Study of Intraventricular Cerliponase Alfa for CLN2 Disease.

BACKGROUND: Recombinant human tripeptidyl peptidase 1 (cerliponase alfa) is an enzyme-replacement therapy that has been developed to treat neuronal ceroid lipofuscinosis type 2 (CLN2) disease, a rare lysosomal disorder that causes progressive dementia in children. METHODS: In a multicenter, open-label study, we evaluated the effect of intraventricular infusion of cerliponase alfa every 2 weeks in children with CLN2 disease who were between the ages of 3 and 16 years. Treatment was initiated at a dose of 30 mg, 100 mg, or 300 mg; all the patients then received the 300-mg dose for at least 96 weeks. The primary outcome was the time until a 2-point decline in the score on the motor and language domains of the CLN2 Clinical Rating Scale (which ranges from 0 to 6, with 0 representing no function and 3 representing normal function in each of the two domains), which was compared with the time until a 2-point decline in 42 historical controls. We also compared the rate of decline in the motor-language score between the two groups, using data from baseline to the last assessment with a score of more than 0, divided by the length of follow-up (in units of 48 weeks). RESULTS: Twenty-four patients were enrolled, 23 of whom constituted the efficacy population. The median time until a 2-point decline in the motor-language score was not reached for treated patients and was 345 days for historical controls. The mean (±SD) unadjusted rate of decline in the motor-language score per 48-week period was 0.27±0.35 points in treated patients and 2.12±0.98 points in 42 historical controls (mean difference, 1.85; P<0.001). Common adverse events included convulsions, pyrexia, vomiting, hypersensitivity reactions, and failure of the intraventricular device. In 2 patients, infections developed in the intraventricular device that was used to administer the infusion, which required antibiotic treatment and device replacement. CONCLUSIONS: Intraventricular infusion of cerliponase alfa in patients with CLN2 disease resulted in less decline in motor and language function than that in historical controls. Serious adverse events included failure of the intraventricular device and device-related infections. (Funded by BioMarin Pharmaceutical and others; CLN2 ClinicalTrials.gov numbers, NCT01907087 and NCT02485899 .).

First Recognized Patient with Genetic Vitamin E Deficiency Stable after 36 Years of Controlled Supplement Therapy.

INTRODUCTION: Familial isolated deficiency of vitamin E (VED or AVED; MIM #277460) is a progressive neurodegenerative disorder resembling Friedreich ataxia. It is caused by the deficiency of α-tocopherol transfer protein that prevents patients from retaining vitamin E. Oral vitamin E supplements are an accepted treatment, but detailed dosage recommendations and reports on long-term therapeutic results are scarce. METHODS: The first patient with VED was discovered at our institution at the age of 12 years and has since been followed with clinical, neurophysiological, neuroradiological, and biochemical investigations to his present age of 52 years. For the last 36 years, the patient has scrupulously followed a custom-made high-dose vitamin E supplement regimen that we devised on the basis of studies of his metabolism of vitamin E. RESULTS: Over the long period of observation, the patient has remained in good general health and has not shown progression of neurological symptoms and signs. His vitamin E plasma levels were always moderately above the normal range. During short interruptions of vitamin E supplements, vitamin E levels fell rapidly, even after years of massive supplementation. DISCUSSION: In this VED patient, a specified and carefully controlled high-dose vitamin E therapy has prevented any recognizable progression of the neurodegenerative process over more than 3 decades of observation.

A recurrent de novo mutation in TMEM106B causes hypomyelinating leukodystrophy.

Hypomyelinating leukodystrophies are a heterogeneous group of disorders with a clinical presentation that often includes early-onset nystagmus, ataxia and spasticity and a wide range of severity. Using next-generation sequencing techniques and GeneMatcher, we identified four unrelated patients with brain hypomyelination, all with the same recurrent dominant mutation, c.754G>A p.(Asp252Asn), in TMEM106B. The mutation was confirmed as de novo in three of the cases, and the mildly affected father of the fourth affected individual was confirmed as mosaic for this variant. The protein encoded by TMEM106B is poorly characterized but is reported to have a role in regulation of lysosomal trafficking. Polymorphisms in TMEM106B are thought to modify disease onset in frontotemporal dementia, but its relation to myelination is not understood. Clinical presentation in three of the four patients is remarkably benign compared to other hypomyelinating disorders, with congenital nystagmus and mild motor delay. These findings add TMEM106B to the growing list of genes causing hypomyelinating disorders and emphasize the essential role lysosomes play in myelination.

