The burden of inherited leukodystrophies in children

Randomized Clinical Trial of First-Line Genome Sequencing in Pediatric White Matter Disorders

OBJECTIVE

Genome sequencing (GS) is promising for unsolved leukodystrophies, but its efficacy has not been prospectively studied.

METHODS

A prospective time-delayed crossover design trial of GS to assess the efficacy of GS as a first-line diagnostic tool for genetic white matter disorders took place between December 1, 2015 and September 27, 2017. Patients were randomized to receive GS immediately with concurrent standard of care (SoC) testing, or to receive SoC testing for 4 months followed by GS.

RESULTS

Thirty-four individuals were assessed at interim review. The genetic origin of 2 patient's leukoencephalopathy was resolved before randomization. Nine patients were stratified to the immediate intervention group and 23 patients to the delayed-GS arm. The efficacy of GS was significant relative to SoC in the immediate (5/9 [56%] vs 0/9 [0%]; Wild-Seber, p < 0.005) and delayed (control) arms (14/23 [61%] vs 5/23 [22%]; Wild-Seber, p < 0.005). The time to diagnosis was significantly shorter in the immediate-GS group (log-rank test, p = 0.04). The overall diagnostic efficacy of combined GS and SoC approaches was 26 of 34 (76.5%, 95% confidence interval = 58.8-89.3%) in <4 months, greater than historical norms of <50% over 5 years. Owing to loss of clinical equipoise, the trial design was altered to a single-arm observational study.

INTERPRETATION

In this study, first-line GS provided earlier and greater diagnostic efficacy in white matter disorders. We provide an evidence-based diagnostic testing algorithm to enable appropriate clinical GS utilization in this population. ANN NEUROL 2020;88:264-273.

Leukodystrophies and Genetic Leukoencephalopathies in Children Specified by Exome Sequencing in an Expanded Gene Panel

The overlapping clinical and neuroimaging phenotypes of leukodystrophies pose a diagnostic challenge to both clinicians and researchers alike. Studies on the application of exome sequencing in the diagnosis of leukodystrophies are emerging. We used targeted gene panel sequencing of 6440 genes to investigate the genetic etiology in a cohort of 50 children with neuroimaging diagnosis of leukodystrophy/genetic leukoencephalopathy of unknown etiology. These 50 patients without a definite biochemical or genetic diagnosis were derived from a cohort of 88 patients seen during a 2.5-year period (2015 January-2017 June). Patients who had diagnosis by biochemical or biopsy confirmation (n = 17) and patients with incomplete data or lack of follow-up (n = 21) were excluded. Exome sequencing identified variants in 30 (60%) patients, which included pathogenic or likely pathogenic variants in 28 and variants of unknown significance in 2. Among the patients with pathogenic or likely pathogenic variants, classic leukodystrophies constituted 13 (26%) and genetic leukoencephalopathies 15 (30%). The clinical and magnetic resonance imaging (MRI) findings and genetic features of the identified disorders are discussed.

Geographic and Specialty Access Disparities in US Pediatric Leukodystrophy Diagnosis

OBJECTIVE

To examine disparities in the diagnosis of leukodystrophies including geographic factors and access to specialty centers.

STUDY DESIGN

Retrospective cohort study of pediatric patients admitted to Pediatric Health Information System hospitals. Patients with leukodystrophy were identified with International Classification of Diseases, Tenth Revision, Clinical Modification diagnostic codes for any of 4 leukodystrophies (X-linked adrenoleukodystrophy, Hurler disease, Krabbe disease, and metachromatic leukodystrophy). We used 3-level hierarchical generalized logistic modeling to predict diagnosis of a leukodystrophy based on distance traveled for hospital, neighborhood composition, urban/rural context, and access to specialty center.

RESULTS

We identified 501 patients with leukodystrophy. Patients seen at a leukodystrophy center of excellence hospital were 1.73 times more likely to be diagnosed than patients at non-center of excellence hospitals. Patients who traveled farther were more likely to be diagnosed than those who traveled shorter. Patients living in a Health Professionals Shortage Area zip code were 0.86 times less likely to be diagnosed than those living in a non-Health Professionals Shortage Area zip code.

CONCLUSIONS

Geographic factors affect the diagnosis of leukodystrophies in pediatric patients, particularly in regard to access to a center with expertise in leukodystrophies. Our findings suggest a need for improving access to pediatric specialists and possibly deploying specialists or diagnostic testing more broadly.

Novel variants underlying autosomal recessive intellectual disability in Pakistani consanguineous families

Background

Intellectual disability (ID) is both a clinically diverse and genetically heterogeneous group of disorder, with an onset of cognitive impairment before the age of 18 years. ID is characterized by significant limitations in intellectual functioning and adaptive behaviour. The identification of genetic variants causing ID and neurodevelopmental disorders using whole-exome sequencing (WES) has proven to be successful. So far more than 1222 primary and 1127 candidate genes are associated with ID.

Methods

To determine pathogenic variants causative of ID in three unrelated consanguineous Pakistani families, we used a combination of WES, homozygosity-by-descent mapping, de-deoxy sequencing and bioinformatics analysis.

Results

Rare pathogenic single nucleotide variants identified by WES which passed our filtering strategy were confirmed by traditional Sanger sequencing and segregation analysis. Novel and deleterious variants in VPS53, GLB1, and MLC1, genes previously associated with variable neurodevelopmental anomalies, were found to segregate with the disease in the three families.

Conclusions

This study expands our knowledge on the molecular basis of ID as well as the clinical heterogeneity associated to different rare genetic causes of neurodevelopmental disorders. This genetic study could also provide additional knowledge to help genetic assessment as well as clinical and social management of ID in Pakistani families.

Racial/Ethnic and Insurance Status Disparities in Distance Traveled to Access Children's Hospital Care for Severe Illness: the Case of Children with Leukodystrophies

Families of children with special health care needs may travel substantial distances to access specialized health care. However, it is not known how race/ethnicity, insurance status, and access to disease-specific specialty care affect travel distances. This analysis examines patients aged 18 years or younger who were discharged from a Pediatric Health Information System (PHIS) children's hospital (n = 52) with a diagnosis of an inherited leukodystrophy between October 1, 2015, and September 30, 2018 (n = 950 patients). Leukodystrophies are rare but very serious neurological illnesses, with elevated mortality and morbidity rates. Bivariate and hierarchical generalized linear models reveal that white children, privately insured children, and children visiting leukodystrophy specialist centers travel farther for children's hospital care. These findings indicate that socially privileged families travel greater distances to obtain specialized health care, which could affect clinical outcomes.

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.

Distinct patterns of complex rearrangements and a mutational signature of microhomeology are frequently observed in PLP1 copy number gain structural variants

BACKGROUND

We investigated the features of the genomic rearrangements in a cohort of 50 male individuals with proteolipid protein 1 (PLP1) copy number gain events who were ascertained with Pelizaeus-Merzbacher disease (PMD; MIM: 312080). We then compared our new data to previous structural variant mutagenesis studies involving the Xq22 region of the human genome. The aggregate data from 159 sequenced join-points (discontinuous sequences in the reference genome that are joined during the rearrangement process) were studied. Analysis of these data from 150 individuals enabled the spectrum and relative distribution of the underlying genomic mutational signatures to be delineated.

