Spectrum of Leukodystrophy and Genetic Leukoencephalopathy in Indian Population Diagnosed by Clinical Exome Sequencing and Clinical Utility

Background and Objectives

Next-generation sequencing (NGS) has expedited the diagnostic process and unearthed many rare disorders in leukodystrophy (LD) and genetic leukoencephalopathy (gLE). Despite the progress in genomics, there is a paucity of data on the distribution of genetic white matter disorders (WMDs) and the diagnostic utility of NGS-based assays in a clinical setting. This study was initiated to explore the clinical, radiologic, and genetic spectrum of LD and gLE in the Indian population and also to estimate the diagnostic yield of clinical exome sequencing (CES).

Methods

This is a retrospective descriptive analysis of patients with a diagnosis of genetic WMDs from a single tertiary referral center who had CES performed as part of the diagnostic evaluation between January 2016 and December 2021. The demographic, clinical, radiologic, and genetic data were collected. The variants were classified using the American College of Medical Genetics and Genomics criteria. Pathogenic and likely pathogenic variants were included in the calculation of the diagnostic yield.

Results

In the study period, 138 patients were clinically diagnosed with either LD or gLE, of which 86 patients underwent CES. Pathogenic variants, likely pathogenic variants, and variants of uncertain significance with phenotype match were seen in 40 (41.8%), 13 (29.1%), and 15 (15.2%) patients, respectively. The mean age at onset in these 68 patients was 6.35 years (range 1 month-39 years), and 38 (55.9%) were male. LDs and gLE were diagnosed in 31 and 37 patients, respectively. 56 patients (71.8%) had autosomal recessive inheritance. The common clinical presentations were developmental delay (23.5%), psychomotor regression (20.6%), progressive myoclonic epilepsy syndrome (19.1%), and spastic ataxia (14.7%). Myelin disorders (48.5%) and leuko-axonopathies (41.2%) were the commonest type of disorders. The most frequently identified genes were ARSA, CLN5, ABCD1, CLN6, TPP1, HEXA, and L2HGDH. The diagnostic yield of the study was 61.6% (53/86), which increased to 79.1% when VUS with phenotype match were included.

Discussion

This study demonstrated a high diagnostic yield from proband-only CES in the evaluation of genetic WMDs and should be considered as a first-line investigation for genetic diagnosis.

Classification of Evidence

This study provides Class IV evidence that proband-only clinical exome sequencing is a useful "first-line investigation" for patients with genetic white matter disorders.

Overview of Neuro-Ophthalmic Findings in Leukodystrophies

Background: Leukodystrophies are a group of rare genetic diseases that primarily affect the white matter of the central nervous system. The broad spectrum of metabolic and pathological causes leads to manifestations at any age, most often in childhood and adolescence, and a variety of symptoms. Leukodystrophies are usually progressive, resulting in severe disabilities and premature death. Progressive visual impairment is a common symptom. Currently, no overview of the manifold neuro-ophthalmologic manifestations and visual impact of leukodystrophies exists. Methods: Data from 217 patients in the Hamburg leukodystrophy cohort were analyzed retrospectively for neuro-ophthalmologic manifestations, age of disease onset, and magnetic resonance imaging, visual evoked potential, and optical coherence tomography findings and were compared with data from the literature. Results: In total, 68% of the patients suffered from neuro-ophthalmologic symptoms, such as optic atrophy, visual neglect, strabismus, and nystagmus. Depending on the type of leukodystrophy, neuro-ophthalmologic symptoms occurred early or late during the course of the disease. Magnetic resonance imaging scans revealed pathologic alterations in the visual tract that were temporally correlated with symptoms. Conclusions: The first optical coherence tomography findings in Krabbe disease and metachromatic leukodystrophy allow retinal assessments. Comprehensive literature research supports the results of this first overview of neuro-ophthalmologic findings in leukodystrophies.

Approaches to diagnosis for individuals with a suspected inherited white matter disorder

Leukodystrophies are heritable disorders with white matter abnormalities observed on central nervous system magnetic resonance imaging. Pediatric leukodystrophies have long been known for their classically high, "unsolved" rate. Indeed, these disorders provide a diagnostic dilemma for many clinicians as over 100 genetic disorders alone may present with white matter abnormalities, with this figure not taking into account the substantial number of infectious agents, toxicities, and acquired disorders that may affect the white matter of the brain. Achieving a diagnosis may be the single most important step in the clinical course of a leukodystrophy-affected individual, with important implications for care and quality of life. For certain disorders, prompt recognition can direct therapeutic intervention with significant implications and requires urgent recognition. In this review, we cover newborn screening efforts, standard-of-care testing methodologies, and next generation sequencing approaches that continue to change the landscape of leukodystrophy diagnosis. Early studies have shown that next generation sequencing approaches, particularly exome and now genome sequencing have proven to be powerful in helping resolve many cases that were refractory to a single gene or linkage analysis approach. In addition, other methods are required for cases that remain persistently unsolved after next generation sequencing methods have been used. In the past more than half of affected individuals never achieved an etiologic diagnosis, and when they did, the reported times to diagnosis were >5 years although molecular testing has allowed this to be reduced to closer to 16 months. For affected families, next generation sequencing technologies have finally provided a way to fill gaps in diagnosis.

A Rare Case of Hypomyelinating Leukodystrophy and Its Management: A Case Report and Literature Review

A subset of hereditary white matter disorders called hypomyelinating leukodystrophies (HLD) is characterized primarily by the absence of myelin deposition. Although the clinical presentation can be mild and the development of symptoms can occur in adolescence or adulthood, the majority of severe cases present during infancy and early childhood with significant neurological impairments. The clinical features vary from muscle stiffness to seizures and developmental delay. The detailed myelination process can be seen with magnetic resonance imaging (MRI), and many patients are diagnosed using MRI pattern recognition and next-generation sequencing (NGS) in most cases. Here, we report a case of an infant suffering from the hypomyelinating leukodystrophy-13 (HLD-13) variant, whose next-generation sequencing revealed a pathogenic homozygous variant.

