaucher disease (N = 16), Pompe disease (N = 16), Fabry disease (N = 10), MPS II (N = 10), MPS I (N = 9), and MPS IIIA (N = 9), and included enzyme replacement therapies, gene therapies, and small molecules, and others. Twenty-three orphan drugs were approved for the treatment of 11 LSDs. Gaucher disease (N = 6), cystinosis (N = 5), Pompe disease (N = 3), and Fabry disease (N = 2) had multiple approvals, CLN2, LAL-D, MPS I, II, IVA, VI, and VII one approval each. This is an increase of nine more approved drugs and four more treatable LSDs (CLN2, MPS VII, LAL-D, and MPS IVA) since 2013. Mean time between orphan drug designation and FDA approval was 89.7 SD 55.00 (range 8–203, N = 23) months.

Conclusions

The drug development pipeline for LSDs is growing and evolving, with increased focus on diverse small-molecule targets and gene therapy. CLN2 was the first and only LSD with an approved therapy directly targeted to the brain. Newly approved products included “me-too”–enzymes and innovative compounds such as the first pharmacological chaperone for the treatment of Fabry disease.

Review of Cerliponase Alfa: Recombinant Human Enzyme Replacement Therapy for Late-Infantile Neuronal Ceroid Lipofuscinosis Type 2

The objective of this review is to summarize the pharmacology, efficacy, and safety of cerliponase alfa for the treatment of late infantile neuronal ceroid lipofuscinosis type 2 (CLN2). Cerliponase alfa is recombinant human tripeptidyl peptidase 1 enzyme replacement therapy. A phase 1/2 trial established the efficacy and safety of cerliponase alfa for treatment of neuronal ceroid lipofuscinosis type 2. Treatment with intracerebroventricular cerliponase alfa resulted in slower decline of motor and language functions compared with natural history controls. Common adverse events include convulsions, electrocardiography abnormalities, pyrexia, vomiting, and upper respiratory tract infections. Intracerebroventricular device-related adverse events also occur. Cerliponase alfa is the first therapy for neuronal ceroid lipofuscinosis type 2 that targets the disease etiology. Cerliponase alfa is effective in delaying the progression of motor language decline for patients with neuronal ceroid lipofuscinosis type 2.

Changing Times for CLN2 Disease: The Era of Enzyme Replacement Therapy

Neuronal ceroid lipofuscinosis type 2 (CLN2 disease) is a progressive neurodegenerative disease that results in early-onset, severe, progressive, neurological disabilities, leading to death in late childhood or early adolescence. Management has relied on symptomatic care, and supportive and palliative strategies, but the approval of the enzyme replacement therapy cerliponase alfa in the USA and Europe in 2017 brought different treatment opportunities. We describe the natural history of CLN2 disease, its diagnosis and management, and the preclinical and clinical development of cerliponase alfa. A PubMed search was undertaken for cerliponase alfa and rhTPP1 to identify preclinical and clinical studies. The hallmark-presenting symptoms of CLN2 disease are unprovoked seizures and a history of language delay, and progression involves motor dysfunction, and cognitive and visual decline. Cerliponase alfa has shown efficacy and tolerability in mouse and canine models of CLN2 disease when delivered intracerebroventricularly. Administration of cerliponase alfa in patients with CLN2 disease has led to significant reductions in the rate of decline of motor and language functions in comparison with a natural history population. The approval of cerliponase alfa has brought a new era for CLN2 disease, highlighting the need to understand different patterns of disease progression and clinical needs in treated patients.

Proteomic and functional analyses in disease models reveal CLN5 protein involvement in mitochondrial dysfunction

CLN5 disease is a rare form of late-infantile neuronal ceroid lipofuscinosis (NCL) caused by mutations in the CLN5 gene that encodes a protein whose primary function and physiological roles remains unresolved. Emerging lines of evidence point to mitochondrial dysfunction in the onset and progression of several forms of NCL, offering new insights into putative biomarkers and shared biological processes. In this work, we employed cellular and murine models of the disease, in an effort to clarify disease pathways associated with CLN5 depletion. A mitochondria-focused quantitative proteomics approach followed by functional validations using cell biology and immunofluorescence assays revealed an impairment of mitochondrial functions in different CLN5 KO cell models and in Cln5 - /- cerebral cortex, which well correlated with disease progression. A visible impairment of autophagy machinery coupled with alterations of key parameters of mitophagy activation process functionally linked CLN5 protein to the process of neuronal injury. The functional link between impaired cellular respiration and activation of mitophagy pathways in the human CLN5 disease condition was corroborated by translating organelle-specific proteome findings to CLN5 patients' fibroblasts. Our study highlights the involvement of CLN5 in activation of mitophagy and mitochondrial homeostasis offering new insights into alternative strategies towards the CLN5 disease treatment.