METHODS

Genomic rearrangements in PMD individuals with PLP1 copy number gain events were investigated by high-density customized array or clinical chromosomal microarray analysis and breakpoint junction sequence analysis.

RESULTS

High-density customized array showed that the majority of cases (33/50; ~ 66%) present with single duplications, although complex genomic rearrangements (CGRs) are also frequent (17/50; ~ 34%). Breakpoint mapping to nucleotide resolution revealed further previously unknown structural and sequence complexities, even in single duplications. Meta-analysis of all studied rearrangements that occur at the PLP1 locus showed that single duplications were found in ~ 54% of individuals and that, among all CGR cases, triplication flanked by duplications is the most frequent CGR array CGH pattern observed. Importantly, in ~ 32% of join-points, there is evidence for a mutational signature of microhomeology (highly similar yet imperfect sequence matches).

CONCLUSIONS

These data reveal a high frequency of CGRs at the PLP1 locus and support the assertion that replication-based mechanisms are prominent contributors to the formation of CGRs at Xq22. We propose that microhomeology can facilitate template switching, by stabilizing strand annealing of the primer using W-C base complementarity, and is a mutational signature for replicative repair.

Clinical approach to neurodegenerative disorders in childhood: an updated overview

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

Pelizaeus-Merzbacher Disease: Molecular and Cellular Pathologies and Associated Phenotypes

Pelizaeus-Merzbacher disease (PMD) represents a group of disorders known as hypomyelinating leukodystrophies, which are characterized by abnormal development and maintenance of myelin in the central nervous system. PMD is caused by different types of mutations in the proteolipid protein 1 (PLP1) gene, which encodes a major myelin membrane lipoprotein. These mutations in the PLP1 gene result in distinct cellular and molecular pathologies and a spectrum of clinical phenotypes. In this chapter, I discuss the historical aspects and current understanding of the mechanisms underlying how different PLP1 mutations disrupt the normal process of myelination and result in PMD and other disorders.

Scope and Burden of Non-Standard of Care Hematopoietic Stem Cell Transplantation in Pediatric Leukodystrophy Patients

Inherited leukodystrophies are a group of diseases affecting central nervous system myelin that lead to death or significant health problems. Although for most leukodystrophies there are no curative treatments, for a handful of diseases hematopoietic stem cell transplantation (HSCT; bone marrow transplant) can stop disease progression, and if initiated in a timely fashion, prevent many or all neurologic and other systems involvement. However, HSCT is a complex procedure with significant morbidity and mortality risks. The study goal was to determine whether HSCT was being more widely used outside of those leukodystrophies for which HSCT is typically employed. The authors conducted a 2-year retrospective review of HSCT performed across the United States in 51 children's hospitals that are part of the Pediatric Health Information System. The authors screened for 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) codes for leukodystrophies in which HSCT is "nonstandard," including sphingolipidoses, Fabry disease, Gaucher disease, and Niemann-Pick disease, and excluded patients who had ICD-10 codes for leukodystrophies that are HSCT candidates, specifically X-linked adrenoleukodystrophy, metachromatic leukodystrophy, Krabbe disease, and Hurler disease. The authors identified 91 patients (from a total cohort of 937) with one of the nonstandard leukodystrophies who had HSCT. HSCT was performed at 20 of the hospitals, with the majority performed at only 6 hospitals. Average costs ($786 846) per patient were more than 6 times higher than patients who did not have HSCT. The data show that an unexpectedly large number of leukodystrophy patients are receiving transplants for conditions in which HSCT is not typically used, and which are associated with high medical costs.

Association of Diagnosis of Leukodystrophy With Race and Ethnicity Among Pediatric and Adolescent Patients

IMPORTANCE

Inherited leukodystrophies are a group of neurological diseases affecting myelin that cause significant morbidities and death. Timely and correct diagnosis is important for initiating treatment, designing disease screening, and offering care and guidance to patients and families.

OBJECTIVE

To determine whether there are disparities in leukodystrophy diagnosis in different racial backgrounds.

DESIGN, SETTING, AND PARTICIPANTS

This case-control study involved a retrospective review of patients aged 18 years or younger who were diagnosed with 1 of 4 leukodystrophies (metachromatic leukodystrophy, X-linked adrenoleukodystrophy, Krabbe disease, and Hurler disease) in the US Children's Hospital Association's Pediatric Health Information System database from October 1, 2015, through September 30, 2017.

MAIN OUTCOMES AND MEASURES

Leukodystrophy diagnosis and racial background of the patients were analyzed. Adjusted prevalence estimates of leukodystrophies were obtained by controlling for sex, insurance type, urban or rural status, 2010 median household income for patient zip code, number of inpatient days, and age at first visit. Pathogenic leukodystrophy gene allele frequencies in different racial backgrounds for ABCD1, ARSA, GALC, and IDUA were determined using the gnomAD database.

RESULTS

Of the 557 patients identified with a leukodystrophy (221 [40%] female; 321 [58%] white non-Hispanic, 54 [10%] black non-Hispanic, and 51 [9%] white Hispanic; median [range] age, 7 [0-18] years), nonwhite race, including black non-Hispanic, black Hispanic, and white Hispanic, was associated with not having a leukodystrophy diagnosis. The adjusted prevalence for a leukodystrophy diagnosis in white non-Hispanic patients was 13.8 (95% CI, 10.6-17.9) per 100 000 patients, compared with 5.8 (95% CI, 3.8-8.9), 2.4 (95% CI, 1.1-5.2), and 7.4 (95% CI, 5.2-10.4) per 100 000 in black non-Hispanic, black Hispanic, and white Hispanic patients, respectively. This reduced rate of diagnosis was out of proportion to the frequency of the different races in the Pediatric Health Information System database. Similar or higher frequencies of missense or loss-of-function alleles were measured in populations of Latino and African descent for the pathogenic leukodystrophy gene alleles. For example, for ABCD1, allele frequencies in those of Latino or African descent were 2.1 × 10-5 and 2.2 × 10-5, as compared with 1.4 × 10-5 for those of European non-Finnish descent.

CONCLUSIONS AND RELEVANCE

Patients of racial/ethnic minorities, including those from black, black Hispanic, and white Hispanic backgrounds, were significantly less likely to be diagnosed with a leukodystrophy. Leukodystrophy disease-associated allele frequencies were the same or higher in populations of Latino or African descent, arguing against a genetic founder effect being responsible for the lower diagnosis rates. This underdiagnosis has implications for newborn screening programs and treatment access and may reflect a more widespread problem in pediatric neurological and orphan diseases.