Pulmonological issues

Pediatric leukodystrophies are rare neurodegenerative diseases involving multiple systems. Each form has unique neurologic features but are characterized by encephalopathy with accompanying impairments evidenced in reflexes, muscle tone and movement control. Weakness of expiratory, inspiratory, and upper airway muscles may lead to impaired airway secretion clearance resulting in recurrent respiratory infections, dysphagia, sleep-disordered breathing, restrictive lung disease, and ultimately chronic respiratory insufficiency.

Echoes of William Gowers's concept of abiotrophy

Among William Gowers's many contributions to neurology, the concept of abiotrophy ("an essential failure of vitality") has been relatively overlooked. In this article, we review the echoes of Gowers's concept in neurology, ophthalmology, and aging research. We also argue that abiotrophy is broader than both heredodegeneration and neurodegeneration. Unlike the common view that it simply means premature aging, abiotrophy currently can be understood as a progressive degenerative process of a mature specialized tissue, which is nonsynchronous with normal aging and may affect organs or systems early in life, resulting from the age-dependent effects of genetic mutations or variants, even if environmental factors may also causally contribute to the process. Although the term has largely fallen out of use, there are likely to be everlasting echoes of Gowers's concept, through which he is to be considered a source of the modern thinking about the etiology and nosology of neurological diseases.

Metronidazole-Induced Encephalopathy in a 16-Year-Old Girl with Crohn’s Disease: Case Report and Review of the Pediatric Literature

Metronidazole-induced encephalopathy (MIE) is a rare and unpredictable complication that is most commonly reported in adults. Here, we present the case of MIE in a patient treated with rectal, oral, and intravenous metronidazole. This is the first case of MIE reported after suppositories. A 16-year-old girl with Crohn’s disease treated with mesalazine and exclusive enteral nutrition was operated on due to perianal fistulas and abscesses. She received oral metronidazole for 25 days and rectal metronidazole for 15 days as an adjuvant before surgery. Moreover, 2.5 g of intravenous metronidazole was administrated during the perioperative period. The second day after the surgery, symptoms of cerebellar syndrome appeared. She presented with an inability to coordinate balance and gait. Although she showed accurate verbal responses, her speech was slow, slurred, and scanning. The finger–nose test was positive. The T2-weighted magnetic resonance imaging revealed an increased symmetrical signal within the dentate nuclei of the cerebellum and in the corpus callosum. The changes were characterized by restricted diffusion. Based on the clinical picture and magnetic resonance imaging findings, MIE was diagnosed. Treatment with metronidazole was discontinued. The cumulative dose of metronidazole that she received for 29 days was 54 g: 38 g p.o., 13.5 g p.r., and 2.5 g i,v. The first symptoms appeared on the 28th day of antibiotic therapy after receiving 52 g of metronidazole. The neurological symptoms resolved after six days; however, three days after the resolution, paresthesia appeared in the distal phalanges of both feet and lasted for approximately two months. Our report highlights that neurologic symptoms related to metronidazole treatment should raise the suspicion of MIE.

Blood-brain barrier delivery for lysosomal storage disorders with IgG-lysosomal enzyme fusion proteins

The majority of lysosomal storage diseases affect the brain. Treatment of the brain with intravenous enzyme replacement therapy is not successful, because the recombinant lysosomal enzymes do not cross the blood-brain barrier (BBB). Biologic drugs, including lysosomal enzymes, can be re-engineered for BBB delivery as IgG-enzyme fusion proteins. The IgG domain of the fusion protein is a monoclonal antibody directed against an endogenous receptor-mediated transporter at the BBB, such as the insulin receptor or the transferrin receptor. This receptor transports the IgG across the BBB, in parallel with the endogenous receptor ligand, and the IgG acts as a molecular Trojan horse to ferry into brain the lysosomal enzyme genetically fused to the IgG. The IgG-enzyme fusion protein is bi-functional and retains both high affinity binding for the BBB receptor, and high lysosomal enzyme activity. IgG-lysosomal enzymes are presently in clinical trials for treatment of the brain in Mucopolysaccharidosis.

Baicalin Promotes CNS Remyelination via PPARγ Signal Pathway

Background and Objectives

Demyelinating diseases in the CNS are characterized by myelin sheath destruction or formation disorder that leads to severe neurologic dysfunction. Remission of such diseases is largely dependent on the differentiation of oligodendrocytes precursor cells (OPCs) into mature myelin-forming OLGs at the demyelinated lesions, which is defined as remyelination. We discover that baicalin (BA), a natural flavonoid, in addition to its well-known antiinflammatory effects, directly stimulates OLG maturation and CNS myelin repair.

Methods

To investigate the function of BA on CNS remyelination, we develop the complementary in vivo and in vitro models, including physiologic neonatal mouse CNS myelinogenesis model, pathologic cuprizone-induced (CPZ-induced) toxic demyelination model, and postnatal OLG maturation assay. Furthermore, molecular docking, pharmacologic regulation, and transgenic heterozygous mice were used to clarify the target and action of the mechanism of BA on myelin repair promotion.

Results

Administration of BA was not only merely effectively enhanced CNS myelinogenesis during postnatal development but also promoted remyelination and reversed the coordination movement disorder in the CPZ-induced toxic demyelination model. Of note, myelin-promoting effects of BA on myelination or regeneration is peroxisome proliferator-activated receptor γ (PPARγ) signaling-dependent.

Discussion

Our work demonstrated that BA promotes myelin production and regeneration by activating the PPARγ signal pathway and also confirmed that BA is an effective natural product for the treatment of demyelinating diseases.

Hypomyelination and Congenital Cataract: Clinical, Imaging, and Genetic Findings in Three Tunisian Families and Literature Review

Hypomyelination and congenital cataract (HCC) is characterized by congenital cataract, progressive neurologic impairment, and diffuse myelin deficiency. This autosomal recessive disorder is caused by homozygous variant in the FAM126A gene. Five consanguineous Tunisian patients, belonging to three unrelated families, underwent routine blood tests, electroneuromyography, and magnetic resonance imaging of the brain. The direct sequencing of FAM126A exons was performed for the patients and their relatives. We summarized the 30 previously published HCC cases. All of our patients were carriers of a previously reported c.414 + 1G > T (IVS5 + 1G > T) variant, but the clinical spectrum was variable. Despite the absence of a phenotype-genotype correlation in HCC disease, screening of this splice site variant should be performed in family members at risk.