Emerging treatments for progressive myoclonus epilepsies

Introduction: Progressive myoclonus epilepsies (PMEs) are a group of neurodegenerative diseases, invariably leading to severe disability or fatal outcome in a few years or decades. Nowadays, PMEs treatment remains challenging with a significant burden of disability for patients. Pharmacotherapy is primarily used to treat seizures, which impact patients' quality of life. However, new approaches have emerged in the last few years, which try to curb the neurological deterioration of PMEs through a better knowledge of the pathogenetic process. This is a review on the newest therapeutic options for the treatment of PMEs.Areas covered: Experimental and clinical results on novel therapeutic approaches for the different forms of PME are reviewed and discussed. Special attention is primarily focused on the efficacy and tolerability outcomes, trying to infer the role novel approaches may have in the future.Expert opinion: The large heterogeneity of disease-causing mechanisms prevents researchers from identifying a single approach to treat PMEs. Understanding of pathophysiologic processes is leading the way to targeted therapies, which, through enzyme replacement or underlying gene defect correction have already proved to potentially strike on neurodegeneration.

Succinic Semialdehyde Dehydrogenase Deficiency: An Update

Succinic semialdehyde dehydrogenase deficiency (SSADH-D) is a genetic disorder that results from the aberrant metabolism of the neurotransmitter γ-amino butyric acid (GABA). The disease is caused by impaired activity of the mitochondrial enzyme succinic semialdehyde dehydrogenase. SSADH-D manifests as varying degrees of mental retardation, autism, ataxia, and epileptic seizures, but the clinical picture is highly heterogeneous. So far, there is no approved curative therapy for this disease. In this review, we briefly summarize the molecular genetics of SSADH-D, the past and ongoing clinical trials, and the emerging features of the molecular pathogenesis, including redox imbalance and mitochondrial dysfunction. The main aim of this review is to discuss the potential of further therapy approaches that have so far not been tested in SSADH-D, such as pharmacological chaperones, read-through drugs, and gene therapy. Special attention will also be paid to elucidating the role of patient advocacy organizations in facilitating research and in the communication between researchers and patients.

A Scoping Review of Inborn Errors of Metabolism Causing Progressive Intellectual and Neurologic Deterioration (PIND)

Background: Progressive intellectual and neurological deterioration (PIND) is a rare but severe childhood disorder characterized by loss of intellectual or developmental abilities, and requires quick diagnosis to ensure timely treatment to prevent possible irreversible neurological damage. Inborn errors of metabolism (IEMs) constitute a group of more than 1,000 monogenic conditions in which the impairment of a biochemical pathway is intrinsic to the pathophysiology of the disease, resulting in either accumulation of toxic metabolites and/or shortage of energy and building blocks for the cells. Many IEMs are amenable to treatment with the potential to improve outcomes. With this literature review we aim to create an overview of IEMs presenting with PIND in children, to aid clinicians in accelerating the diagnostic process. Methods: We performed a PubMed search on IEMs presenting with PIND in individuals aged 0-18 years. We applied stringent selection criteria and subsequently derived information on encoding genes, pathways, clinical and biochemical signs and diagnostic tests from IEMbase (www.iembase.org) and other sources. Results: The PubMed search resulted in a total of 2,152 articles and a review of references added another 19 articles. After applying our selection criteria, a total of 85 IEMs presenting with PIND remained, of which 57 IEMs were reported in multiple unrelated cases and 28 in single families. For 44 IEMs (52%) diagnosis can be achieved through generally accessible metabolic blood and urine screening tests; the remainder requires enzymatic and/or genetic testing. Treatment targeting the underlying pathophysiology is available for 35 IEMs (41%). All treatment strategies are reported to achieve stabilization of deterioration, and a subset improved seizure control and/or neurodevelopment. Conclusions: We present the first comprehensive overview of IEMs presenting with PIND, and provide a structured approach to diagnosis and overview of treatability. Clearly IEMs constitute the largest group of genetic PIND conditions and have the advantage of detectable biomarkers as well as amenability to treatment. Thus, the clinician should keep IEMs at the forefront of the diagnostic workup of a child with PIND. With the ongoing discovery of new IEMs, expanded phenotypes, and novel treatment strategies, continuous updates to this work will be required.