Reprint of "Ethical issues with artificial nutrition of children with degenerative brain diseases".

This report highlights viewpoints of the authors and comments from the auditory at a workshop, held during the 14th international Congress on neuronal ceroid lipofuscinoses (NCL) in Córdoba, Argentina, on ethical aspects of artificial nutrition in children with degenerative brain diseases. The discussion centers on what constitutes the best interest of a patient whose personality was immature before the onset of the disease, who has become demented during its course and is unable to communicate his/her own positions and desires. There is wide consensus that in a child with advanced disease who cannot be fed naturally, decisions to withhold nutrition or to institute or stop artificial nutrition, should only be made by parents (or their representatives) who are adequately prepared on an intellectual and emotional level. We try to show that such decisions are highly individual but can be made in a rationally and emotionally acceptable way after a careful and prolonged dialogue between families and professionals. A checklist summarizes important considerations. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

Ethical issues with artificial nutrition of children with degenerative brain diseases.

This report highlights viewpoints of the authors and comments from the auditory at a workshop, held during the 14th international Congress on neuronal ceroid lipofuscinoses (NCL) in Córdoba, Argentina, on ethical aspects of artificial nutrition in children with degenerative brain diseases. The discussion centers on what constitutes the best interest of a patient whose personality was immature before the onset of the disease, who has become demented during its course and is unable to communicate his/her own positions and desires. There is wide consensus that in a child with advanced disease who cannot be fed naturally, decisions to withhold nutrition or to institute or stop artificial nutrition, should only be made by parents (or their representatives) who are adequately prepared on an intellectual and emotional level. We try to show that such decisions are highly individual but can be made in a rationally and emotionally acceptable way after a careful and prolonged dialogue between families and professionals. A checklist summarizes important considerations. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

CLN2 Disease (Classic Late Infantile Neuronal Ceroid Lipofuscinosis).

CLN2 disease is an inherited metabolic storage disorder caused by the deficiency of the lysosomal enzyme tripeptidyl peptidase 1 (TPP1). The disease affects mainly the brain and the retina and is characterized by progressive dysfunction of the central nervous system, leading to dementia, epilepsy, loss of motor function and blindness. The classical late infantile type begins at around three years of age with epilepsy and/or a standstill of psychomotor development, followed by a rapid loss of all abilities and death in childhood. A late onset form in a small proportion of patients starts at the age of 4 to 10 years, but also leads to severe neurological deterioration. The deficiency of TPP1 causes the lysosomal accumulation of a material called ceroid lipofuscin. The natural substrate of TPP1 is not known, nor is the connection between storage process and neurodegeneration, which is characterized by loss of neurons. Among various experimental approaches to treatment, enzyme replacement therapy (ERT) and gene therapy have developed remarkably. Enzyme delivery through the cerebrospinal fluid led to wide distribution of enzyme activity in the brain and to attenuated neuropathology and disease progression in a TPP1-deficient mouse model as well as in a natural TPP1-deficient dog model. Safety of the intrathecal delivery, pharmacokinetics, and tissue distribution of the administered enzyme studied in non-human primates were encouraging, and a phase I/II clinical trial for intraventricular ERT in CLN2 patients is ongoing. A second approach uses intracerebral injection of viral vectors containing normal coding segments of the CLN2 gene. In a CLN2 mouse model, this procedure resulted in cerebral enzyme expression, reduced brain pathology and increased survival. A small number of patients have been treated the same way using an AAV2-vector for gene transfer to the brain. Although there were no serious adverse events unequivocally attributable to the vector used, there were some serious adverse effects, and a clinical benefit was not clearly evident under the conditions of the experiment. A phase I/phase II study using a AAVrh10 vector is presently recruiting patients.

Mutations in ROGDI Cause Kohlschütter-Tönz Syndrome.