Death rates in the U.S. due to Leukodystrophies with pediatric forms

To use national mortality and state death certificate records to estimate disease specific mortality rates among pediatric and adult populations for 23 leukodystrophies (LDs) with pediatric forms. Additionally, to calculate yearly prevalence and caseload of the most severe LD cases that will eventually result in pediatric death (i.e., pediatric fatality cases). Death certificate records describing cause of death were collected from states based on 10 ICD-10 codes associated with the 23 LDs. Deaths in the U.S. with these codes were distributed into categories based on proportions identified in state death certificate data. Mortality rates, prevalence, and caseload were calculated from resulting expected numbers, population sizes, and average lifetimes. An estimated 1.513 per 1,000,000 0-17 year old's died of these LDs at average age 5.2 years and 0.194 for those ≥18 at an average age of 42.3 years. Prevalence of pediatric fatality cases of these LDs declined from 1999 through 2007 and then remained constant at 6.2 per million children per year through 2012. Epidemiological information, currently lacking for rare diseases, is useful to newborn screening programs, research funding agencies, and care centers for LD patients. Methods used here are generally useful for studying rare diseases.

Biallelic mutations in RNF220 cause laminopathies featuring leukodystrophy, ataxia and deafness

Leukodystrophies are a heterogeneous group of rare inherited disorders that involve preferentially the white matter of the central nervous system (CNS). These conditions are characterized by a primary glial cell and myelin sheath pathology of variable etiology, which causes secondary axonal degeneration, generally emerging with disease progression. Whole exome sequencing performed in 5 large consanguineous nuclear families allowed to identify homozygosity for two recurrent missense variants affecting highly conserved residues of RNF220 as the causative event underlying a novel form of leukodystrophy with ataxia and sensorineural deafness. We report on two homozygous missense variants (p.R363Q and p.R365Q) in the ubiquitin E3 ligase RNF220 as the cause underlying a novel form of leukodystrophy with ataxia and sensorineural deafness having fibrotic cardiomyopathy and hepatopathy as associated features, in seven consanguineous families. Mass spectrometry analysis identified lamin B1 as RNF220 binding protein and co-immunoprecipitation experiments demonstrated reduced binding of both RNF220 mutants to lamin B1. We demonstrate that RNF220 silencing in Drosophila melanogaster specifically affects proper localization of lamin Dm0, the fly lamin B1 orthologue, promotes its aggregation, and causes a neurodegenerative phenotype, strongly supporting the functional link between RNF220 and lamin B1. Finally, we demonstrate that RNF220 plays a crucial role in the maintenance of nuclear morphology: mutations primary skin fibroblasts determine nuclear abnormalities such as blebs, herniations and invaginations, which are typically observed in cells of patients affected by laminopathies. Overall, our data identify RNF220 as a gene implicated in leukodystrophy with ataxia and sensorineural deafness, and document a critical role of RNF220 in the regulation of nuclear lamina. Our findings provide further evidence on the direct link between nuclear lamina dysfunction and neurodegeneration.

Hereditary Myelopathies

Hereditary myelopathies are an important and likely underappreciated component of neurogenetic disease. While previously distinctions have been made by age of onset, the growing power and availability of high-quality neuroimaging and next-generation sequencing are increasingly expanding classical phenotypes and diminishing the utility of age-based classifications. Increasingly, cases of "atypical" disease presentations are challenging past assumptions regarding the age of onset and survival in many disorders and identifying allelic syndromes in others. Despite this, there is poor awareness of the potential for spinal involvement in many diseases that typically affect the brain. Broadly speaking, congenital myelopathies can be neuroanatomically grouped into motor neuron, axonopathy, spinocerebellar, cerebroleukodystrophy, and pan-neuraxis (generally central nervous system predominant with associated axonopathy) disorders.Here, we review hereditary causes of myelopathy, organized by neuroanatomy, and highlight atypical presentations. We discuss findings concerning an underlying genetic etiology for myelopathy, as well as practical, technical, and ethical considerations of diagnostic genetic testing.

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.

Novel disease-causing variants in a cohort of Iranian patients with metachromatic leukodystrophy and in silico analysis of their pathogenicity

OBJECTIVE

Metachromatic leukodystrophy (MLD) is an autosomal recessive leukodystrophy caused by deficiency of aryl sulfatase A (ASA) activity affecting the nervous system. MLD and mutations in ARSA have not been widely studied in non-European cohorts. The genotype-phenotype spectrum of MLD patients was investigated in this study of a cohort of Iranian leukodystrophy patients. In silico analysis was performed to investigate the pathogenicity of the variants.

METHODS

Genetic analysis for 25 patients was performed with direct sequencing of the ARSA gene. The missense variants underwent in silico analysis to characterize the pathogenicity based on predicted structural and stability changes.

RESULTS

19 patients had variants in ARSA genes, including 18 homozygotes and one compound heterozygote individual. In 6 individuals no mutations were found in ARSA gene, suggesting an alternative cause of their leukodystrophy. We found 5 novel disease causing variants: p.Phe64Ile, p.Ser292Alafs*34, p.Arg99Profs*35, p.Phe400Leu and p.Leu429Pro. 32 % of the patients had p.Gly311Ser substitution and resulted in juvenile MLD type. Different in silico analysis showed variable pathogenic effect for the variants.

CONCLUSION

c.931 G > A (p.Gly311Ser) and c.465 + 1 G > A variants are the most frequent alleles among Iranian MLD patients and five mutations appear to be confined to the Iranian patients. Population screening for these variants may be helpful to reduce the burden of the disease in this part of the world.