Lysosomal protein thermal stability does not correlate with cellular half-life: global observations and a case study of tripeptidyl-peptidase 1

Late-infantile neuronal ceroid lipofuscinosis (LINCL) is a neurodegenerative lysosomal storage disorder caused by mutations in the gene encoding the protease tripeptidyl-peptidase 1 (TPP1). Progression of LINCL can be slowed or halted by enzyme replacement therapy, where recombinant human TPP1 is administered to patients. In this study, we utilized protein engineering techniques to increase the stability of recombinant TPP1 with the rationale that this may lengthen its lysosomal half-life, potentially increasing the potency of the therapeutic protein. Utilizing multiple structure-based methods that have been shown to increase the stability of other proteins, we have generated and evaluated over 70 TPP1 variants. The most effective mutation, R465G, increased the melting temperature of TPP1 from 55.6°C to 64.4°C and increased its enzymatic half-life at 60°C from 5.4 min to 21.9 min. However, the intracellular half-life of R465G and all other variants tested in cultured LINCL patient-derived lymphoblasts was similar to that of WT TPP1. These results provide structure/function insights into TPP1 and indicate that improving in vitro thermal stability alone is insufficient to generate TPP1 variants with improved physiological stability. This conclusion is supported by a proteome-wide analysis that indicates that lysosomal proteins have higher melting temperatures but also higher turnover rates than proteins of other organelles. These results have implications for similar efforts where protein engineering approaches, which are frequently evaluated in vitro, may be considered for improving the physiological properties of proteins, particularly those that function in the lysosomal environment.

Treatable Inherited Movement Disorders in Children: Spotlight on Clinical and Biochemical Features

Background

About 80% of monogenic metabolic diseases causing movement disorders (MDs) emerges during the first 2 decades of life, and a number of these conditions offers the opportunity of a disease-modifying treatment. The implementation of enlarged neonatal screening programs and the impressive rapid increase of the identification of new conditions are enhancing our potential to recognize and treat several diseases causing MDs, changing their outcome and phenotypic spectrum.

Methods and Findings

A literature review of monogenic disorders causing MDs amenable to treatment was conducted focusing on early clinical signs and diagnostic biomarkers. A classification in 3 broad categories based on the therapeutic approach has been proposed. Some disorders result in irreversible neurotoxic lesions that can only be prevented if treated in a presymptomatic stage, and others present with a progressive neurological impairment that a timely diagnosis and treatment may reverse or improve. Some MDs are the result of the failure of intracellular energy supply or altered glucose transport. The treatment in these conditions includes vitamins or a metabolic shift from a carbohydrate to a fatty acid catabolism, respectively. Finally, a group of highly treatable MDs are the result of defects of neurotransmitter metabolism. In these disorders, the supplementation of precursors or mimetics of neurotransmitters can deeply change the disease natural history.

Conclusions

To prevent serious and irreversible neurological impairment, the diagnostic work-up of MDs in children should consider a number of clinical red flags and biomarkers denoting specifically treatable diseases.

The expanding spectrum of movement disorders in genetic epilepsies

An ever-increasing number of neurogenetic conditions presenting with both epilepsy and atypical movements are now recognized. These disorders within the 'genetic epilepsy-dyskinesia' spectrum are clinically and genetically heterogeneous. Increased clinical awareness is therefore necessary for a rational diagnostic approach. Furthermore, careful interpretation of genetic results is key to establishing the correct diagnosis and initiating disease-specific management strategies in a timely fashion. In this review we describe the spectrum of movement disorders associated with genetically determined epilepsies. We also propose diagnostic strategies and putative pathogenic mechanisms causing these complex syndromes associated with both seizures and atypical motor control. WHAT THIS PAPER ADDS: Implicated genes encode proteins with very diverse functions. Pathophysiological mechanisms by which epilepsy and movement disorder phenotypes manifest are often not clear. Early diagnosis of treatable disorders is essential and next generation sequencing may be required.