Chemical Screening Identifies Enhancers of Mutant Oligodendrocyte Survival and Unmasks a Distinct Pathological Phase in Pelizaeus-Merzbacher Disease

Pelizaeus-Merzbacher disease (PMD) is a fatal X-linked disorder caused by loss of myelinating oligodendrocytes and consequent hypomyelination. The underlying cellular and molecular dysfunctions are not fully defined, but therapeutic enhancement of oligodendrocyte survival could restore functional myelination in patients. Here we generated pure, scalable quantities of induced pluripotent stem cell-derived oligodendrocyte progenitor cells (OPCs) from a severe mouse model of PMD, Plp1jimpy. Temporal phenotypic and transcriptomic studies defined an early pathological window characterized by endoplasmic reticulum (ER) stress and cell death as OPCs exit their progenitor state. High-throughput phenotypic screening identified a compound, Ro 25-6981, which modulates the ER stress response and rescues mutant oligodendrocyte survival in jimpy, in vitro and in vivo, and in human PMD oligocortical spheroids. Surprisingly, increasing oligodendrocyte survival did not restore subsequent myelination, revealing a second pathological phase. Collectively, our work shows that PMD oligodendrocyte loss can be rescued pharmacologically and defines a need for multifactorial intervention to restore myelination.

Natural History of Vanishing White Matter

OBJECTIVE

To comprehensively describe the natural history of vanishing white matter (VWM), aiming at improving counseling of patients/families and providing natural history data for future therapeutic trials.

METHODS

We performed a longitudinal multicenter study among 296 genetically confirmed VWM patients. Clinical information was obtained via disease-specific clinical questionnaire, Health Utilities Index and Guy's Neurological Disability Scale assessments, and chart review.

RESULTS

First disease signs occurred at a median age of 3 years (mode = 2 years, range = before birth to 54 years); 60% of patients were symptomatic before the age of 4 years. The nature of the first signs varied for different ages of onset. Overall, motor problems were the most common presenting sign, especially in children. Adolescent and adult onset patients were more likely to exhibit cognitive problems early after disease onset. One hundred two patients were deceased. Multivariate Cox regression analysis revealed a positive relation between age at onset and both preservation of ambulation and survival. Absence of stress-provoked episodes and absence of seizures predicted more favorable outcome. In patients with onset before 4 years, earlier onset was associated with more severe disability and higher mortality. For onset from 4 years on, disease course was generally milder, with a wide variation in severity. There were no significant differences for sex or for the 5 eIF2B gene groups. The results confirm the presence of a genotype-phenotype correlation.

INTERPRETATION

The VWM disease spectrum consists of a continuum with extremely wide variability. Age at onset is a strong predictor for disease course. Ann Neurol 2018;84:274-288.

Absence of Axoglial Paranodal Junctions in a Child With CNTNAP1 Mutations, Hypomyelination, and Arthrogryposis

Leukodystrophies and genetic leukoencephalopathies are a heterogeneous group of heritable disorders that affect the glial-axonal unit. As more patients with unsolved leukodystrophies and genetic leukoencephalopathies undergo next generation sequencing, causative mutations in genes leading to central hypomyelination are being identified. Two such individuals presented with arthrogryposis multiplex congenita, congenital hypomyelinating neuropathy, and central hypomyelination with early respiratory failure. Whole exome sequencing identified biallelic mutations in the CNTNAP1 gene: homozygous c.1163G>C (p.Arg388Pro) and compound heterozygous c.967T>C (p.Cys323Arg) and c.319C>T (p.Arg107*). Sural nerve and quadriceps muscle biopsies demonstrated progressive, severe onion bulb and axonal pathology. By ultrastructural evaluation, septate axoglial paranodal junctions were absent from nodes of Ranvier. Serial brain magnetic resonance images revealed hypomyelination, progressive atrophy, and reduced diffusion in the globus pallidus in both patients. These 2 families illustrate severe progressive peripheral demyelinating neuropathy due to the absence of septate paranodal junctions and central hypomyelination with neurodegeneration in CNTNAP1-associated arthrogryposis multiplex congenita.

Novel PLP1 Mutations Identified With Next-Generation Sequencing Expand the Spectrum of PLP1-Associated Leukodystrophy Clinical Phenotypes

Next-generation sequencing was performed for 2 families with an undiagnosed neurologic disease. Analysis revealed X-linked mutations in the proteolipid protein 1 (PLP1) gene, which is associated with X-linked Pelizaeus-Merzbacher disease and Spastic Paraplegia type 2. In family A, the novel PLP1 missense mutation c.617T>A (p.M206K) was hemizygous in the 2 affected male children and heterozygous in the mother. In family B, the novel de novoPLP1 frameshift mutation c.359_369del (p.G120fs) was hemizygous in the affected male child. Although PLP1 mutations have been reported to cause an increasingly wide range of phenotypes inclusive of the dystonia, spastic paraparesis, motor neuronopathy, and leukodystrophy observed in our patients, atypical features included the cerebrospinal fluid deficiency of neurotransmitter and pterin metabolites and the delayed appearance of myelin abnormalities on neuroimaging studies. Next-generation sequencing studies provided a diagnosis for these families with complex leukodystrophy disease phenotypes, which expanded the spectrum of PLP1-associated leukodystrophy clinical phenotypes.

Clinical and mutational spectrum of Colombian patients with Pelizaeus Merzbacher Disease

CASE PRESENTATION

Pelizaeus Merzbacher Disease (PMD) is an X-linked developmental defect of myelination that causes childhood chronic spastic encephalopathy. Its genetic etiology can be either a duplication (or other gene dosage alterations) or a punctual mutation at the PLP1 locus. Clinically, it presents with developmental delay, nystagmus and, spasticity, supported by neuroimaging in which the defect of myelination is evident. We present a series of seven Colombian patients diagnosed with this leucodystrophy, describing their genotypic and phenotypic characteristics and heterogeneity.

CLINICAL FINDINGS

All patients included were male, 6 months to 16 years of age. Mean age at onset of symptoms was 8 months. Mean age at diagnosis was 5 years 5 months, being classic PMD most frequently diagnosed, as compared to the connatal phenotype. All cases had a primary diagnosis of developmental delay on 100%, and in 28.7% of cases, early onset nystagmus was described. 85.7% of patients had spasticity, 71.4% cerebellar signs, 57.0% hypotonia, and 28.5% had an abnormal movement disorder. Only three patients were able to achieve gait, though altered. In the two patients who had a diagnosis of connatal PMD maturational ages in danger zones according to the WHO Abbreviated Scale of Psychosocial Development were documented. All cases had abnormalities in neuroimages.

MOLECULAR ANALYSIS AND RESULTS

Molecular studies were used in the majority of the cases to confirm the diagnosis (85.7 %). For two cases molecular confirmation was not considered necessary given their affected male brothers had already been tested. PLP1 gene dosage alterations (duplications) were found in 28.5 % of the patients (two siblings), whereas three different single nucleotide variants were detected.

CLINICAL RELEVANCE

According to these findings, as authors we propose the diagnostic algorithm in Colombian population to begin on a high clinical suspicion, followed by paraclinical extension, moving on to the molecular confirmation by using approaches to simultaneously sequence the PLP1 gene in order to detect point mutations and in/dels and performing a copy number variation analysis for the detection of gene dosage alterations.

