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.

An Adapted Clinical Measurement Tool for the Key Symptoms of CLN2 Disease

Abstract Neuronal ceroid lipofuscinosis type-2 (CLN2) disease is a rare, autosomalrecessive,pediatric-onset,neurodegenerative lysosomal storage disease caused by mutations in the TPP1 gene. Cerliponase alfa (Brineura®), a recombinant form of human tripeptidyl peptidase-1, was recently developed as a treatment for CLN2 disease. In clinical trials, the primary end point to evaluate treatment effect was the aggregate score for the motor and language (ML) domains of the CLN2 Clinical Rating Scale, an adaptation of the Hamburg scale's component items that include anchor point definitions to allow consistent ratings in multinational, multisite, clinical efficacy studies. Psychometric analyses demonstrated that the ML score of the CLN2 Clinical Rating Scale and individual item scores are well defined and possess adequate measurement properties (reliability, validity, and responsiveness) to demonstrate a clinical benefit over time. Additionally, analyses comparing the CLN2 Clinical Rating Scale ML ratings to the Hamburg scale's ML ratings demonstrated adequate similarity.

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.

Long-term Outcome of Allogeneic Hematopoietic Stem Cell Transplantation in Patients With Juvenile Metachromatic Leukodystrophy Compared With Nontransplanted Control Patients.

IMPORTANCE: Allogeneic hematopoietic stem cell transplantation (HSCT) has been the only treatment option clinically available during the last 20 years for juvenile metachromatic leukodystrophy (MLD), reported with variable outcome and without comparison with the natural course of the disease. OBJECTIVE: To compare the long-term outcome of patients who underwent allogeneic HSCT with control patients who did not among a cohort with juvenile MLD. DESIGN, SETTING, AND PARTICIPANTS: Patients with juvenile MLD born between 1975 and 2009 and who received HSCT at a median age of 7 years (age range, 1.5-18.2 years) and nontransplanted patients with juvenile MLD born between 1967 and 2007 were included in this case-control study. The median follow-up after HSCT was 7.5 years (range, 3.0-19.7 years). Patients underwent HSCT at 3 German centers between 1991 and 2012. The analysis was done between July 2014 and August 2015. MAIN OUTCOMES AND MEASURES: Survival and transplantation-related mortality, loss of gross motor function (Gross Motor Function Classification in MLD), loss of any language function, and magnetic resonance imaging (MRI) severity score for cerebral changes. To explore prognostic factors at baseline, patients who underwent HSCT (hereafter, transplanted patients) were a priori divided into stable vs progressive disease, according to gross motor and cognitive function. RESULTS: Participants were 24 transplanted patients (11 boys, 13 girls) and 41 control patients (22 boys, 19 girls) who did not receive transplantation (hereafter, nontransplanted patients) with juvenile MLD. Among the transplanted patients, 4 children died of transplantation-related mortality, and 2 additional children died of rapid MLD progression 1.5 and 8.6 years after HSCT, resulting in a 5-year survival of 79% (19 of 24). Among the nontransplanted patients, 5-year survival after disease onset was 100% (41 of 41). However, 11 died of MLD progression, resulting in similar overall survival within the observation period. Nine of the long-term survivors after HSCT had disease progression, while 11 showed stable disease. Compared with the nontransplanted patients, the transplanted patients were less likely to lose their gross motor or language function and demonstrated significantly lower MRI severity scores at the latest examination. Patients after HSCT were more likely to have a stable disease course when undergoing HSCT at an early stage with no or only mild gross motor deficits (Gross Motor Function Classification in MLD level 0 or 1) and an IQ of at least 85, when age at disease onset was older than 4 years, or when MRI severity scores were low (preferably ≤17). CONCLUSIONS AND RELEVANCE: Among patients with juvenile MLD, patients who underwent HSCT had a better gross motor and language outcome and lower MRI severity scores compared with nontransplanted patients. Transplantation at a presymptomatic or early symptomatic stage of juvenile MLD is associated with a reasonable chance for disease stabilization.

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.

Brain iron quantification by MRI in mitochondrial membrane protein-associated neurodegeneration under iron-chelating therapy.

Therapeutic trials for Neurodegeneration with Brain Iron Accumulation have aimed at a reduction of cerebral iron content. A 13-year-old girl with mitochondrial membrane protein-associated neurodegeneration treated with an iron-chelating agent was monitored by R2 relaxometry, R2* relaxometry, and quantitative susceptibility mapping to estimate the brain iron content. The highly increased brain iron content slowly decreased in the substantia nigra but remained stable for globus pallidus. The estimated iron content was higher by R2* compared to R2 and quantitative susceptibility mapping, a finding not previously observed in the brain of healthy volunteers. A hypothesis explaining this discrepancy is offered.