Symmetric Age Association of Retinal Degeneration in Patients with CLN2-Associated Batten Disease

PURPOSE

Mutations in the CLN2 gene lead to a neurodegenerative and blinding lysosomal storage disorder: late infantile neuronal ceroid lipofucinosis, also known as "CLN2 disease." The purpose of the current study was to characterize the evolution of CLN2-associated retinal manifestations using the Weill Cornell Batten Scale (WCBS) and the age association of the retinal degeneration using central subfield thickness (CST) measurements and then correlate these findings with fundus photography and OCT to determine a critical period for retinal intervention.

DESIGN

Retrospective, single-center cohort.

PARTICIPANTS

Eighty-four eyes of 42 treatment-naïve patients with CLN2 disease.

METHODS

Clinical records, fundus photographs, and OCT imaging for patients with CLN2 disease collected during examinations under anesthesia were reviewed. Imaging was categorized per WCBS criteria by 3 masked graders.

MAIN OUTCOME MEASURES

CLN2-associated retinopathy assessed using WCBS scores, fundus photographs, and OCT imaging, correlated with patient age.

RESULTS

Eighty-four eyes of 42 patients had baseline fundus photographs, with baseline OCT in 31 eyes of 16 patients. Fundus photographs were obtained serially for 26 eyes of 13 patients, and serial OCT scans were obtained in 10 eyes of 5 patients. At baseline, bilateral WCBS scores were highly correlated for OCT and fundus photographs (r = 0.96 and 0.82, respectively). Central subfield thickness was negatively correlated with left and right eye WCBS OCT scores (r = -0.92 and -0.83, respectively; P < 0.001) and fundus photograph scores (r = -0.80 and -0.83, respectively; P < 0.001). OCT thickness was symmetrical between each eye. Baseline OCT data with age fit using a sigmoid function demonstrated a period of accelerated loss between 48 and 72 months of age.

CONCLUSIONS

Retinal degeneration associated with CLN2 disease manifests as a progressive, symmetrical decline, which appears to accelerate during a critical period at 48 to 72 months of age, suggesting intervention with retina-specific CLN2 gene therapy should occur ideally before or as early as possible within this critical period. The WCBS is a valuable tool and is highly correlated with the extent of retinal degeneration observed in OCT or fundus photographs; by using the fellow eye as a control, this grading scale can be used to monitor the effect of CLN2 gene therapy in future trials.

Mechanisms of action of currently used antiseizure drugs

Antiseizure drugs (ASDs) prevent the occurrence of seizures; there is no evidence that they have disease-modifying properties. In the more than 160 years that orally administered ASDs have been available for epilepsy therapy, most agents entering clinical practice were either discovered serendipitously or with the use of animal seizure models. The ASDs originating from these approaches act on brain excitability mechanisms to interfere with the generation and spread of epileptic hyperexcitability, but they do not address the specific defects that are pathogenic in the epilepsies for which they are prescribed, which in most cases are not well understood. There are four broad classes of such ASD mechanisms: (1) modulation of voltage-gated sodium channels (e.g. phenytoin, carbamazepine, lamotrigine), voltage-gated calcium channels (e.g. ethosuximide), and voltage-gated potassium channels [e.g. retigabine (ezogabine)]; (2) enhancement of GABA-mediated inhibitory neurotransmission (e.g. benzodiazepines, tiagabine, vigabatrin); (3) attenuation of glutamate-mediated excitatory neurotransmission (e.g. perampanel); and (4) modulation of neurotransmitter release via a presynaptic action (e.g. levetiracetam, brivaracetam, gabapentin, pregabalin). In the past two decades there has been great progress in identifying the pathophysiological mechanisms of many genetic epilepsies. Given this new understanding, attempts are being made to engineer specific small molecule, antisense and gene therapies that functionally reverse or structurally correct pathogenic defects in epilepsy syndromes. In the near future, these new therapies will begin a paradigm shift in the treatment of some rare genetic epilepsy syndromes, but targeted therapies will remain elusive for the vast majority of epilepsies until their causes are identified. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Blood-Brain Barrier and Delivery of Protein and Gene Therapeutics to Brain