Update on pediatric-onset multiple sclerosis

Pediatric-onset multiple sclerosis (POMS) has distinctive features compared with adult-onset multiple sclerosis (AOMS), and warrants caution despite being a rare form of MS. POMS diagnostic criteria are somewhat different from those used in AOMS, with acute disseminated encephalomyelitis being a key differential diagnosis of MS in children. Other differential diagnoses that have to be ruled out before diagnosing MS include demyelinating syndromes, autoimmune and systemic pathologies, and infectious, genetic, metabolic and neoplastic diseases. Compared with AOMS, POMS has several different clinical, biological and imaging findings. At onset, high-level inflammatory activity is mainly reported, and patients with POMS are also at high risk of developing early physical disabilities and early cognitive impairment. Yet, treating patients with POMS is challenging due to a lack of randomized controlled trials. Some of the disease-modifying drugs currently prescribed are analogous to therapies used in adults, and are associated with good tolerability in pediatric patients. However, a few clinical trials dedicated to POMS are now in progress, and the future outlook is to improve the long-term prognosis of POMS patients with early effective and safe treatments.

Magnetic resonance imaging in the diagnosis of white matter signal abnormalities

Background White matter abnormalities (WMAs) pose a diagnostic challenge when trying to establish etiologic diagnoses. During childhood and adult years, genetic disorders, metabolic disorders and acquired conditions are included in differential diagnoses. To assist clinicians and radiologists, a structured algorithm using cranial magnetic resonance imaging (MRI) has been recommended to aid in establishing working diagnoses that facilitate appropriate biochemical and genetic investigations. This retrospective pilot study investigated the validity and diagnostic utility of this algorithm when applied to white matter signal abnormalities (WMSAs) reported on imaging studies of patients seen in our clinics. Methods The MRI algorithm was applied to 31 patients selected from patients attending the neurometabolic/neurogenetic/metabolic/neurology clinics at a tertiary care hospital. These patients varied in age from 5 months to 79 years old, and were reported to have WMSAs on cranial MRI scans. Twenty-one patients had confirmed WMA diagnoses and 10 patients had non-specific WMA diagnoses (etiology unknown). Two radiologists, blinded to confirmed diagnoses, used clinical abstracts and the WMSAs present on patient MRI scans to classify possible WMA diagnoses utilizing the algorithm. Results The MRI algorithm displayed a sensitivity of 100%, a specificity of 30.0% and a positive predicted value of 74.1%. Cohen's kappa statistic for inter-radiologist agreement was 0.733, suggesting "good" agreement between radiologists. Conclusions Although a high diagnostic utility was not observed, results suggest that this MRI algorithm has promise as a clinical tool for clinicians and radiologists. We discuss the benefits and limitations of this approach.

The First Report of Relative Incidence of Inherited White Matter Disorders in an Asian Country Based on an Iranian Bioregistry System

Childhood leukodystrophies are a fast-growing field of pediatric neurology practice. Epidemiologic studies on the incidence of these disorders in children show different results. This is the first report of childhood leukodystrophies incidence from Iran. The enrolled patients were recruited from the neurometabolic bioregistry system that was organized in 2010 in the Children's Medical Center, Tehran, Iran. Herein is reported the incidence rate of leukodystrophies in those patients who were residents of 2 big popular provinces near Iran's capital city Tehran, with an average child population of 2 988 800 children. Ninety cases of leukodystrophies from Tehran and Alborz provinces who were registered between 2010 and 2016 in the bioregistry system were enrolled in this study. The annual incidence of inherited white matter disorders was 3.01/100 000, the highest number compared with those found in other studies using similar methods throughout the world. One of the main cause of this higher incidence could be the higher number of consanguineous marriages in Iran.

A zebrafish model of X-linked adrenoleukodystrophy recapitulates key disease features and demonstrates a developmental requirement for abcd1 in oligodendrocyte patterning and myelination

X-linked adrenoleukodystrophy (ALD) is a devastating inherited neurodegenerative disease caused by defects in the ABCD1 gene and affecting peripheral and central nervous system myelin. ABCD1 encodes a peroxisomal transmembrane protein required for very long chain fatty acid (VLCFA) metabolism. We show that zebrafish (Danio rerio) Abcd1 is highly conserved at the amino acid level with human ABCD1, and during development is expressed in homologous regions including the central nervous system and adrenal glands. We used TALENs to generate five zebrafish abcd1 mutant allele lines introducing premature stop codons in exon 1, as well as obtained an abcd1 allele from the Zebrafish Mutation Project carrying a point mutation in a splice donor site. Similar to patients with ALD, zebrafish abcd1 mutants have elevated VLCFA levels. Interestingly, we found that CNS development of the abcd1 mutants is disrupted, with hypomyelination in the spinal cord, abnormal patterning and decreased numbers of oligodendrocytes, and increased cell death. By day of life five abcd1 mutants demonstrate impaired motor function, and overall survival to adulthood of heterozygous and homozygous mutants is decreased. Expression of human ABCD1 in oligodendrocytes rescued apoptosis in the abcd1 mutant. In summary, we have established a zebrafish model of ALD that recapitulates key features of human disease pathology and which reveals novel features of underlying disease pathogenesis.

Early and late outcomes after cord blood transplantation for pediatric patients with inherited leukodystrophies

Leukodystrophies (LD) are devastating inherited disorders leading to rapid neurological deterioration and premature death. Hematopoietic stem cell transplantation (HSCT) can halt disease progression for selected LD. Cord blood is a common donor source for transplantation of these patients because it is rapidly available and can be used without full HLA matching. However, precise recommendations allowing care providers to identify patients who benefit from HSCT are lacking. In this study, we define risk factors and describe the early and late outcomes of 169 patients with globoid cell leukodystrophy, X-linked adrenoleukodystrophy, and metachromatic leukodystrophy undergoing cord blood transplantation (CBT) at an European Society for Blood and Marrow Transplantation center or at Duke University Medical Center from 1996 to 2013. Factors associated with higher overall survival (OS) included presymptomatic status (77% vs 49%; P = .006), well-matched (≤1 HLA mismatch) CB units (71% vs 54%; P = .009), and performance status (PS) of >80 vs <60 or 60 to 80 (69% vs 32% and 55%, respectively; P = .003). For patients with PS≤60 (n = 20) or 60 to 80 (n = 24) pre-CBT, only 4 (9%) showed improvement. Of the survivors with PS >80 pre-CBT, 50% remained stable, 20% declined to 60 to 80, and 30% to <60. Overall, an encouraging OS was found for LD patients after CBT, especially for those who are presymptomatic before CBT and received adequately dosed grafts. Early identification and fast referral to a specialized center may lead to earlier treatment and, subsequently, to improved outcomes.

Pediatric leukodystrophies: The role of the otolaryngologist

BACKGROUND

Leukodystrophies consist of degenerative neurogenetic diseases often associated with comorbidities that extend beyond the neurological system. Despite their impacts on patients' quality of life and risks of complications, head and neck symptomology is poorly reported in the literature. The objective of this study was to identify and quantify the main head and neck complaints among a cohort of patients diagnosed with leukodystrophies and define the role of the otolaryngologist as part of a multidisciplinary team for treating these patients.