Glial cells in the driver seat of leukodystrophy pathogenesis

Glia cells are often viewed as support cells in the central nervous system, but recent discoveries highlight their importance in physiological functions and in neurological diseases. Central to this are leukodystrophies, a group of progressive, neurogenetic disease affecting white matter pathology. In this review, we take a closer look at multiple leukodystrophies, classified based on the primary glial cell type that is affected. While white matter diseases involve oligodendrocyte and myelin loss, we discuss how astrocytes and microglia are affected and impinge on oligodendrocyte, myelin and axonal pathology. We provide an overview of the leukodystrophies covering their hallmark features, clinical phenotypes, diverse molecular pathways, and potential therapeutics for clinical trials. Glial cells are gaining momentum as cellular therapeutic targets for treatment of demyelinating diseases such as leukodystrophies, currently with no treatment options. Here, we bring the much needed attention to role of glia in leukodystrophies, an integral step towards furthering disease comprehension, understanding mechanisms and developing future therapeutics.

Neurogenic Bladder and Acute Kidney Injury in Leukodystrophy

Leukodystrophies are genetic white matter disorders. In the young, they represent an important cause of progressive neurological disability. Impairment of the bladder function may be part of the clinical picture of leukodystrophies. A neurogenic bladder is a dysfunctional urinary bladder caused by a disease of the central or peripheral nervous system involved in the control of micturition. In our patient, leukodystrophy-induced neurogenic bladder and acute kidney injury were revealed. If untreated, a neurogenic bladder can cause renal failure and urinary incontinence. Patients with a neurogenic bladder should be monitored, and management should aim to preserve renal function and achieve social continence.

An update on clinical, pathological, diagnostic, and therapeutic perspectives of childhood leukodystrophies

Introduction: Leukodystrophies constitute heterogenous group of rare heritable disorders primarily affecting the white matter of central nervous system. These conditions are often under-appreciated among physicians. The first clinical manifestations of leukodystrophies are often nonspecific and can occur in different ages from neonatal to late adulthood periods. The diagnosis is, therefore, challenging in most cases.Area covered: Herein, the authors discuss different aspects of leukodystrophies. The authors used MEDLINE, EMBASE, and GOOGLE SCHOLAR to provide an extensive update about epidemiology, classifications, pathology, clinical findings, diagnostic tools, and treatments of leukodystrophies. Comprehensive evaluation of clinical findings, brain magnetic resonance imaging, and genetic studies play the key roles in the early diagnosis of individuals with leukodystrophies. No cure is available for most heritable white matter disorders but symptomatic treatments can significantly decrease the burden of events. New genetic methods and stem cell transplantation are also under investigation to further increase the quality and duration of life in affected population.Expert opinion: The improvements in molecular diagnostic tools allow us to identify the meticulous underlying etiology of leukodystrophies and result in higher diagnostic rates, new classifications of leukodystrophies based on genetic information, and replacement of symptomatic managements with more specific targeted therapies.Abbreviations: 4H: Hypomyelination, hypogonadotropic hypogonadism and hypodontia; AAV: Adeno-associated virus; AD: autosomal dominant; AGS: Aicardi-Goutieres syndrome; ALSP: Axonal spheroids and pigmented glia; APGBD: Adult polyglucosan body disease; AR: autosomal recessive; ASO: Antisense oligonucleotide therapy; AxD: Alexander disease; BAEP: Brainstem auditory evoked potentials; CAA: Cerebral amyloid angiopathy; CADASIL: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy; CARASAL: Cathepsin A-related arteriopathy with strokes and leukoencephalopathy; CARASIL: Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy; CGH: Comparative genomic hybridization; ClC2: Chloride Ion Channel 2; CMTX: Charcot-Marie-Tooth disease, X-linked; CMV: Cytomegalovirus; CNS: central nervous system; CRISP/Cas9: Clustered regularly interspaced short palindromic repeat/CRISPR-associated 9; gRNA: Guide RNA; CTX: Cerebrotendinous xanthomatosis; DNA: Deoxyribonucleic acid; DSB: Double strand breaks; DTI: Diffusion tensor imaging; FLAIR: Fluid attenuated inversion recovery; GAN: Giant axonal neuropathy; H-ABC: Hypomyelination with atrophy of basal ganglia and cerebellum; HBSL: Hypomyelination with brainstem and spinal cord involvement and leg spasticity; HCC: Hypomyelination with congenital cataracts; HEMS: Hypomyelination of early myelinated structures; HMG CoA: Hydroxy methylglutaryl CoA; HSCT: Hematopoietic stem cell transplant; iPSC: Induced pluripotent stem cells; KSS: Kearns-Sayre syndrome; L-2-HGA: L-2-hydroxy glutaric aciduria; LBSL: Leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate; LCC: Leukoencephalopathy with calcifications and cysts; LTBL: Leukoencephalopathy with thalamus and brainstem involvement and high lactate; MELAS: Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke; MERRF: Myoclonic epilepsy with ragged red fibers; MLC: Megalencephalic leukoencephalopathy with subcortical cysts; MLD: metachromatic leukodystrophy; MRI: magnetic resonance imaging; NCL: Neuronal ceroid lipofuscinosis; NGS: Next generation sequencing; ODDD: Oculodentodigital dysplasia; PCWH: Peripheral demyelinating neuropathy-central-dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschprung disease; PMD: Pelizaeus-Merzbacher disease; PMDL: Pelizaeus-Merzbacher-like disease; RNA: Ribonucleic acid; TW: T-weighted; VWM: Vanishing white matter; WES: whole exome sequencing; WGS: whole genome sequencing; X-ALD: X-linked adrenoleukodystrophy; XLD: X-linked dominant; XLR: X-linked recessive.