Alzheimer’s disease (AD) and treatment of the brain in aging require the development of new biologic drugs, such as recombinant proteins or gene therapies. Biologics are large molecule therapeutics that do not cross the blood-brain barrier (BBB). BBB drug delivery is the limiting factor in the future development of new therapeutics for the brain. The delivery of recombinant protein or gene medicines to the brain is a binary process: either the brain drug developer re-engineers the biologic with BBB drug delivery technology, or goes forward with brain drug development in the absence of a BBB delivery platform. The presence of BBB delivery technology allows for engineering the therapeutic to enable entry into the brain across the BBB from blood. Brain drug development may still take place in the absence of BBB delivery technology, but with a reliance on approaches that have rarely led to FDA approval, e.g., CSF injection, stem cells, small molecules, and others. CSF injection of drug is the most widely practiced approach to brain delivery that bypasses the BBB. However, drug injection into the CSF results in limited drug penetration to the brain parenchyma, owing to the rapid export of CSF from the brain to blood. A CSF injection of a drug is equivalent to a slow intravenous (IV) infusion of the pharmaceutical. Given the profound effect the existence of the BBB has on brain drug development, future drug or gene development for the brain will be accelerated by future advances in BBB delivery technology in parallel with new drug discovery.

Future perspectives: What lies ahead for Neuronal Ceroid Lipofuscinosis research?

Progress is being made in all aspects of Neuronal Ceroid Lipofuscinosis (NCL) research, resulting in many recent advances. These advances encompass several areas that were previously thought intractable, ranging from basic science, through to a better understanding of the clinical presentation of different forms of NCL, therapeutic development, and new clinical trials that are underway. Increasing numbers of original NCL research papers continue to be published, and this new sense of momentum is greatly encouraging for the field. Here, we make some predictions as to what we can anticipate in the next few years.

The concept of disease modification

Traditionally treatment of epileptic seizures has been symptomatic, namely medication has been targeted at raising the threshold to the occurrence of epileptic seizures. This has had little impact on the rate of drug resistance over time, or impact on comorbidities such as learning and behaviour particularly in the early onset epilepsies. The advent of advanced neuroimaging and genomics has revealed the cause of the epilepsy in a much higher percentage, and advanced our knowledge as to the underlying pathophysiology. This has given us the opportunity to turn to the possibility of interventional treatment, targeting the underlying cause, and consequently the possibility of changing the natural history of disease. Here we review the options open to us, and the evidence to date.

A multi-disciplinary clinic for SCN8A-related epilepsy

OBJECTIVE

We endeavored to evaluate a cohort of patients diagnosed with SCN8A-related epilepsy in a multi-disciplinary clinic and to create a bio-repository.

METHODS

We recruited patients with epilepsy due to SCN8A variants at Children's National Medical Center, through family organizations, or SCN8A.net. Study procedures included medical record review, review of EEG and MRI data, clinical evaluation, the Vineland Adaptive Behavior Scales, Third Edition (VABS-3), DNA extraction, and preparation of peripheral blood mononuclear cells.

RESULTS

Seventeen patients (9 months - 19 years) completed the study. Age at seizure onset was 1 day to 4 years old (median age 4 months). Epilepsy phenotype ranged from mild epilepsy to severe developmental and epileptic encephalopathy. Medications targeting the voltage-gated sodium channel were most often effective, while levetiracetam resulted in worsening seizures and/or developmental regression in 7/16 (p < 0.05). VABS-3 scores were below age expectations for most children; older children had lower scores. Neurological examination revealed hypotonia (13), spastic quadriparesis (1), ataxia (9), dyskinesia (2)/ dystonia (7), and four non-ambulatory.

CONCLUSIONS

This is the first report of a large series of patients with epilepsy due to SCN8A variants evaluated in a single multi-disciplinary clinic. By utilizing a more comprehensive and consistent evaluation, we clarify specific seizure and epilepsy types, describe a distinct epilepsy phenotype in a patient with a nonsense variant, delineate patterns of developmental delay, language, and swallow function (specifically anomic aphasia and flaccid dysarthria), identify and characterize movement disorders, report common findings on physical exam, and demonstrate clinical worsening with levetiracetam.

Cardiac pathology in neuronal ceroid lipofuscinoses (NCL): More than a mere co-morbidity

The neuronal ceroid lipofuscinoses (NCLs) are mostly seen as diseases affecting the central nervous system, but there is accumulating evidence that they have co-morbidities outside the brain. One of these co-morbidities is a decline in cardiac function. This is becoming increasingly recognised in teenagers and adolescents with juvenile CLN3, but it may also occur in individuals with other NCLs. The purpose of this review is to summarise the current knowledge of the structural and functional changes found in the hearts of animal models and people diagnosed with NCL. In addition, we present evidence of structural changes that were observed in a systematic comparison of the cardiomyocytes from CLN3^Δex7/8 mice.