Kohlschütter-Tönz syndrome (KTS) is an autosomal-recessive disease characterized by the combination of epilepsy, psychomotor regression, and amelogenesis imperfecta. The molecular basis has not yet been elucidated. Here, we report that KTS is caused by mutations in ROGDI. Using a combination of autozygosity mapping and exome sequencing, we identified a homozygous frameshift deletion, c.229_230del (p.Leu77Alafs(∗)64), in ROGDI in two affected individuals from a consanguineous family. Molecular studies in two additional KTS-affected individuals from two unrelated Austrian and Swiss families revealed homozygosity for nonsense mutation c.286C>T (p.Gln96(∗)) and compound heterozygosity for the splice-site mutations c.531+5G>C and c.532-2A>T in ROGDI, respectively. The latter mutation was also found to be heterozygous in the mother of the Swiss affected individual in whom KTS was reported for the first time in 1974. ROGDI is highly expressed throughout the brain and other organs, but its function is largely unknown. Possible interactions with DISC1, a protein involved in diverse cytoskeletal functions, have been suggested. Our finding that ROGDI mutations cause KTS indicates that the protein product of this gene plays an important role in neuronal development as well as amelogenesis.

Hypomyelinating leukodystrophies: translational research progress and prospects.

Hypomyelinating leukodystrophies represent a genetically heterogeneous but clinically overlapping group of heritable disorders. Current management approaches in the care of the patient with a hypomyelinating leukodystrophy include use of serial magnetic resonance imaging (MRI) to establish and monitor hypomyelination, molecular diagnostics to determine a specific etiology, and equally importantly, careful attention to neurologic complications over time. Emerging research in oligodendrocyte biology and neuroradiology with bedside applications may result in the possibility of clinical trials in the near term, yet there are significant gaps in knowledge in disease classification, characterization, and outcome measures in this group of disorders. Here we review the biological background of myelination, the clinical and genetic variability in hypomyelinating leukodystrophies, and the insights that can be obtained from current MRI techniques. In addition, we discuss ongoing research approaches to define potential outcome markers for future clinical trials.

Early-onset leukoencephalopathy due to a homozygous missense mutation in the DARS2 gene.

Mutations in the DARS2 gene are known to cause leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL), a rare autosomal recessive neurological disorder. It was originally described as juvenile-onset slowly progressive ataxia and spasticity, but recent reports suggest a broader clinical spectrum. Most patients were found to carry compound heterozygous DARS2 mutations, and only very few patients with homozygous mutations have been described so far. We present here an 8-month-old boy carrying a homozygous missense mutation in DARS2 who clinically showed severe neurological deterioration after a respiratory tract infection, followed by an almost complete remission of symptoms. This report further extends the knowledge about the clinical and molecular genetic spectrum of LBSL.

Phenotyping heterozygous carriers of juvenile neuronal ceroid lipofuscinosis with CLN3 mutations.

PURPOSE: The objective of this study was to establish an ophthalmologic phenotype of heterozygous carriers of juvenile neuronal ceroid lipofuscinosis (CLN3 disease, Batten disease). METHODS: The eyes and vision of nine heterozygous carriers of juvenile neuronal ceroid lipofuscinosis with classical CLN3 mutations were examined using the following methods: clinical examination, visual acuity, ophthalmoscopy, optical coherence tomography (macular thickness and peripapillary retinal nerve fibre layer measurement [RNFL]), fundus autofluorescence measurement, infrared imaging, and full-field and multifocal electroretinogram. Optical coherence tomography and electrophysiological data were statistically compared with age- and sex-matched control groups. RESULTS: The basic clinical examination as well as the fundus autofluorescence and infrared images of the macular region were unremarkable. Neither the electrophysiological examinations nor optical coherence tomography yielded fundamental abnormalities. There were only two significant-albeit most likely clinically irrelevant-differences that occurred in comparison to the control group: a decrease in RNFL of the nasal quadrant in the OCT and a prolongation of the N1 implicit time of the second-ring eccentricity in the multifocal electroretinogram. CONCLUSIONS: The eyes and vision of heterozygous carriers of CLN3 disease showed normal features when compared to a control group, which controverts a previously suggested retinal dysfunction in these subjects.

NCL diseases - clinical perspectives.

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage disorders and together are the most common degenerative brain diseases in childhood. They are a group of disorders linked by the characteristic accumulation of abnormal storage material in neurons and other cell types, and a degenerative disease course. All NCLs are characterized by a combination of dementia, epilepsy, and motor decline. For most childhood NCLs, a progressive visual failure is also a core feature. The characteristics of these symptoms can vary and the age at disease onset ranges from birth to young adulthood. Genetic heterogeneity, with fourteen identified NCL genes and wide phenotypic variability render diagnosis difficult. A new NCL classification system based on the affected gene and the age at disease onset allows a precise and practical delineation of an individual patient's NCL type. A diagnostic algorithm to identify each NCL form is presented here. Precise NCL diagnosis is essential not only for genetic counseling, but also for the optimal delivery of care and information sharing with the family and other caregivers. These aspects are challenging because there are also potential long term complications which are specific to NCL type. Therefore care supported by a specifically experienced team of clinicians is recommended. As the underlying pathophysiological mechanism is still unclear for all NCL forms, the development of curative therapies remains difficult. This article is part of a Special Issue entitled: The neuronal ceroid lipofuscinoses or Batten Disease.