Lysosomal leukodystrophies: Krabbe disease and metachromatic leukodystrophy.

Genetic deficiencies of lysosomal catabolic pathways lead to storage disorders with multiple organ abnormalities or to degeneration of purely nervous structures. Krabbe disease and metachromatic leukodystrophy are caused by metabolic errors concerning lipids of neural membranes. They are characterized by demyelination of the central nervous system and, variably, the peripheral nerves. Their clinical presentation is a relentlessly progressive motor and mental deterioration starting at any age between infancy and adolescence. MRI demonstrates characteristic lesions of brain white matter. In Krabbe disease, deficient galactocerebroside ß-galactosidase activity causes accumulation of lipids in "globoid" macrophages and of psychosine, which is toxic to oligodendrocytes. Diagnosis depends on demonstration of the enzyme deficiency. Experimental treatment is limited to hematopoietic stem cell transplantation, which can favorably alter the course of disease in certain situations. In metachromatic leukodystrophy, deficient activity of arylsulfatase A, or lack of a cofactor, causes accumulation of sulfatide in various tissues and diffuse demyelination. Symptoms are neurological, but gallbladder dysfunction may be present. Diagnosis depends on demonstrating the enzyme deficiency and elevated urinary sulfatide. In a rare variant, multiple sulfatases are deficient. Stem cell transplantation may prevent disease progression in selected cases. Enzyme replacement is being evaluated, and gene therapies are being developed.

RNASET2-deficient cystic leukoencephalopathy resembles congenital cytomegalovirus brain infection.

Congenital cytomegalovirus brain infection without symptoms at birth can cause a static encephalopathy with characteristic patterns of brain abnormalities. Here we show that loss-of-function mutations in the gene encoding the RNASET2 glycoprotein lead to cystic leukoencephalopathy, an autosomal recessive disorder with an indistinguishable clinical and neuroradiological phenotype. Congenital cytomegalovirus infection and RNASET2 deficiency may both interfere with brain development and myelination through angiogenesis or RNA metabolism.

Stabilization of juvenile metachromatic leukodystrophy after bone marrow transplantation: a 13-year follow-up.

A 29-year-old female patient with juvenile metachromatic leukodystrophy diagnosed at age 14 years received a bone marrow transplant at age 16 years. A report was published 6 years after bone marrow transplantation concluding that the disease had slowly progressed in the 2 years following bone marrow transplantation. We now report on a further 7-year follow-up, typified by a steady state of spastic paraplegia and mild dementia. Neurophysiological, neuroradiological, and psychological status also remained stable. In the patient's leukocytes, the activity of arylsulfatase A, the enzyme deficient in untreated metachromatic leukodystrophy, was within the normal range whereas urinary sulfatides remained elevated. Data on the natural course of juvenile metachromatic leukodystrophy are rare, so in the present case it is difficult to establish whether the rather favorable course can be attributed with certainty to bone marrow transplantation. The long-term stabilization in this patient, however, suggested that bone marrow transplantation may halt the progression of juvenile metachromatic leukodystrophy.

Defective endoplasmic reticulum-resident membrane protein CLN6 affects lysosomal degradation of endocytosed arylsulfatase A.

Variant late infantile neuronal ceroid lipofuscinosis, a lysosomal storage disorder characterized by progressive mental deterioration and blindness, is caused by mutations in a polytopic membrane protein (CLN6) with unknown intracellular localization and function. In this study, transient transfection of BHK21 cells with CLN6 cDNA and immunoblot analysis using peptide-specific CLN6 antibodies demonstrated the expression of a approximately 27-kDa protein that does not undergo proteolytic processing. Cross-linking experiments revealed the presence of CLN6 dimers. Using double immunofluorescence microscopy, epitope-tagged CLN6 was shown to be retained in the endoplasmic reticulum (ER) with no colocalization with the cis-Golgi or lysosomal markers. The translocation into the ER and proper folding were confirmed by the N-linked glycosylation of a mutant CLN6 polypeptide. Pulse-chase labeling of fibroblasts from CLN6 patients and from sheep (OCL6) and mouse (nclf) models of the disease followed by immunoprecipitation of cathepsin D indicated that neither the synthesis, sorting nor the proteolytic processing of this lysosomal enzyme was affected in CLN6-defective cells. However, the degradation of the endocytosed index protein arylsulfatase A was strongly reduced in all of the mutant CLN6 cell lines compared with controls. These data suggest that defects in the ER-resident CLN6 protein lead to lysosomal dysfunctions, which may result in lysosomal accumulation of storage material.