Neurofilament light is a treatment-responsive biomarker in CLN2 disease

OBJECTIVE

Neuronal ceroid lipofuscinosis type 2 (CLN2 disease) is a rare, progressive, fatal neurodegenerative pediatric disorder resulting from deficiencies of the lysosomal enzyme tripeptidyl peptidase 1 that are caused by mutations in TPP1. Identifying biomarkers of CLN2 disease progression will be important in assessing the efficacy of therapeutic interventions for this disorder. Neurofilament light is an intrinsic component of healthy neurons; elevated circulating extracellular neurofilament light is a biomarker of neuropathology in several adult-onset neurological diseases. Our objective was to assess whether circulating neurofilament light is a biomarker that is responsive to enzyme replacement therapy (ERT) in CLN2 disease.

METHODS

Using an ultrasensitive immunoassay, we assessed plasma neurofilament light changes during disease progression in a canine model of CLN2 disease and in ERT clinical trial CLN2 disease patients.

RESULTS

In tripeptidyl peptidase 1 (TPP1)-null dogs (N = 11), but not in control dogs [N = 6 (TPP1^+/- ) and N = 27 (WT)], neurofilament light levels increased more than tenfold above initial low baseline levels during disease progression. Before treatment in 21 human subjects with CLN2 disease (age range: 1.72-6.85 years), neurofilament light levels were 48-fold higher (P < 0.001) than in 7 pediatric controls (age range: 8-11 years). Pretreatment neurofilament light did not significantly correlate with disease severity or age. In CLN2 disease subjects receiving ERT, neurofilament light levels decreased by 50% each year over more than 3 years of treatment.

INTERPRETATION

Our data indicate that circulating neurofilament light is a treatment-responsive biomarker in CLN2 disease and could contribute to understanding of the pathophysiology of this devastating pediatric disorder.

Clinical approach to neurodegenerative disorders in childhood: an updated overview

Neurodegenerative disorders include a group of severe diseases that share a core including a gradual loss of previously acquired motor, sensory and cognitive functions. In pediatric age, the main diagnostic issues are the discrimination between the loss of previously acquired competencies and the lack of achievement of specific developmental milestones. An ideal classification of these disorders could be based on the combination of genetic, clinical and neuroimaging features. Diagnostic workup should be organized with a special attention to the few diseases with an available and effective therapeutic treatment. The present paper reports a proposal of classification that is based on the prominently involved structure and summarizes the hallmarks for clinical approach and therapeutic management.

Advances in the Treatment of Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinoses (NCL) represent a class of neurodegenerative disorders involving defective lysosomal processing enzymes or receptors, leading to lysosomal storage disorders, typically characterized by observation of cognitive and visual impairments, epileptic seizures, ataxia, and deterioration of motor skills. Recent success of a biologic (Brineura®) for the treatment of neurologic manifestations of the central nervous system (CNS) has led to renewed interest in therapeutics for NCL, with the goal of ablating or reversing the impact of these devastating disorders. Despite complex challenges associated with CNS therapy, many treatment modalities have been evaluated, including enzyme replacement therapy, gene therapy, stem cell therapy, and small molecule pharmacotherapy. Because the clinical endpoints for the evaluation of candidate therapies are complex and often reliant on subjective clinical scales, the development of quantitative biomarkers for NCLs has become an apparent necessity for the validation of potential treatments. We will discuss the latest findings in the search for relevant biomarkers for assessing disease progression. For this review, we will focus primarily on recent pre-clinical and clinical developments for treatments to halt or cure these NCL diseases. Continued development of current therapies and discovery of newer modalities will be essential for successful therapeutics for NCL.

AREAS COVERED

The reader will be introduced to the NCL subtypes, natural histories, experimental animal models, and biomarkers for NCL progression; challenges and different therapeutic approaches, and the latest pre-clinical and clinical research for therapeutic development for the various NCLs. This review corresponds to the literatures covering the years from 1968 to mid-2019, but primarily addresses pre-clinical and clinical developments for the treatment of NCL disease in the last decade and as a follow-up to our 2013 review of the same topic in this journal.