METHODS

During the First Canadian National Conference on Leukodystrophies held at the Montreal's Children Hospital, a cohort of 12 patients diagnosed with leukodystrophies were recruited and evaluated by a multidisciplinary team. An otolaryngology-focused assessment was done through history and physical examination, and included a screening questionnaire for 23 common otolaryngology issues. If families reported a history of sialorrhea, a validated questionnaire (Drool Quality of Life Assessment Questionnaire (DroolQoL)) was subsequently distributed. Results from the questionnaires were then compiled and analyzed.

RESULTS

Of the 12 recruited patients, 83% (10/12) were known to an otolaryngologist. Drooling affected 67% (8/12) of patients although only 37.5% (3/8) of patients had undergone medical or surgical therapies for this issue. Four patients experienced at least one aspiration pneumonia. 58% (7/12) of the patients had dysphagia, of whom 43% (3/12) were fed exclusively via gastrostomy tube and 28% (2/7) required thickening of feeds. Two patients, despite suspicion of dysphagia and aspiration, had never undergone evaluation. As for otologic issues, it was noted that 25% (3/12) of patients had a history of pressure equalizing tubes (PETs) and one patient had a history of hearing loss.

CONCLUSION

Head and neck comorbidities affect children with leukodystrophies. Therefore, the otolaryngologist should be part of the multidisciplinary team, specifically for the management of dysphagia and sialorrhea.

Revised consensus statement on the preventive and symptomatic care of patients with leukodystrophies

Leukodystrophies are a broad class of genetic disorders that result in disruption or destruction of central myelination. Although the mechanisms underlying these disorders are heterogeneous, there are many common symptoms that affect patients irrespective of the genetic diagnosis. The comfort and quality of life of these children is a primary goal that can complement efforts directed at curative therapies. Contained within this report is a systems-based approach to management of complications that result from leukodystrophies. We discuss the initial evaluation, identification of common medical issues, and management options to establish a comprehensive, standardized care approach. We will also address clinical topics relevant to select leukodystrophies, such as gallbladder pathology and adrenal insufficiency. The recommendations within this review rely on existing studies and consensus opinions and underscore the need for future research on evidence-based outcomes to better treat the manifestations of this unique set of genetic disorders.

Bergmann glia translocation: a new disease marker for vanishing white matter identifies therapeutic effects of Guanabenz treatment

AIM

Vanishing White Matter (VWM) is a devastating leucoencephalopathy without effective treatment options. Patients have mutations in the EIF2B1-5 genes, encoding the five subunits of eIF2B, a guanine exchange factor that is an important regulator of protein translation. We recently developed mouse models for VWM that replicate the human disease. To study disease improvement after treatment in these mice, it is essential to have sensitive biomarkers related to disease stage. The Bergmann glia of the cerebellum, an astrocytic subpopulation, translocate into the molecular layer in symptomatic VWM mice and patients. This study looked at the prospects of using Bergmann glia pathology as an objective disease marker for VWM.

METHODS

We defined a new quantitative measurement of Bergmann glia pathology in the cerebellum of VWM mice and patients. To test the sensitivity of this new marker for improvement, VWM mutant mice received long-term treatment with Guanabenz, an FDA-approved anti-hypertensive agent affecting eIF2B activity.

RESULTS

Bergmann glia translocation was significantly higher in symptomatic VWM mice and VWM patients than in controls and worsened over the disease course. Both Bergmann glia pathology and cerebellar myelin pathology improved with Guanabenz treatment in mice, showing that Bergmann glia translocation is a sensitive measurement for improvement.

CONCLUSIONS

Bergmann glia translocation can be used to objectively assess effects of treatment in VWM mice. Future treatment strategies involving compounds regulating eIF2 phosphorylation might benefit VWM patients.

Childhood leukodystrophies: A literature review of updates on new definitions, classification, diagnostic approach and management

Childhood leukodystrophies are a growing category of neurological disorders in pediatric neurology practice. With the help of new advanced genetic studies such as whole exome sequencing (WES) and whole genome sequencing (WGS), the list of childhood heritable white matter disorders has been increased to more than one hundred disorders. During the last three decades, the basic concepts and definitions, classification, diagnostic approach and medical management of these disorders much have changed. Pattern recognition based on brain magnetic resonance imaging (MRI), has played an important role in this process. We reviewed the last Global Leukodystrophy Initiative (GLIA) expert opinions in definition, new classification, diagnostic approach and medical management including emerging treatments for pediatric leukodystrophies.

The under reporting of recruitment strategies in research with children with life-threatening illnesses: A systematic review

BACKGROUND

Researchers report difficulties in conducting research with children and young people with life-limiting conditions or life-threatening illnesses and their families. Recruitment is challenged by barriers including ethical, logistical and clinical considerations.

AIM

To explore how children and young people (aged 0-25 years) with life-limiting conditions or life-threatening illnesses and their families were identified, invited and consented to research published in the last 5 years.

DESIGN

Systematic review.

DATA SOURCES

MEDLINE, PsycINFO, Web of Science, Sciences Citation Index and SCOPUS were searched for original English language research published between 2009 and 2014, recruiting children and young people with life-limiting conditions or life-threatening illness and their families.

RESULTS

A total of 215 studies - 152 qualitative, 54 quantitative and 9 mixed methods - were included. Limited recruitment information but a range of strategies and difficulties were provided. The proportion of eligible participants from those screened could not be calculated in 80% of studies. Recruitment rates could not be calculated in 77%. A total of 31% of studies recruited less than 50% of eligible participants. Reasons given for non-invitation included missing clinical or contact data, or clinician judgements of participant unsuitability. Reasons for non-participation included lack of interest and participants' perceptions of potential burdens.

CONCLUSION

All stages of recruitment were under reported. Transparency in reporting of participant identification, invitation and consent is needed to enable researchers to understand research implications, bias risk and to whom results apply. Research is needed to explore why consenting participants decide to take part or not and their experiences of research recruitment.

Modeling the Mutational and Phenotypic Landscapes of Pelizaeus-Merzbacher Disease with Human iPSC-Derived Oligodendrocytes

Pelizaeus-Merzbacher disease (PMD) is a pediatric disease of myelin in the central nervous system and manifests with a wide spectrum of clinical severities. Although PMD is a rare monogenic disease, hundreds of mutations in the X-linked myelin gene proteolipid protein 1 (PLP1) have been identified in humans. Attempts to identify a common pathogenic process underlying PMD have been complicated by an incomplete understanding of PLP1 dysfunction and limited access to primary human oligodendrocytes. To address this, we generated panels of human induced pluripotent stem cells (hiPSCs) and hiPSC-derived oligodendrocytes from 12 individuals with mutations spanning the genetic and clinical diversity of PMD-including point mutations and duplication, triplication, and deletion of PLP1-and developed an in vitro platform for molecular and cellular characterization of all 12 mutations simultaneously. We identified individual and shared defects in PLP1 mRNA expression and splicing, oligodendrocyte progenitor development, and oligodendrocyte morphology and capacity for myelination. These observations enabled classification of PMD subgroups by cell-intrinsic phenotypes and identified a subset of mutations for targeted testing of small-molecule modulators of the endoplasmic reticulum stress response, which improved both morphologic and myelination defects. Collectively, these data provide insights into the pathogeneses of a variety of PLP1 mutations and suggest that disparate etiologies of PMD could require specific treatment approaches for subsets of individuals. More broadly, this study demonstrates the versatility of a hiPSC-based panel spanning the mutational heterogeneity within a single disease and establishes a widely applicable platform for genotype-phenotype correlation and drug screening in any human myelin disorder.