Clinical and Genetic Characteristics of Leukodystrophies in Africa

Recent understanding of the genetic basis of neurological disorders in Africa has grown rapidly in the last two decades. Africa harbors the largest genetic repertoire in the world which gives unique opportunity to discover novel variant, genes, and molecular pathways associated with various neurological diseases. Despite that, large-scale genomic and exome studies are severely lacking especially for neglected diseases such as leukodystrophies. This review aims to shed light on the currently developed research in leukodystrophies in Africa. We reviewed all research articles related to “Leukodystrophy in Africa” published in Medline/PubMed and Google Scholar databases up to date. We found very few studies in leukodystrophy from Africa, especially from the Sub-Saharan regions. Metachromatic leukodystrophy was the most studied type of leukodystrophy. Published studies from North Africa (Tunisia, Morocco, and Egypt) were very limited in either sample size (case studies or single/few family studies) or molecular methods (targeted sequencing or polymerase chain reaction-restriction fragment length polymorphisms). More studies (GWAS or large family studies) with advanced techniques such as exome or whole genome sequencing are needed to unveil the genetic basis of leukodystrophy in Africa. Unmasking novel genes and molecular pathways of leukodystrophies invariably lead to better detection and treatment for both Africans and worldwide populations.

Psychiatric and Cognitive Symptoms Associated with Niemann-Pick Type C Disease: Neurobiology and Management

Niemann-Pick disease type C (NPC) is a lysosomal storage disorder that presents with a spectrum of clinical manifestations from infancy and childhood or in early or mid-adulthood. Progressive neurological symptoms including ataxia, dystonia and vertical gaze palsy are a hallmark of the disease, and psychiatric symptoms such as psychosis and mood disorders are common. These latter symptoms often present early in the course of NPC and thus these patients are often diagnosed with a major psychotic or affective disorder before neurological and cognitive signs present and the diagnosis is revised. The commonalities and characteristics of psychotic symptoms in both NPC and schizophrenia may share neuronal pathways and mechanisms and provide potential targets for research in both disorders. The neurobiology of NPC and its relationship to the pattern of neuropsychiatric and cognitive symptoms is described in this review. A number of neurobiological models are proposed as mechanisms by which NPC causes psychiatric and cognitive symptoms, informed from models proposed in schizophrenia and other metabolic disorders. There are a number of symptomatic and illness-modifying treatments for NPC currently available. The current evidence is discussed; focussing on two medications which have shown promise, miglustat and hydroxypropyl-β-cyclodextrin.

Neurodegenerative Erkrankungen des Kindesalters

Das Verständnis der neurodegenerativen Erkrankungen im Kindesalter hat sich in jüngster Zeit rasant verändert: Nicht nur die Anzahl unterschiedlicher Krankheiten und zugrunde liegender Gendefekte nimmt stetig zu, auch die Ansätze für Diagnostik und Therapie haben sich aufgrund neuerer technologischer und therapeutischer Fortschritte in dieser Krankheitsgruppe weiterentwickelt. Es wurden neue Gendefekte identifiziert, die eine Grundlage für das Verständnis der molekularen Mechanismen, die dieser Krankheitsgruppe zugrunde liegen, sowie für die Entwicklung gezielter Therapien bieten. Diese Übersichtsarbeit konzentriert sich hauptsächlich auf eine der häufigsten Krankheitsgruppen, die zu einer Degeneration des zentralen Nervensystems führen, die neuronalen Ceroid-Lipofuszinosen (NCL). Die Anzahl der NCL-verursachenden Gene und das Wissen über Genotyp-Phänotyp-Korrelationen sind in den letzten Jahren gewachsen und erste Therapien wurden entwickelt. Damit stellt diese Krankheitsgruppe die schnelle wissenschaftliche Entwicklung auf dem Gebiet der seltenen, neurodegenerativen Erkrankungen im Kindesalter sehr gut dar.

Adulthood leukodystrophies

The leukodystrophies are a group of inherited white matter disorders with a heterogeneous genetic background, considerable phenotypic variability and disease onset at all ages. This Review focuses on leukodystrophies with major prevalence or primary onset in adulthood. We summarize 20 leukodystrophies with adult presentations, providing information on the underlying genetic mutations and on biochemical assays that aid diagnosis, where available. Definitions, clinical characteristics, age of onset, MRI findings and treatment options are all described, providing a comprehensive overview of the current knowledge of the various adulthood leukodystrophies. We highlight the distinction between adult-onset leukodystrophies and other inherited disorders with white matter involvement, and we propose a diagnostic pathway for timely recognition of adulthood leukodystrophies in a routine clinical setting. In addition, we provide detailed clinical information on selected adult-onset leukodystrophies, including X-linked adrenoleukodystrophy, metachromatic leukodystrophy, cerebrotendinous xanthomatosis, hereditary diffuse leukoencephalopathy with axonal spheroids, autosomal dominant adult-onset demyelinating leukodystrophy, adult polyglucosan body disease, and leukoencephalopathy with vanishing white matter. Ultimately, this Review aims to provide helpful suggestions to identify treatable adulthood leukodystrophies at an early stage in the disease course.

Engineered 3D-printed artificial axons

Myelination is critical for transduction of neuronal signals, neuron survival and normal function of the nervous system. Myelin disorders account for many debilitating neurological diseases such as multiple sclerosis and leukodystrophies. The lack of experimental models and tools to observe and manipulate this process in vitro has constrained progress in understanding and promoting myelination, and ultimately developing effective remyelination therapies. To address this problem, we developed synthetic mimics of neuronal axons, representing key geometric, mechanical, and surface chemistry components of biological axons. These artificial axons exhibit low mechanical stiffness approaching that of a human axon, over unsupported spans that facilitate engagement and wrapping by glial cells, to enable study of myelination in environments reflecting mechanical cues that neurons present in vivo. Our 3D printing approach provides the capacity to vary independently the complex features of the artificial axons that can reflect specific states of development, disease, or injury. Here, we demonstrate that oligodendrocytes' production and wrapping of myelin depend on artificial axon stiffness, diameter, and ligand coating. This biofidelic platform provides direct visualization and quantification of myelin formation and myelinating cells' response to both physical cues and pharmacological agents.