Unexplained loss of vision in a child: consider bilateral primary optic nerve sheath meningioma.

A 4-year-old girl gradually lost her vision to become practically blind at the age of 10 years. Examinations at several medical centers had been unable to establish an etiology. Traditional investigation using cerebral magnetic resonance imaging (MRI) initially showed normal results; however, later on it showed progressive atrophy of both optical nerves without recognizable cause. Subsequently, MRI including adequate orbital sequences, contrast-enhanced sequences, and fat suppression demonstrated bilateral primary optic nerve sheath meningioma, a rare but treatable tumor of childhood. The patient underwent neurosurgery and to date retains minimal vision. Adequate neuroradiological investigation of unexplained optic atrophy is advocated.

Imaging evidence of early brain tissue degeneration in patients with vanishing white matter disease: a multimodal MR study.

To find imaging signs of active degenerative processes in vanishing white matter disease (VWM), six VWM patients and six matched controls underwent MR examinations. The data were analyzed with modified Scheltens scales for morphological findings and determined quantitatively for apparent diffusion coefficient (ADC). Single-voxel MR spectra were acquired at the parietal white matter and analyzed with LCModel. Typical VWM brain lesions were found in all patients accompanied by proton diffusion abnormalities: Increased ADC appeared in brain regions with severe myelin destruction in all patients, and reduced ADC in two of six younger patients in remaining white matter adjacent to the lesions or at the borders around the lesions, who had a short history of the disease (≤ 1 year). The MR spectroscopy revealed reductions of NAA, Cho, and Cr, which correlate to the grade of white matter abnormalities. An increase of myo-inositol as marker of reactive gliosis was missing. Thus, restricted proton diffusion was evident in younger VWM patients with short history of disease, which in combination with lack of reactive gliosis may reflect early white matter degeneration in VWM. The multimodal MR methods are useful for characterizing such tissue degeneration in brain in vivo.

Analysis of potential biomarkers and modifier genes affecting the clinical course of CLN3 disease.

Mutations in the CLN3 gene lead to juvenile neuronal ceroid lipofuscinosis, a pediatric neurodegenerative disorder characterized by visual loss, epilepsy and psychomotor deterioration. Although most CLN3 patients carry the same 1-kb deletion in the CLN3 gene, their disease phenotype can be variable. The aims of this study were to (i) study the clinical phenotype in CLN3 patients with identical genotype, (ii) identify genes that are dysregulated in CLN3 disease regardless of the clinical course that could be useful as biomarkers, and (iii) find modifier genes that affect the progression rate of the disease. A total of 25 CLN3 patients homozygous for the 1-kb deletion were classified into groups with rapid, average or slow disease progression using an established clinical scoring system. Genome-wide expression profiling was performed in eight CLN3 patients with different disease progression and matched controls. The study showed high phenotype variability in CLN3 patients. Five genes were dysregulated in all CLN3 patients and present candidate biomarkers of the disease. Of those, dual specificity phosphatase 2 (DUSP2) was also validated in acutely CLN3-depleted cell models and in CbCln3(Δex7/8) cerebellar precursor cells. A total of 13 genes were upregulated in patients with rapid disease progression and downregulated in patients with slow disease progression; one gene showed dysregulation in the opposite way. Among these potential modifier genes, guanine nucleotide exchange factor 1 for small GTPases of the Ras family (RAPGEF1) and transcription factor Spi-B (SPIB) were validated in an acutely CLN3-depleted cell model. These findings indicate that differential perturbations of distinct signaling pathways might alter disease progression and provide insight into the molecular alterations underlying neuronal dysfunction in CLN3 disease and neurodegeneration in general.

Ethical Issues in Care and Treatment of Neuronal Ceroid Lipofuscinoses (NCL)-A Personal View.