Cellular Pathology of Pelizaeus-Merzbacher Disease Involving Chaperones Associated with Endoplasmic Reticulum Stress

Disease-causing mutations in genes encoding membrane proteins may lead to the production of aberrant polypeptides that accumulate in the endoplasmic reticulum (ER). These mutant proteins have detrimental conformational changes or misfolding events, which result in the triggering of the unfolded protein response (UPR). UPR is a cellular pathway that reduces ER stress by generally inhibiting translation, increasing ER chaperones levels, or inducing cell apoptosis in severe ER stress. This process has been implicated in the cellular pathology of many neurological disorders, including Pelizaeus-Merzbacher disease (PMD). PMD is a rare pediatric disorder characterized by the failure in the myelination process of the central nervous system (CNS). PMD is caused by mutations in the PLP1 gene, which encodes a major myelin membrane protein. Severe clinical PMD phenotypes appear to be the result of cell toxicity, due to the accumulation of PLP1 mutant proteins and not due to the lack of functional PLP1. Therefore, it is important to clarify the pathological mechanisms by which the PLP1 mutants negatively impact the myelin-generating cells, called oligodendrocytes, to overcome this devastating disease. This review discusses how PLP1 mutant proteins change protein homeostasis in the ER of oligodendrocytes, especially focusing on the reaction of ER chaperones against the accumulation of PLP1 mutant proteins that cause PMD.

In vivocharacterization of the aspartyl-tRNA synthetase DARS: Homing in on the leukodystrophy HBSL

BACKGROUND

The recently diagnosed leukodystrophy Hypomyelination with Brain stem and Spinal cord involvement and Leg spasticity (HBSL) is caused by mutations of the cytoplasmic aspartyl-tRNA synthetase geneDARS. The physiological role of DARS in translation is to accurately pair aspartate with its cognate tRNA. Clinically, HBSL subjects show a distinct pattern of hypomyelination and develop progressive leg spasticity, variable cognitive impairment and epilepsy. To elucidate the underlying pathomechanism, we comprehensively assessed endogenous DARS expression in mice. Additionally, aiming at creating the first mammalian HBSL model, we genetically engineered and phenotyped mutant mice with a targetedDarslocus.

RESULTS

DARS, although expressed in all organs, shows a distinct expression pattern in the adult brain with little immunoreactivity in macroglia but enrichment in neuronal subpopulations of the hippocampus, cerebellum, and cortex. Within neurons, DARS is mainly located in the cell soma where it co-localizes with other components of the translation machinery. Intriguingly, DARS is also present along neurites and at synapses, where it potentially contributes to local protein synthesis.Dars-null mice are not viable and die before embryonic day 11. Heterozygous mice with only one functionalDarsallele display substantially reduced DARS levels in the brain; yet these mutants show no gross abnormalities, including unchanged motor performance. However, we detected reduced pre-pulse inhibition of the acoustic startle response indicating dysfunction of attentional processing inDars^+/-mice.

CONCLUSIONS

Our results, for the first time, show an in-depth characterization of the DARS tissue distribution in mice, revealing surprisingly little uniformity across brain regions or between the major neural cell types. The complete loss of DARS function is not tolerated in mice suggesting that the identified HBSL mutations in humans retain some residual enzyme activity. The mild phenotype of heterozygousDars-null carriers indicates that even partial restoration of DARS levels would be therapeutically relevant. Despite the fact that they do not resemble the full spectrum of clinical symptoms, the robust pre-pulse inhibition phenotype ofDars^+/-mice will be instrumental for future preclinical therapeutic efficacy studies. In summary, our data is an important contribution to a better understanding of DARS function and HBSL pathology.

The use of targeted genomic capture and massively parallel sequencing in diagnosis of Chinese Leukoencephalopathies

Leukoencephalopathies are diseases with high clinical heterogeneity. In clinical work, it’s difficult for doctors to make a definite etiological diagnosis. Here, we designed a custom probe library which contains the known pathogenic genes reported to be associated with Leukoencephalopathies, and performed targeted gene capture and massively parallel sequencing (MPS) among 49 Chinese patients who has white matter damage as the main imaging changes, and made the validation by Sanger sequencing for the probands’ parents. As result, a total of 40.8% (20/49) of the patients identified pathogenic mutations, including four associated with metachromatic leukodystrophy, three associated with vanishing white matter leukoencephalopathy, three associated with mitochondrial complex I deficiency, one associated with Globoid cell leukodystrophy (or Krabbe diseases), three associated with megalencephalic leukoencephalopathy with subcortical cysts, two associated with Pelizaeus-Merzbacher disease, two associated with X-linked adrenoleukodystrophy, one associated with Zellweger syndrome and one associated with Alexander disease. Targeted capture and MPS enables to identify mutations of all classes causing leukoencephalopathy. Our study combines targeted capture and MPS technology with clinical and genetic diagnosis and highlights its usefulness for rapid and comprehensive genetic testing in the clinical setting. This method will also expand our knowledge of the genetic and clinical spectra of leukoencephalopathy.

The spectrum of leukodystrophies in children: Experience at a tertiary care centre from North India

Objective:

The objective of this study is to retrospectively collect and then describe the clinico-radiographical profile of confirmed cases of leukodystrophy who presented over a 5-year period to a tertiary care teaching hospital in North India.

Materials and Methods:

The case records of 80 confirmed cases of leukodystrophy were reviewed and the cases have been described in terms of their clinical presentation and neuroimaging findings.

Results:

The cases have been grouped into five categories: Hypomyelinating, demyelinating, disorders with vacuolization, cystic, and miscellaneous. The commonest leukodystrophies are megalencephalic leukoencephalopathy with subcortical cysts (MLC), Pelizaeus-Merzbacher disease (PMD), and metachromatic leukodystrophy (MLD). A notable proportion of hypomyelinating disorders were uncharacterized.

Conclusions:

Leukodystrophies at this point of time have no definite cure. They have a progressively downhill clinical course. Early diagnosis is imperative for appropriate genetic counseling. A simplified approach to diagnose common leukodystrophies has also been provided. It is important to develop a registry, which can provide valuable epidemiological data to prioritize research in this field, which has many unanswered questions.

Rare diseases: matching wheelchair users with rare metabolic, neuromuscular or neurological disorders to electric powered indoor/outdoor wheelchairs (EPIOCs)

PURPOSE

To describe the clinical features of electric powered indoor/outdoor wheelchair (EPIOC) users with rare diseases (RD) impacting on EPIOC provision and seating.

METHOD

Retrospective review by a consultant in rehabilitation medicine of electronic and case note records of EPIOC recipients with RDs attending a specialist wheelchair service between June 2007 and September 2008. Data were systematically extracted, entered into a database and analysed under three themes; demographic, diagnostic/clinical (including comorbidity and associated clinical features (ACFs) of the illness/disability) and wheelchair factors.