Mutation of the glycosylated asparagine residue 286 in human CLN2 protein results in loss of enzymatic activity.

Late infantile neuronal ceroid lipofuscinosis (LINCL) is caused by the deficiency of the lysosomal tripeptidyl peptidase-I encoded by CLN2. We previously detected in two LINCL patients a homozygous missense mutation, p.Asn286Ser, that affects a potential N-glycosylation site. We introduced the p.Asn286Ser mutation into the wild-type CLN2 cDNA and performed transient expression analysis to determine the effect on the catalytic activity, intracellular targeting, and glycosylation of the CLN2 protein. Expression of mutant p.Asn286Ser CLN2 in HEK293 cells revealed that the mutant was enzymatically inactive. Western blot analysis demonstrated that at steady state the amounts of expressed p.Asn286Ser CLN2 were reduced compared with wild-type expressing cells. The rate of synthesis and the sorting of the newly synthesized p.Asn286Ser CLN2 in the Golgi was not affected compared with wild-type CLN2 protein. The electrophoretic mobility of the immunoprecipitated mutant p.Asn286Ser CLN2 was increased by approximately 2 kDa compared with the wild-type CLN2 protein, whereas deglycosylation led to the generation of polypeptides of the same apparent size. The data suggest that mutant p.Asn286Ser CLN2 lacks one oligosaccharide chain resulting in enzymatic inactivation.

Sequence diversity of KIAA0027/MLC1: are megalencephalic leukoencephalopathy and schizophrenia allelic disorders?

The aim of the study is to validate the etiological role of KIAA0027/MLC1 in childhood-onset megalencephalic leukoencephalopathy with subcortical cysts (MLC) and in schizophrenia, particularly the catatonic subtype, which were reported to be allelic diseases. Among a series of five patients with MLC, four mutant alleles were detected: one case of compound heterozygosity for a splice site mutation and a six-base-pair in-frame deletion, one patient with a homozygous frameshifting insertion-deletion, and a further case heterozygous for a A157E substitution. A systematic mutation screening in 140 index cases with schizophrenia revealed 13 different single nucleotide polymorphisms (SNPs): one SNP in the 5'-UTR, seven SNPs in intronic regions, two synonymous codon variants (T52, Y199), and three coding variants. Two of them, C171F and N218K, were observed in controls at a significant frequency. The L309M variant that was previously supposed to be the causative factor for chromosome 22q(tel) linked-periodic catatonia was found nonsegregating in a further multiplex pedigree. Furthermore, a complicated 33-bp insertion/deletion polymorphism at the 5'-end of exon 11 of MLC1 was found at equal frequency among schizophrenic patients and controls. In summary, our study provides further evidence for allelic heterogeneity in megalencephalic leukoencephalopathy, excludes MLC1 as a susceptibility locus for schizophrenia, and thereby rules out that MLC and schizophrenia are allelic disorders.

Plasma antioxidants in pediatric patients with glycogen storage disease, diabetes mellitus, and hypercholesterolemia.

Oxidative modification of lipoproteins in vessel walls plays a key role in atherogenesis. Patients with glycogen storage disease type Ia (GSD Ia) do not develop premature atherosclerosis despite severe hyperlipidemia. We analyzed antioxidative defense and oxidative stress in plasma and serum of patients with GSD Ia (n = 17) compared to patients with type I diabetes mellitus (DMI, n = 17), familial hypercholesterolemia (FH, n = 18), and healthy controls (n = 20). We measured the total radical-trapping antioxidant parameter (TRAP), single antioxidants (sulfhydryl groups, uric acid, vitamin C, alpha-tocopherol, coenzyme Q10), malondialdehyde, oxidized low density lipoprotein (LDL) antibodies, lipid profile [cholesterol, triglyceride, lipoprotein (a)], homocysteine, and hemoglobin (Hb)A(1C). TRAP levels were elevated in the GSD Ia group (p <.01) and correlated with elevated uric acid levels (r = 0.72, p =.001). None of the other plasma antioxidants correlated with TRAP levels. DMI patients showed decreased sulfhydryl groups (p <.01) and a reduced ubiquinol-10 fraction (p <.01). Malondialdehyde (p <.001) and oxidized LDL autoantibodies (p <.05) were increased in the diabetic group. In FH patients, parameters of oxidative stress and TRAP did not differ from controls. We conclude that in GSD Ia an increased antioxidative defense in plasma may protect against lipid peroxidation and thus against premature atherosclerosis. Furthermore, we demonstrated that in DMI increased oxidative mechanisms are already present in childhood.