Asparagine Synthetase deficiency-report of a novel mutation and review of literature

Asparagine synthetase deficiency is a rare inborn error of metabolism caused by a defect in ASNS, a gene encoding asparagine synthetase. It manifests with a severe neurological phenotype manifesting as severe developmental delay, congenital microcephaly, spasticity and refractory seizures. To date, nineteen patients from twelve unrelated families have been identified. Majority of the mutations are missense and nonsense mutations in homozygous or compound heterozygous state. We add another case from India which harbored a novel homozygous missense variation in exon 11 and compare the current case with previously reported cases.

Challenge of phenotype estimation for optimal treatment of Krabbe disease

Krabbe disease is an autosomal recessive, inherited demyelinating disease caused by deficiency of the lysosomal enzyme galactocerebrosidase. It is recognized as one of the predominant genetic diseases showing leukodystrophy from infancy to adulthood. The clinical phenotype and genotype for this disease show considerable variation worldwide, which makes accurate diagnosis difficult. Effective therapy is limited, although hematopoietic stem cell transplantation at an early stage has been established to some extent. We report here the long-term clinical effect on juvenile Krabbe disease for two brothers who underwent hematopoietic stem cell transplantation at an early stage of their disease. We review research into genotype-phenotype correlation for the possibility of early diagnosis at a presymptomatic stage. Medical care for this intractable disease will improve in the near future as a result of the increasing awareness of its molecular pathology and improvements in medical treatment. © 2016 Wiley Periodicals, Inc.

NFU1 -Related Disorders as Key Differential Diagnosis of Cavitating Leukoencephalopathy

Genetic leukoencephalopathies represent an expanding group of inherited disorders associated with involvement of brain white matter. Cystic degeneration has been previously described with some acquired or inherited leukoencephalopathies. We describe a 6-month-old Brazilian boy with a 2-month history of severe and rapidly progressive developmental and psychomotor regression and seizures. Neurological examination showed spastic tetraparesis and lethargy. Neuroimaging showed diffuse and symmetric cavitating cystic leukoencephalopathy. Whole-exome sequencing revealed compound heterozygous mutations in the NFU1 gene, providing definite genetic diagnosis of multiple mitochondrial dysfunction syndrome type 1. We report a rare presentation of early-onset cystic leukoencephalopathy in the context of multiple mitochondrial dysfunction syndrome type 1.

Infantile Alexander Disease: Case Report and Review of Literature

Alexander Disease (AD) is an autosomal dominant leukodystrophy and occurs predominantly in infants and children. It usually results in death within ten years after onset. Among the four subtypes, infantile form comprises the most of affected individuals. It presents in the first two years of life, typically with progressive psychomotor deficiency, loss of developmental milestones, seizures, and pyramidal signs. Clinical and magnetic resonance image findings usually establish diagnosis of AD. Here, we present a case of Infantile AD with characteristic clinical and radiological features.

Neuroimmune mechanisms in Krabbe's disease

Neuroinflammation, activation of innate immune components of the nervous system followed by an adaptive immune response, is observed in most leukodystrophies and coincides with white matter pathology, disease progression, and morbidity. Despite this, there is a major gap in our knowledge of the contribution of the immune system to disease phenotype. Inflammation in Krabbe's disease has been considered a secondary effect, resulting from cell-autonomous oligodendroglial cell death or myelin loss resulting from psychosine accumulation. However, recent studies have shown immune activation preceding clinical symptoms and white matter pathology. Moreover, the therapeutic effect underlying hematopoietic stem cell transplantation, the only treatment for Krabbe's disease, has been demonstrated to occur via immunomodulation. This Review highlights recent advances in elaboration of the immune cascade involved in Krabbe's disease. Mechanistic insight into the inflammatory pathways participating in myelin and axon loss or preservation may lead to novel therapeutic approaches for this disorder. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Patient/family views on data sharing in rare diseases: study in the European LeukoTreat project

The purpose of this study was to explore patient and family views on the sharing of their medical data in the context of compiling a European leukodystrophies database. A survey questionnaire was delivered with help from referral centers and the European Leukodystrophies Association, and the questionnaires returned were both quantitatively and qualitatively analyzed. This study found that patients/families were strongly in favor of participating. Patients/families hold great hope and trust in the development of this type of research. They have a strong need for information and transparency on database governance, the conditions framing access to data, all research conducted, partnerships with the pharmaceutical industry, and they also need access to results. Our findings bring ethics-driven arguments for a process combining initial broad consent with ongoing information. On both, we propose key item-deliverables to database participants.

Engineering Stem Cells for Biomedical Applications

Stem cells are characterized by a number of useful properties, including their ability to migrate, differentiate, and secrete a variety of therapeutic molecules such as immunomodulatory factors. As such, numerous pre-clinical and clinical studies have utilized stem cell-based therapies and demonstrated their tremendous potential for the treatment of various human diseases and disorders. Recently, efforts have focused on engineering stem cells in order to further enhance their innate abilities as well as to confer them with new functionalities, which can then be used in various biomedical applications. These engineered stem cells can take on a number of forms. For instance, engineered stem cells encompass the genetic modification of stem cells as well as the use of stem cells for gene delivery, nanoparticle loading and delivery, and even small molecule drug delivery. The present Review gives an in-depth account of the current status of engineered stem cells, including potential cell sources, the most common methods used to engineer stem cells, and the utilization of engineered stem cells in various biomedical applications, with a particular focus on tissue regeneration, the treatment of immunodeficiency diseases, and cancer.

[An atypical presentation of Infantile Alexander disease lacking macrocephaly]

BACKGROUND

Alexander disease is a rare form of leukodystrophy that involves mainly astrocytes; it is inherited in an autosomal recessive manner and occurs by mutations in the GFAP gene, located on chromosome 17q21. It can occur at any age and its infantile form is characterized by macrocephaly, seizures, severe motor and cognitive delay, and progressive spasticity or ataxia.

CASE REPORT

An 8-month-old female was evaluated with a history of neurodevelopmental delay and unprovoked focal motor seizures. Physical examination showed normal head circumference, increased motor responses to tactile and noise stimuli, pyramidal signs and no visceromegalies. Widespread hypodense white matter was found on magnetic resonance and lumbar puncture showed hyperproteinorrachia. Krabbe disease was ruled out by enzymatic assay and gene sequencing of GALC. In the reassessment of the case, abnormalities in neuroimaging lead to suspicion of Alexander disease, and GFAP gene sequencing reported a pathogenic mutation in exon 4 c.716G>A, which caused a change of arginine to histidine at position 239 of the protein (p.Arg239His).