RESULTS

Fifty-four (27 male) EPIOC users, mean age 37.3 (SD 18.6, range 11-70) with RDs were identified and reviewed a mean of 64 (range 0-131) months after receiving their wheelchair. Diagnoses included 27 types of RDs including Friedreich's ataxia, motor neurone disease, osteogenesis imperfecta, arthrogryposis, cerebellar syndromes and others. Nineteen users had between them 36 comorbidities and 30 users had 44 ACFs likely to influence the prescription. Tilt-in-space was provided to 34 (63%) users and specialised seating to 17 (31%). Four users had between them complex control or interfacing issues.

CONCLUSIONS

The complex and diverse clinical problems of those with RDs present unique challenges to the multiprofessional wheelchair team to maintain successful independent mobility and community living. Implications for Rehabilitation Powered mobility is a major therapeutic tool for those with rare diseases enhancing independence, participation, reducing pain and other clinical features. The challenge for rehabilitation professionals is reconciling the physical disabilities with the individual's need for function and participation whilst allowing for disease progression and/or growth. Powered wheelchair users with rare diseases with a (kypho) scoliosis require a wheelchair system that balances spine stability and movement to maximise residual upper limb and trunk function. The role of specialised seating needs careful consideration in supporting joint derangements and preventing complications such as pressure sores.

Stem cell therapy for white matter disorders: don't forget the microenvironment!

White matter disorders (WMDs) are a major source of handicap at all ages. They often lead to progressive neurological dysfunction and early death. Although causes are highly diverse, WMDs share the property that glia (astrocytes and oligodendrocytes) are among the cells primarily affected, and that myelin is either not formed or lost. Many WMDs might benefit from cell replacement therapies. Successful preclinical studies in rodent models have already led to the first clinical trials in humans using glial or oligodendrocyte progenitor cells aiming at (re)myelination. However, myelin is usually not the only affected structure. Neurons, microglia, and astrocytes are often also affected and are all important partners in creating the right conditions for proper white matter repair. Composition of the extracellular environment is another factor to be considered. Cell transplantation therapies might therefore require inclusion of non-oligodendroglial cell types and target more than only myelin repair. WMD patients would likely benefit from multimodal therapy approaches involving stem cell transplantation and microenvironment-targeting strategies to alter the local environment to a more favorable state for cell replacement. Furthermore most proof-of-concept studies have been performed with human cells in rodent disease models. Since human glial cells show a larger regenerative capacity than their mouse counterparts in the host mouse brain, microenvironmental factors affecting white matter recovery might be overlooked in rodent studies. We would like to stress that cell replacement therapy is a highly promising therapeutic option for WMDs, but a receptive microenvironment is crucial.

Leukodystrophies and genetic leukoencephalopathies in childhood: a national epidemiological study

AIM

To report on the epidemiology of the brain white matter disorders of children identified via a national prospective study.

METHOD

Since 1997 a study of UK children with progressive intellectual and neurological deterioration (PIND) has used the British Paediatric Surveillance Unit system to identify children with progressive neurodegenerative disease. This paper reports on children in the study with brain white matter disorders.

RESULTS

Between May 1997 and November 2014 the PIND study identified 349 children with diagnosed leukodystrophies, giving an estimated UK lifetime risk of 31/million live births. There were 18 specific diseases in the group and relatively large numbers of affected children came from consanguineous Pakistani families. In addition there were 454 children with genetic leukoencephalopathies - in this group there were 38 diseases. 5.8% of children with scan evidence of brain white matter disorders did not receive a specific diagnosis.

INTERPRETATION

These unique prospectively-obtained national data avoid the selection bias inherent in reports from single centres. White matter disorders of the central nervous system comprise more than half of UK paediatric neurodegenerative diseases meeting the PIND criteria. This paper reports the lifetime risk/million live births for the commonest leukodystrophies, providing a basis for comparison with future studies.

Genetics and genomic medicine in Mali: challenges and future perspectives

Genetics and genomic medicine in Mali: challenges and future perspectives.

Deficiency of the alkaline ceramidase ACER3 manifests in early childhood by progressive leukodystrophy

BACKGROUND/AIMS

Leukodystrophies due to abnormal production of myelin cause extensive morbidity in early life; their genetic background is still largely unknown. We aimed at reaching a molecular diagnosis in Ashkenazi-Jewish patients who suffered from developmental regression at 6-13 months, leukodystrophy and peripheral neuropathy.

METHODS

Exome analysis, determination of alkaline ceramidase activity catalysing the conversion of C18:1-ceramide to sphingosine and D-ribo-C12-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD)-phytoceramide to NBD-C12-fatty acid using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and thin layer chromatography, respectively, and sphingolipid analysis in patients' blood by LC-MS/MS.

RESULTS

The patients were homozygous for p.E33G in the ACER3, which encodes a C18:1-alkaline ceramidase and C20:1-alkaline ceramidase. The mutation abolished ACER3 catalytic activity in the patients' cells and failed to restore alkaline ceramidase activity in yeast mutant strain. The levels of ACER3 substrates, C18:1-ceramides and dihydroceramides and C20:1-ceramides and dihydroceramides and other long-chain ceramides and dihydroceramides were markedly increased in the patients' plasma, along with that of complex sphingolipids, including monohexosylceramides and lactosylceramides.

CONCLUSIONS

Homozygosity for the p.E33G mutation in the ACER3 gene results in inactivation of ACER3, leading to the accumulation of various sphingolipids in blood and probably in brain, likely accounting for this new form of childhood leukodystrophy.

Costs of the diagnostic odyssey in children with inherited leukodystrophies

OBJECTIVES

Our objective was to determine the extent of testing and costs solely related to diagnosis (the diagnostic odyssey) in a cohort of children with inherited leukodystrophies.

METHODS

We determined all inpatient and outpatient laboratory testing, including brain MRIs obtained for the purpose of diagnosis, over an 8-year time period in a retrospective population cohort of children with inherited leukodystrophies. Costs were determined from an activity-based cost accounting system and were standardized to 2013 constant US dollars.

RESULTS

Each patient had on average 20 tests (range 2-42 tests), with costs of $4,200 (range $357-$15,611). Diagnostic yield plateaued after 25 tests, and costs increased significantly after 32 tests. Fifty-three percent of patients were diagnosed in 20 or fewer tests, compared with 17% if more than 20 tests were performed.

CONCLUSIONS

Our findings provide details on the amount and costs of testing in children who often undergo a diagnostic odyssey. Our results suggest that diagnostic testing is a relatively modest contributor to the overall health care costs in patients with leukodystrophy, and offer insights into the diagnostic odyssey of children with neurologic impairment.