EXPERT OPINION

Much progress has been made in the treatment of neurologic diseases, such as the NCLs, including better animal models and improved therapeutics with better survival outcomes. Encouraging results are being reported at symposiums and in the literature, with multiple therapeutics reaching the clinical trial stage for the NCLs. The potential for a cure could be at hand after many years of trial and error in the preclinical studies. The clinical development of enzyme replacement therapy (Brineura® for CLN2), immunosuppression (CellCept® for CLN3), and gene therapy vectors (for CLN1, CLN2, CLN3, and CLN6) are providing encouragement to families that have a child afflicted with NCL. We believe that successful therapies in the future may involve the combination of two or more therapeutic modalities to provide therapeutic benefit especially as the patients grow older.

The contribution of multicellular model organisms to neuronal ceroid lipofuscinosis research

The NCLs (neuronal ceroid lipofuscinosis) are forms of neurodegenerative disease that affect people of all ages and ethnicities but are most prevalent in children. Commonly known as Batten disease, this debilitating neurological disorder is comprised of 13 different subtypes that are categorized based on the particular gene that is mutated (CLN1-8, CLN10-14). The pathological mechanisms underlying the NCLs are not well understood due to our poor understanding of the functions of NCL proteins. Only one specific treatment (enzyme replacement therapy) is approved, which is for the treating the brain in CLN2 disease. Hence there remains a desperate need for further research into disease-modifying treatments. In this review, we present and evaluate the genes, proteins and studies performed in the social amoeba, nematode, fruit fly, zebrafish, mouse and large animals pertinent to NCL. In particular, we highlight the use of multicellular model organisms to study NCL protein function, pathology and pathomechanisms. Their use in testing novel therapeutic approaches is also presented. With this information, we highlight how future research in these systems may be able to provide new insight into NCL protein functions in human cells and aid in the development of new therapies.

Juvenile Batten Disease (CLN3): Detailed Ocular Phenotype, Novel Observations, Delayed Diagnosis, Masquerades, and Prospects for Therapy

Purpose

To characterize the retinal phenotype of juvenile neuronal ceroid lipofuscinosis (JNCL), highlight delayed and mistaken diagnosis, and propose an algorithm for early identification.

Design

Retrospective case series.

Participants

Eight children (5 female) with JNCL.

Methods

Review of clinical notes, retinal imaging including fundus autofluorescence and OCT, electroretinography (ERG), and both microscopy and molecular genetic testing.

Main Outcome Measurements

Demographic data, signs and symptoms, visual acuity (VA), fundus autofluorescence and OCT findings, ERG phenotype, and microscopy/molecular genetics.

Results

Participants presented with rapid bilateral vision loss over 1 to 18 months, with mean VA deteriorating from 0.44 logarithm of the minimum angle of resolution (logMAR) (range, 0.20–1.78 logMAR) at baseline to 1.34 logMAR (0.30 logMAR - light perception) at last follow-up. Age of onset ranged from 3 to 7 years (mean, 5.3 years). The age at diagnosis of JNCL ranged from 7 to 10 years (mean, 8.3 years). Six children displayed eccentric fixation, and 6 children had cognitive or neurologic signs at the time of diagnosis (75%). Seven patients had bilateral bull’s-eye maculopathy at presentation. Coats-like exudative vasculopathy, not previously reported in JNCL, was observed in 1 patient. OCT imaging revealed near complete loss of outer retinal layers and marked atrophy of the nerve fiber and ganglion cell layers at the central macula. An electronegative ERG was present in 4 patients (50%), but with additional a-wave reduction, there was an undetectable ERG in the remaining 4 patients. Blood film microscopy revealed vacuolated lymphocytes, and electron microscopy showed lysosomal (fingerprint) inclusions in all 8 patients.

Conclusions

In a young child with bilateral rapidly progressive vision loss and macular disturbance, blood film microscopy to detect vacuolated lymphocytes is a rapid, readily accessible, and sensitive screening test for JNCL. Early suspicion of JNCL can be aided by detailed directed history and high-resolution retinal imaging, with subsequent targeted microscopy/genetic testing. Early diagnosis is critical to ensure appropriate management, counseling, support, and social care for children and their families. Furthermore, although potential therapies for this group of disorders are in early-phase clinical trial, realistic expectations are that successful intervention will be most effective when initiated at the earliest stage of disease.

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.