CONCLUSIONS

The radiographic signs observed in the resonance were decisive for the diagnosis, later confirmed by molecular study. It is important to consider that certain mutations are not associated with macrocephaly, which may cause delay in diagnosis.

A practical approach to diseases affecting dentate nuclei

A wide variety of diseases affect the dentate nuclei. When faced with the radiological demonstration of signal changes in the dentate nuclei, radiologists and clinical neurologists have to sieve through the many possibilities, which they do not encounter on a regular basis. This task can be challenging, and therefore, developing a clinical, radiological, and laboratory approach is important. Information on the topic is scattered and the subject has not yet been reviewed. In this review, a combined clinicoradiological approach is presented. The signal changes in T1, T2, fluid-attenuated inversion recovery (FLAIR), diffusion, susceptibility weighted, and gadolinium-enhanced images can give specific or highly suggestive patterns, which are illustrated. The role of computed tomography (CT) in the diagnostic process is discussed. Specific radiological patterns do not exist in a significant proportion of patients where the clinical and laboratory analysis becomes important. In this review, we group the clinical constellations to narrow down the differential diagnosis and highlight the diagnostic clinical signs, such as tendon xanthomas and Kayser-Fleischer rings. As will be seen, a number of these conditions are potentially reversible, and hence, their early diagnosis is desirable. Finally, key diagnostic tests and available therapies are outlined. The practical approach thus begins with the radiologist and winds its way through the clinician, towards carefully selected diagnostic tests defining the therapy options.

Late infantile metachromatic leukodystrophy: Clinical manifestations of five Taiwanese patients and Genetic features in Asia

BACKGROUND

This study was conducted to describe the clinical and genetic features of patients with late infantile metachromatic leukodystrophy.

METHODS

Clinical and genetic manifestations of five Taiwanese patients with late infantile metachromatic leukodystrophy from January 2003 to April 2014 were reviewed. The genetic features of such patients reported in Asian countries during a period of 20 years were also analyzed.

RESULTS

The median age at disease onset was 1 year and 3 months with the first clinical symptom being gait disturbance. All five patients became bed-ridden at a median age of 2 years and 5 months. Nerve conduction velocity revealed demyelinating polyneuropathy and brain MRI disclosed tigroid and leopard skin pattern of dysmyelination in all 5 patients. All patients had decreased ARSA activities in leukocytes accounting for 15.88% to 30.75% of controls. Five novel mutations, p.A316D, p.G303R, p.Q176X, p.R293X, and c.749 insGCGGGCCA, were identified in our case series. Eighteen patients, including our 5 patients, were reported in Asian countries. A total of 22 different disease-causing alleles were found, in which p.W320X was identified in Taiwan and China, and p.G101V was found in Taiwan and Korea.

CONCLUSIONS

Patients with late infantile metachromatic leukodystrophy exhibited a rapid and devastating clinical course. The pattern of dysmyelination on brain MRI together with peripheral demyelination polyneuropathy indicates that evaluation of ARSA activity in leukocytes is warranted. A wide diversity of ARSA gene mutations was noted in Asia.

Alpha-thalassemia X-linked intellectual disability syndrome identified by whole exome sequencing in two boys with white matter changes and developmental retardation

Alpha-thalassemia X-linked intellectual disability (ATRX) syndrome is a genetic syndrome caused by mutation of the ATRX gene associated with chromatin remodeling. Recently, a wide spectrum of brain MRI abnormalities and clinical manifestations has been recognized. We describe two male patients with genetically confirmed ATRX syndrome, both presented with developmental delay and white matter changes without typical clinical characteristics of ATRX. Whole-exome sequencing revealed the presence of ATRX mutations: a novel c.6472A>G mutation in Case 1 and a previously reported c.6532C>T mutation in Case 2. These two cases expanded the genetic and clinical spectrum of ATRX syndrome, including brain MRI abnormalities. Our results suggest that male patients with developmental delay and widespread white matter changes, even without distinctive facial dysmorphism and hematologic abnormalities, should be suspected as ATRX syndrome. We support the clinical utility of whole-exome sequencing, particularly in ultra-rare neurological diseases with nonspecific developmental disabilities and atypical presentation.

Non-neuronopathic lysosomal storage disorders: Disease spectrum and treatments

Distinctive facial features, hepatosplenomegaly or cardiomyopathy with or without associated skeletal dysplasia are clinical manifestations that may be suggestive of an underlying lysosomal storage disorder (LSD), However, these features may not be evident in certain subtypes associated primarily with central nervous system involvement. Age at onset can be broad, ranging from infancy to adulthood. Diagnosis may be delayed, as manifestations may be slow to evolve (taking months to years), particularly in those with later (adult-)onset, and in isolated cases (i.e., those without a prior family history). Diagnosis of individual subtypes can be confirmed using a combination of biochemical and molecular assays. In a few LSDs, treatment with hematopoietic stem cell transplantation, enzyme replacement or substrate reduction therapy is available. Symptomatic and palliative measure may enhance quality of life for both treatable and currently untreatable cases. Genetic counseling is important, so patients and their families can be informed of reproductive risks, disease prognosis and therapeutic options. Investigations of underlying disease mechanisms are enhancing knowledge about rare diseases, but also other more common medical conditions, on account of potential convergent disease pathways.

Ethical management in the constitution of a European database for leukodystrophies rare diseases

BACKGROUND

The EU LeukoTreat program aims to connect, enlarge and improve existing national databases for leukodystrophies (LDs) and other genetic diseases affecting the white matter of the brain. Ethical issues have been placed high on the agenda by pairing the participating LD expert research teams with experts in medical ethics and LD patient families and associations. The overarching goal is to apply core ethics principles to specific project needs and ensure patient rights and protection in research addressing the context of these rare diseases.