Participant-driven matchmaking in the genomic era

Whole-genome and whole-exome sequencing are increasingly useful diagnostic tools for novel monogenic conditions. In order to confirm diagnoses made using these technologies, genomic matchmaking-the matching of cases with similar phenotypic and/or genotypic profiles, to narrow the number of candidate genes or ascertain a condition's etiology with greater certainty-is essential. Yet, due to current limitations on the size of matchmaking networks and data sets available to support them, identifying a match can be difficult. We argue that matchmaking efforts led by affected individuals and their families-participant-led efforts-offer a twofold solution to this need, in that participants both have the capacity to access larger networks and to provide more detailed sets of phenotypic and genotypic data. These features of participant-led efforts have the potential to increase the value of matchmaking networks, both in terms of number of matches and in terms of the overall energy of the network. We provide two examples of participant-led matchmaking, and propose a model for scaling these efforts.

Targeted leukodystrophy diagnosis based on charges and yields for testing

Inherited leukodystrophies are a group of neurological disorders with significant morbidity and mortality. Children and their families can experience lengthy diagnostic odysseys; however, there is no data on the charges related to testing for diagnosis in leukodystrophy patients, compared to approaches using next-generation sequencing (NGS). Our objective was to determine charges related to the determination of diagnosis, and overall yield of diagnostic testing, for leukodystrophy patients. We determined and quantified all inpatient and outpatient lab testing, including brain MRIs, obtained for the purpose of diagnosis, in a retrospective population cohort of children with inherited leukodystrophies. Each patient had average charges of $8,231 (range $543-26,437) for diagnostic testing. Overall charges related to diagnosis for the entire cohort was $526,794. A final etiological diagnosis was determined in 34% of patients. In those in whom a specific diagnosis was determined, average time to diagnosis was 1.4 years. If NGS on the entire cohort had been performed instead, charges would have been ∼$359,600 (at $5,800/patient). Alternatively, a two-tier approach consisting of first, biochemical testing (serum very-long chain fatty acids and leukocyte lysosomal enzyme testing), and then with NGS for remaining undiagnosed patients, would have resulted in total cohort charges of $361,309. We have determined the charges directly associated with diagnostic testing in a population cohort of children with leukodystrophy. We conclude that appropriately incorporating NGS into diagnostic algorithms could lower charges; reduce time to diagnosis; and reduce amount of testing.

Emerging treatments for pediatric leukodystrophies

The leukodystrophies are a heterogeneous group of inherited disorders with broad clinical manifestations and variable pathologic mechanisms. Improved diagnostic methods have allowed identification of the underlying cause of these diseases, facilitating identification of their pathologic mechanisms. Clinicians are now able to prioritize treatment strategies and advance research in therapies for specific disorders. Although only a few of these disorders have well-established treatments or therapies, a number are on the verge of clinical trials. As investigators are able to shift care from symptomatic management of disorders to targeted therapeutics, the unmet therapeutic needs could be reduced for these patients.

A clinical approach to the diagnosis of patients with leukodystrophies and genetic leukoencephelopathies

Leukodystrophies (LD) and genetic leukoencephalopathies (gLE) are disorders that result in white matter abnormalities in the central nervous system (CNS). Magnetic resonance (MR) imaging (MRI) has dramatically improved and systematized the diagnosis of LDs and gLEs, and in combination with specific clinical features, such as Addison's disease in Adrenoleukodystrophy or hypodontia in Pol-III related or 4H leukodystrophy, can often resolve a case with a minimum of testing. The diagnostic odyssey for the majority LD and gLE patients, however, remains extensive--many patients will wait nearly a decade for a definitive diagnosis and at least half will remain unresolved. The combination of MRI, careful clinical evaluation and next generation genetic sequencing holds promise for both expediting the diagnostic process and dramatically reducing the number of unresolved cases. Here we present a workflow detailing the Global Leukodystrophy Initiative (GLIA) consensus recommendations for an approach to clinical diagnosis, including salient clinical features suggesting a specific diagnosis, neuroimaging features and molecular genetic testing. We also discuss recommendations on the use of broad-spectrum next-generation sequencing in instances of ambiguous MRI or clinical findings. We conclude with a proposal for systematic trials of genome-wide agnostic testing as a first line diagnostic in LDs and gLEs given the increasing number of genes associated with these disorders.

Consensus statement on preventive and symptomatic care of leukodystrophy patients

Leukodystrophies are inherited disorders whose primary pathophysiology consists of abnormal deposition or progressive disruption of brain myelin. Leukodystrophy patients manifest many of the same symptoms and medical complications despite the wide spectrum of genetic origins. Although no definitive cures exist, all of these conditions are treatable. This report provides the first expert consensus on the recognition and treatment of medical and psychosocial complications associated with leukodystrophies. We include a discussion of serious and potentially preventable medical complications and propose several preventive care strategies. We also outline the need for future research to prioritize clinical needs and subsequently develop, validate, and optimize specific care strategies.

MLC1 protein: a likely link between leukodystrophies and brain channelopathies

Megalencephalic leukoencephalopathy with subcortical cysts (MLCs) disease is a rare inherited, autosomal recessive form of childhood-onset spongiform leukodystrophy characterized by macrocephaly, deterioration of motor functions, epileptic seizures and mental decline. Brain edema, subcortical fluid cysts, myelin and astrocyte vacuolation are the histopathological hallmarks of MLC. Mutations in either the MLC1 gene (>75% of patients) or the GlialCAM gene (<20% of patients) are responsible for the disease. Recently, the GlialCAM adhesion protein was found essential for the membrane expression and function of the chloride channel ClC-2 indicating MLC disease caused by mutation in GlialCAM as the first channelopathy among leukodystrophies. On the contrary, the function of MLC1 protein, which binds GlialCAM, its functional relationship with ClC-2 and the molecular mechanisms underlying MLC1 mutation-induced functional defects are not fully understood yet. The human MLC1 gene encodes a 377-amino acid membrane protein with eight predicted transmembrane domains which shows very low homology with voltage-dependent potassium (K⁺) channel subunits. The high expression of MLC1 in brain astrocytes contacting blood vessels and meninges and brain alterations observed in MLC patients have led to hypothesize a role for MLC1 in the regulation of ion and water homeostasis. Recent studies have shown that MLC1 establishes structural and/or functional interactions with several ion/water channels and transporters and ion channel accessory proteins, and that these interactions are affected by MLC1 mutations causing MLC. Here, we review data on MLC1 functional properties obtained in in vitro and in vivo models and discuss evidence linking the effects of MLC1 mutations to brain channelopathies.

Case definition and classification of leukodystrophies and leukoencephalopathies

OBJECTIVE

An approved definition of the term leukodystrophy does not currently exist. The lack of a precise case definition hampers efforts to study the epidemiology and the relevance of genetic white matter disorders to public health.

METHOD

Thirteen experts at multiple institutions participated in iterative consensus building surveys to achieve definition and classification of disorders as leukodystrophies using a modified Delphi approach.

RESULTS

A case definition for the leukodystrophies was achieved, and a total of 30 disorders were classified under this definition. In addition, a separate set of disorders with heritable white matter abnormalities but not meeting criteria for leukodystrophy, due to presumed primary neuronal involvement and prominent systemic manifestations, was classified as genetic leukoencephalopathies (gLE).

INTERPRETATION

A case definition of leukodystrophies and classification of heritable white matter disorders will permit more detailed epidemiologic studies of these disorders.