The management of Neuronal Ceroid Lipofuscinoses (NCL), a group of genetic neurodegenerative disorders mainly affecting brain and retinas, raises difficult questions for physicians and other professionals in research, pharmaceutical industry, and public health. Ethical problems in medicine cannot be solved by rational deliberation or by following formal rules. Two topics of ethical issues in the field of NCL are presented here. One group relates to the care of individual patients and centers on a life with dementia at a young age. Advanced care planning for the end of life and the use of life-prolonging measures require challenging assumptions in the best interest of a patient. A second group of questions relates to new treatments. Impressive novel putative causal therapies, such as enzyme replacement for CLN2 disease, may be only disease-modifying and carry the risk of changing a deadly disease of short duration into one with prolonged survival and poor quality of life. The wish for better therapeutic interventions in life-limiting diseases has to take such risks, but more experience is needed before definite conclusions can be drawn. The appropriateness of presymptomatic screening for a severe disease, e.g., must be carefully evaluated to avoid the disastrous experience made with the rash start of newborn screening for Krabbe disease. The ethical issues described and commented in the article reflect the personal experience of a pediatrician who has studied clinical and research questions in NCL for four decades. They should alert various professionals to the necessity of taking their own decisions in situations that are caused by rare progressive brain diseases of young persons, as typified by the NCL.

[Ophthalmological manifestations of neuronal ceroid lipofuscinoses (NCL) : NCL as diseases of brain and retina-the role of ophthalmologists]. / Ophthalmologische Manifestationen bei neuronalen Ceroid-Lipofuszinosen (NCL) : NCL als Erkrankungen von Retina und Gehirn ­ Rolle der Augenärzte.

BACKGROUND: Neuronal ceroid lipofuscinoses are hereditary lysosomal storage diseases, which lead to a progressive neurodegeneration of the brain and retina. Visual loss can be the initial symptom but can also occur later in the course of the disease. OBJECTIVE: The aim of this article is to provide ophthalmologists with an overview of the characteristic ocular alterations and the general disease course of the 13 currently known various forms of NCL. MATERIAL AND METHODS: The findings from predominantly clinical articles are reviewed and summarized. RESULTS AND CONCLUSION: Retinal degeneration plays a crucial role in this group of neurodegenerative diseases. In several forms visual decline is the initial clinical symptom in affected patients. Therefore, the ophthalmologist is the first medical expert consulted. An early diagnosis is crucial for the future personal and family planning but is also important regarding upcoming therapeutic strategies, which might be much more effective in patients with early stage disease. When the presence of retinal degeneration due to an NCL disease is suspected an immediate genetic diagnostic confirmation and collaboration with neuropediatricians is recommended.

Enzymatic diagnosis of neuronal lipofuscinoses in dried blood spots using substrates for concomitant tandem mass spectrometry and fluorimetry.

Neuronal ceroid lipofuscinoses (NCLs) are a group of neurodegenerative diseases predominantly in childhood that are characterized by psychomotor deterioration, epilepsy, and early death of patients. The NCLs analyzed in the present study are caused by defects of the specific enzymes, CLN1 (palmitoyl protein thioesterase 1; PPT1), CLN2 (tripeptidyl peptidase 1; TPP1), and CLN10 (cathepsin D). Specific and sensitive diagnostic assays of NCLs were the main goal of this study. They are of increasing importance, particularly since enzyme replacement therapy (ERT) for NCL2 has recently become available for clinical treatment, and ERTs for further NCLs are under development. Here, we report specific and sensitive determinations for CLN1, CLN2, and CLN10 on dried blood spots by tandem mass spectrometry using multiple reaction monitoring mass spectrometry (MRM-MS). Identical substrates suitable for (i) fluorimetric determination of single enzymes and (ii) for MRM-MS determination of multiple enzymes were synthesized by chemical coupling of alkyl-umbelliferone building blocks with the corresponding peptidyl-substrate groups recognized by the target enzyme. Enzymatic determinations were performed both by fluorimetry and MRM-MS in patients with NCL1, NCL2, and NCL10 and showed good agreement in single assays. Moreover, duplex and triplex determinations were successfully performed for NCL1, NCL2, and NCL10. Specific peptidyl-(4-alkyl-umbelliferone) substrates were also synthesized for mass spectrometric determinations of different cathepsins (cathepsins-D, -F, and -B), to provide a differentiation of proteolytic specificities.

The natural history of Canavan disease: 23 new cases and comparison with patients from literature.