Neuronal network dysfunction precedes storage and neurodegeneration in a lysosomal storage disorder

Accumulation of lysosomal storage material and late-stage neurodegeneration are hallmarks of lysosomal storage disorders (LSDs) affecting the brain. Yet, for most LSDs, including CLN3 disease, the most common form of childhood dementia, it is unclear what mechanisms drive neurologic symptoms. Do deficits arise from loss of function of the mutated protein or toxicity from storage accumulation? Here, using in vitro voltage-sensitive dye imaging and in vivo electrophysiology, we find progressive hippocampal dysfunction occurs before notable lysosomal storage and neuronal loss in 2 CLN3 disease mouse models. Pharmacologic reversal of lysosomal storage deposition in young mice does not rescue this circuit dysfunction. Additionally, we find that CLN3 disease mice lose an electrophysiologic marker of new memory encoding - hippocampal sharp-wave ripples. This discovery, which is also seen in Alzheimer's disease, suggests the possibility of a shared electrophysiologic signature of dementia. Overall, our data describe new insights into previously unknown network-level changes occurring in LSDs affecting the central nervous system and highlight the need for new therapeutic interventions targeting early circuit defects.

Analysis of Brain and Cerebrospinal Fluid from Mouse Models of the Three Major Forms of Neuronal Ceroid Lipofuscinosis Reveals Changes in the Lysosomal Proteome

Treatments are emerging for the neuronal ceroid lipofuscinoses (NCLs), a group of similar but genetically distinct lysosomal storage diseases. Clinical ratings scales measure long-term disease progression and response to treatment but clinically useful biomarkers have yet to be identified in these diseases. We have conducted proteomic analyses of brain and cerebrospinal fluid (CSF) from mouse models of the most frequently diagnosed NCL diseases: CLN1 (infantile NCL), CLN2 (classical late infantile NCL) and CLN3 (juvenile NCL). Samples were obtained at different stages of disease progression and proteins quantified using isobaric labeling. In total, 8303 and 4905 proteins were identified from brain and CSF, respectively. We also conduced label-free analyses of brain proteins that contained the mannose 6-phosphate lysosomal targeting modification. In general, we detect few changes at presymptomatic timepoints but later in disease, we detect multiple proteins whose expression is significantly altered in both brain and CSF of CLN1 and CLN2 animals. Many of these proteins are lysosomal in origin or are markers of neuroinflammation, potentially providing clues to underlying pathogenesis and providing promising candidates for further validation.

Lysosomal storage disorders: pathology within the lysosome and beyond

This Preface introduces the articles of the special issue on "Lysosomal Storage Disorders" in which several recognized experts provide an overview of this research field. Lysosomes were first described in the 1950s and recognized for their role in substrate degradation and recycling. Because lysosomes impact numerous fundamental homeostatic processes, research on lysosomal storage disorders (LSDs) is crucial to advance our understanding of this intriguing organelle. This Special Issue highlights some of the LSDs that impact the central nervous system (CNS) as well as comprehensive overviews of lysosomal biology, CNS metabolism, and sphingolipid biosynthesis and turnover, all of which are critical toward our understanding of normal lysosomal function and how this is perturbed in the context of LSDs. This is the Preface for the special issue "Lysosomal Storage Disorders". Cover Image for this issue: doi: 10.1111/jnc.14496.

Mice deficient in the lysosomal enzyme palmitoyl-protein thioesterase 1 (PPT1) display a complex retinal phenotype

Neuronal ceroid lipofuscinosis (NCL) type 1 (CLN1) is a neurodegenerative storage disorder caused by mutations in the gene encoding the lysosomal enzyme palmitoyl-protein thioesterase 1 (PPT1). CLN1 patients suffer from brain atrophy, mental and motor retardation, seizures, and retinal degeneration ultimately resulting in blindness. Here, we performed an in-depth analysis of the retinal phenotype of a PPT1-deficient mouse, an animal model of this condition. Reactive astrogliosis and microgliosis were evident in mutant retinas prior to the onset of retinal cell loss. Progressive accumulation of storage material, a pronounced dysregulation of various lysosomal proteins, and accumulation of sequestosome/p62-positive aggregates in the inner nuclear layer also preceded retinal degeneration. At advanced stages of the disease, the mutant retina was characterized by a significant loss of ganglion cells, rod and cone photoreceptor cells, and rod and cone bipolar cells. Results demonstrate that PPT1 dysfunction results in early-onset pathological alterations in the mutant retina, followed by a progressive degeneration of various retinal cell types at relatively late stages of the disease. Data will serve as a reference for future work aimed at developing therapeutic strategies for the treatment of retinal degeneration in CLN1 disease.