Update on leukodystrophies and developing trials

Leukodystrophies are a heterogeneous group of rare genetic disorders primarily affecting the white matter of the central nervous system. These conditions can present a diagnostic challenge, requiring a comprehensive approach that combines clinical evaluation, neuroimaging, metabolic testing, and genetic testing. While MRI is the main tool for diagnosis, advances in molecular diagnostics, particularly whole-exome sequencing, have significantly improved the diagnostic yield. Timely and accurate diagnosis is crucial to guide symptomatic treatment and assess eligibility to participate in clinical trials. Despite no specific cure being available for most leukodystrophies, gene therapy is emerging as a potential treatment avenue, rapidly advancing the therapeutic prospects in leukodystrophies. This review will explore diagnostic and therapeutic strategies for leukodystrophies, with particular emphasis on new trials.

Utility of genetic testing in children with leukodystrophy

BACKGROUND

Leukodystrophies are monogenic disorders primarily affecting the white matter. We aimed to evaluate the utility of genetic testing and time-to-diagnosis in a retrospective cohort of children with suspected leukodystrophy.

METHODS

Medical records of patients who attended the leukodystrophy clinic at the Dana-Dwek Children's Hospital between June 2019 and December 2021 were retrieved. Clinical, molecular, and neuroimaging data were reviewed, and the diagnostic yield was compared across genetic tests.

RESULTS

Sixty-seven patients (Female/Male ratio 35/32) were included. Median age at symptom onset was 9 months (interquartile range (IQR) 3-18 months), and median length of follow-up was 4.75 years (IQR 3-8.5). Time from symptom onset to a confirmed genetic diagnosis was 15months (IQR 11-30). Pathogenic variants were identified in 60/67 (89.6%) patients; classic leukodystrophy (55/67, 82.1%), leukodystrophy mimics (5/67, 7.5%). Seven patients (10.4%) remained undiagnosed. Exome sequencing showed the highest diagnostic yield (34/41, 82.9%), followed by single-gene sequencing (13/24, 54%), targeted panels (3/9, 33.3%) and chromosomal microarray (2/25, 8%). Familial pathogenic variant testing confirmed the diagnosis in 7/7 patients. A comparison between patients who presented before (n = 31) and after (n = 21) next-generation sequencing (NGS) became clinically available in Israel revealed that the time-to-diagnosis was shorter in the latter group with a median of 12months (IQR 3.5-18.5) vs. a median of 19 months (IQR 13-51) (p = 0.005).

CONCLUSIONS

NGS carries the highest diagnostic yield in children with suspected leukodystrophy. Access to advanced sequencing technologies accelerates speed to diagnosis, which is increasingly crucial as targeted treatments become available.

Case report: Biallelic variants in POLR3B gene lead to 4H leukodystrophy from the study of brother and sister

INTRODUCTION

4H leukodystrophy, one of POLR3-related leukodystrophy, is a rare hereditary brain white matter disease caused by the pathogenic biallelic variations in POLR3A, POLR3B, or POLR1C. Hypomyelination, hypodontia, and hypogonadotropic hypogonadism is mainly presented in patients with 4H leukodystrophy.

PATIENT CONCERNS

Here, we reported the brother and the sister with new compound heterozygous (c.1615G>T and c.165-167del) with various degrees of phenotypes including dysbasia, myopia, dental abnormal, and hypogonadotropic hypogonadism.

DIAGNOSIS

The brother and sister were diagnosed with 4H leukodystrophy.

INTERVENTIONS

Gonadotrophins treatment of the brother could significantly improve the development of secondary sexual characteristics and genitalia.

OUTCOMES

This study showed that the same genotype of POLR3B may have variable clinical phenotypes in the brother and sister.

CONCLUSION

The exploration of molecular functions and genetic counseling are crucial for further diagnosis and treatment of POLR3-related leukodystrophy.