AIM

This paper looks at how ethical issues were identified and handled at project management level when setting up an ethics committee.

METHODS

Through a work performed as a co-construction between health professionals, ethics experts, and patient representatives, we expose the major ethical issues identified.

RESULTS

The committee acts as the forum for tackling specific issues tied to data sharing and patient participation: the thin line between care and research, the need for a charter establishing the commitments binding health professionals and the information items to be delivered. Ongoing feedback on the database, including delivering global results in a broad-audience format, emerged as a key recommendation. Information should be available to all patients in the partner countries developing the database and should be scaled to different patient profiles.

CONCLUSION

This work led to a number of recommendations for ensuring transparency and optimizing the partnership between scientists and patients.

Clinical exome sequencing identifies a novel TUBB4A mutation in a child with static hypomyelinating leukodystrophy

BACKGROUND

Leukodystrophies are a large group of inherited diseases of central nervous system myelin. There are few treatments, and most patients do not receive a final genetic diagnosis.

PATIENT

We report a novel presentation of a female child with hypotonia, global developmental delay, and rotatory nystagmus. Brain MRI demonstrated profound hypomyelination and minimal or no atrophy in the brain stem or cerebellum.

RESULTS

Extensive testing failed to yield a diagnosis until clinical whole-exome sequencing revealed a novel pathogenic mutation in the β-tubulin gene TUBB4A. TUBB4A is a cause of hereditary dystonia type 4 and has recently been reported to cause hypomyelination with atrophy of the basal ganglia and cerebellum.

CONCLUSIONS

This report expands the phenotypic spectrum of TUBB4A-associated neurological diseases to include static hypomyelinating leukodystrophy and supports the clinical relevance of next-generation sequencing diagnosis approaches.

Imaging manifestations of the leukodystrophies, inherited disorders of white matter

The leukodystrophies are a diverse set of inherited white matter disorders and are uncommonly encountered by radiologists in everyday practice. As a result, it is challenging to recognize these disorders and to provide a useful differential for the referring physician. In this article, leukodystrophies are reviewed from the perspective of 4 imaging patterns: global myelination delay, periventricular/deep white matter predominant, subcortical white matter predominant, and mixed white/gray matter involvement patterns. Special emphasis is placed on pattern recognition and unusual combinations of findings that may suggest a specific diagnosis.

Central and peripheral demyelination

Several conditions cause damage to the inherently normal myelin of central nervous system, perepheral nervous system or both central and perepheral nervous system and hence termed as central demyelinating diseases, perepheral demyelinating diseases and combined central and perepheral demyelinating diseases respectively. Here we analysed and foccused on the etiology, prevalance, incidence and age of these demyelinating disorders. Clinical attention and various diagnostic tests are needed to adequately assess all these possibilities.

Oligodendrogenesis and myelinogenesis during postnatal development effect of glatiramer acetate

Myelinogenesis in the mammal nervous system occurs predominantly postnatally. Glatiramer acetate (GA), a drug for the treatment for multiple sclerosis (MS), has been shown to induce immunomodulation and neuroprotection in the inflamed CNS in MS and in experimental autoimmune encephalomyelitis (EAE). Here we investigated whether GA can affect myelinogenesis and oligodendrogenesis in the developing nervous system under nonpathological conditions. Towards this end we studied myelination in mice injected daily by GA, at postnatal Days 7-21. Immunohistological and ultrastructural analyses revealed significant elevation in the number of myelinated axons as well as in the thickness of the myelin encircling them and their resulting g-ratios, in spinal cords of GA-injected mice compared with their PBS-injected littermates, at postnatal Day 14. Elevation in myelinated axons was detected also in the peripheral ventral roots of the motor nerves. GA induced also an increase in axonal diameter, implying an effect on the overall development of the nervous system. A prominent elevation in the amount of progenitor oligodendrocytes and their BrdU incorporation, as well as in mature oligodendrocytes indicated that the effect of GA is linked to increased proliferation and differentiation along the oligodendroglial maturation cascade. In addition, elevation in insulin-like growth factor (IGF-1) and brain-derived neurotrophic factor (BDNF) was found in the white matter of the GA-injected mice. Furthermore, a functional advantage in rotating rod test was exhibited by GA-injected mice over their littermates at postnatal Day 21. These cumulative findings corroborate the beneficial effect of GA on oligodendrogenesis and myelination.

National variation in costs and mortality for leukodystrophy patients in US children's hospitals

BACKGROUND

Inherited leukodystrophies are progressive, debilitating neurological disorders with few treatment options and high mortality rates. Our objective was to determine national variation in the costs for leukodystrophy patients and to evaluate differences in their care.

METHODS

We developed an algorithm to identify inherited leukodystrophy patients in deidentified data sets using a recursive tree model based on International Classification of Disease, 9th Edition, Clinical Modification, diagnosis and procedure charge codes. Validation of the algorithm was performed independently at two institutions, and with data from the Pediatric Health Information System (PHIS) of 43 US children's hospitals, for a 7-year period between 2004 and 2010.

RESULTS

A recursive algorithm was developed and validated, based on six International Classification of Disease, 9th Edition, Clinical Modification, codes and one procedure code that had a sensitivity up to 90% (range 61-90%) and a specificity up to 99% (range 53-99%) for identifying inherited leukodystrophy patients. Inherited leukodystrophy patients comprise 0.4% of admissions to children's hospitals and 0.7% of costs. During 7 years, these patients required $411 million of hospital care, or $131,000/patient. Hospital costs for leukodystrophy patients varied at different institutions, ranging from two to 15 times more than the average pediatric patient. There was a statistically significant correlation between higher volume and increased cost efficiency. Increased mortality rates had an inverse relationship with increased patient volume that was not statistically significant.

CONCLUSIONS

We developed and validated a code-based algorithm for identifying leukodystrophy patients in deidentified national datasets. Leukodystrophy patients account for $59 million of costs yearly at children's hospitals. Our data highlight potential to reduce unwarranted variability and improve patient care.