BACKGROUND: Canavan disease (CD, MIM # 271900) is a rare and devastating leukodystrophy of early childhood. To identify clinical features that could serve as endpoints for treatment trials, the clinical course of CD was studied retrospectively and prospectively in 23 CD patients. Results were compared with data of CD patients reported in three prior large series. Kaplan Meier survival analysis including log rank test was performed for pooled data of 82 CD patients (study cohort and literature patients). RESULTS: Onset of symptoms was between 0 and 6 months. Psychomotor development of patients was limited to abilities that are usually gained within the first year of life. Macrocephaly became apparent between 4 and 18 months of age. Seizure frequency was highest towards the end of the first decade. Ethnic background was more diverse than in studies previously reported. A CD severity score with assessment of 11 symptoms and abilities was developed. CONCLUSIONS: Early hallmarks of CD are severe psychomotor disability and macrocephaly that develop within the first 18 months of life. While rare in the first year of life, seizures increase in frequency over time in most patients. CD occurs more frequently outside Ashkenazi Jewish communities than previously reported. Concordance of phenotypes between siblings but not patients with identical ASPA mutations suggest the influence of yet unknown modifiers. A CD severity score may allow for assessment of CD disease severity both retrospectively and prospectively.

Genetic testing of leukodystrophies unraveling extensive heterogeneity in a large cohort and report of five common diseases and 38 novel variants.

This study evaluates the genetic spectrum of leukodystrophies and leukoencephalopathies in Iran. 152 children, aged from 1 day to 15 years, were genetically tested for leukodystrophies and leukoencephalopathies based on clinical and neuroradiological findings from 2016 to 2019. Patients with a suggestive specific leukodystrophy, e. g. metachromatic leukodystrophy, Canavan disease, Tay-Sachs disease were tested for mutations in single genes (108; 71%) while patients with less suggestive findings were evaluated by NGS. 108 of 152(71%) had MRI patterns and clinical findings suggestive of a known leukodystrophy. In total, 114(75%) affected individuals had (likely) pathogenic variants which included 38 novel variants. 35 different types of leukodystrophies and genetic leukoencephalopathies were identified. The more common identified disorders included metachromatic leukodystrophy (19 of 152; 13%), Canavan disease (12; 8%), Tay-Sachs disease (11; 7%), megalencephalic leukodystrophy with subcortical cysts (7; 5%), X-linked adrenoleukodystrophy (8; 5%), Pelizaeus-Merzbacher-like disease type 1 (8; 5%), Sandhoff disease (6; 4%), Krabbe disease (5; 3%), and vanishing white matter disease (4; 3%). Whole exome sequencing (WES) revealed 90% leukodystrophies and genetic leukoencephalopathies. The total diagnosis rate was 75%. This unique study presents a national genetic data of leukodystrophies; it may provide clues to the genetic pool of neighboring countries. Patients with clinical and neuroradiological evidence of a genetic leukoencephalopathy should undergo a genetic analysis to reach a definitive diagnosis. This will allow a diagnosis at earlier stages of the disease, reduce the burden of uncertainty and costs, and will provide the basis for genetic counseling and family planning.

Retention of lysosomal protein CLN5 in the endoplasmic reticulum causes neuronal ceroid lipofuscinosis in Asian sibship.

The neuronal ceroid lipofuscinoses (NCLs) form a group of autosomal recessively inherited neurodegenerative disorders that mainly affect children. Ten NCL forms can be distinguished by age at onset, clinicopathologic features, and genetics. In eight of these forms, the underlying genes have been identified. At present, approximately 10% of all patients do not fall into one of the eight known genetic forms of NCL. We have identified two Asian families with two novel homozygous mutations in the CLN5 gene. In the first Pakistani family, two children developed symptoms of an early juvenile NCL. After exclusion of mutations in genes known to be associated with this age of onset in families from many different countries (CLN1, CLN2, CLN3, CLN6, CLN8 and CLN10) SNP array-based homozygosity mapping led to the identification of a novel homozygous mutation c.1072_1073delTT (p.Leu358AlafsX4) in CLN5. In the second Afghan family, two children developed symptoms of a late infantile NCL. The mutation c.1137G>T (p.Trp379Cys) in CLN5 was identified. The affected children in these families represent the first reported CLN5 patients originating in Asian sibships. Expression analysis showed that mutant p.Leu358AlafsX4 CLN5 is truncated and lacks a used N-glycosylation site at Asn401. The missense mutation p.Trp379Cys affected neither the size nor glycosylation of the CLN5 protein. Double immunofluorescence microscopy showed that while the wild-type CLN5 protein is localized in lysosomes, both mutant CLN5 proteins are retained in the endoplasmic reticulum rather than reaching the lysosome.