AGC1 Deficiency: Pathology and Molecular and Cellular Mechanisms of the Disease

AGC1/Aralar/Slc25a12 is the mitochondrial carrier of aspartate-glutamate, the regulatory component of the NADH malate-aspartate shuttle (MAS) that transfers cytosolic redox power to neuronal mitochondria. The deficiency in AGC1/Aralar leads to the human rare disease named "early infantile epileptic encephalopathy 39" (EIEE 39, OMIM # 612949) characterized by epilepsy, hypotonia, arrested psychomotor neurodevelopment, hypo myelination and a drastic drop in brain aspartate (Asp) and N-acetylaspartate (NAA). Current evidence suggest that neurons are the main brain cell type expressing Aralar. However, paradoxically, glial functions such as myelin and Glutamine (Gln) synthesis are markedly impaired in AGC1 deficiency. Herein, we discuss the role of the AGC1/Aralar-MAS pathway in neuronal functions such as Asp and NAA synthesis, lactate use, respiration on glucose, glutamate (Glu) oxidation and other neurometabolic aspects. The possible mechanism triggering the pathophysiological findings in AGC1 deficiency, such as epilepsy and postnatal hypomyelination observed in humans and mice, are also included. Many of these mechanisms arise from findings in the aralar-KO mice model that extensively recapitulate the human disease including the astroglial failure to synthesize Gln and the dopamine (DA) mishandling in the nigrostriatal system. Epilepsy and DA mishandling are a direct consequence of the metabolic defect in neurons due to AGC1/Aralar deficiency. However, the deficits in myelin and Gln synthesis may be a consequence of neuronal affectation or a direct effect of AGC1/Aralar deficiency in glial cells. Further research is needed to clarify this question and delineate the transcellular metabolic fluxes that control brain functions. Finally, we discuss therapeutic approaches successfully used in AGC1-deficient patients and mice.

[Hypomyelinating leukodystrophy type 6. Clinical and neuroimaging key features in the detection of a new case]

INTRODUCTION

Hypomyelinating leukodystrophy-6 is a rare and early onset neurodegenerative disease which entails a clinical pattern of pyramidal-extrapyramidal and cerebellar involvement and it comes with a neuroimaging consisting of hypomielination, cerebellar hypoplasia and specific abnormalities in basal ganglia, particularly the absence or nearly absence of putamen and the possible loss of caudate's volume. It is due to an alteration in tubulin and it is determined by mutations in heterocygosis in TUBB4A gene, showing complete penetrance.

CASE REPORT

An 8-year-old child with history of delayed motor development, tremor, dysathria, ataxia, nystagmus, cognitive deficit and dystonia with pattern of hypomielination, vermis hypoplasia and absence of putamen. These findings, although distinctive, had been underestimated in previous evaluations and their detection determined the analyse and identification of a pathogenic variant in TUBB4A gene.

CONCLUSIONS

Progressive deterioration leads the patient to total dependence or death in infancy or youth and there is no specific treatment capable of modifying its natural course.

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.

[Hypomyelination with atrophy of the basal ganglia and cerebellum. Contribution of two new cases to a recently reported entity]

INTRODUCTION

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a rare condition that has only recently been reported. Here we present two new cases belonging to the same family.

CASE REPORTS

Case 1: 17-month-old boy with severe underdevelopment in all areas, absence of language and eye contact. The examination revealed microcephaly with spastic tetraparesis. A magnetic resonance imaging scan showed predominantly vermian atrophy of the cerebellum with loss of volume of both nuclei of the putamen and the head of the caudate, and a pattern of hypomyelination of the white matter. Electromyography recording highlighted the presence of a predominantly motor pattern of chronic polyneuropathy. Homovallinic acid and 5-hydroxyindoleacetic acid values were lower than usual. Treatment with levodopa/carbidopa was not effective. Case 2: 11-month-old girl, the sister of the boy in the previous case. The patient presented severe underdevelopment in all areas and microcephaly with spastic tetraparesis was detected in the clinical examination. Magnetic resonance imaging of the head showed findings that could be superimposed upon those of the brother, with hypomyelination, cerebellar atrophy and involvement of the putamen and both caudates; electromyography findings were consistent with motor polyneuropathy of a demyelinating nature. Homovallinic acid and 5-hydroxyindoleacetic acid values in cerebrospinal fluid were lower than usual. Treatment with levodopa/carbidopa was ineffective.

CONCLUSIONS

These two new cases help characterise this condition better and reinforce the hypothesis of the genetic origin of the syndrome, given that the two cases occurred in the same family.

[MRI in the diagnosis of hereditary leukoencephalopathies (review)]

The review addresses MR imaging of hereditary leukoencephalopathies (HL) as one of the most urgent problems of modern neurology and neuroradiology. HL is a group of rare human diseases that occur with a primary brain white matter lesions. Modern theoretical and methodological approaches for MRI of patients with hereditary leukoencephalopathies and data analysis are discussed. The authors demonstrate that MRI plays the important role in the diagnosis and differential diagnosis of HL, in-vivo imaging of structural changes in the brain that are correlated with pathogenetic mechanisms of these diseases.

Leukodystrophies

Leukodystrophies comprise a broad group of progressive, inherited disorders affecting mainly myelin. They often present after a variable period of normalcy with a variety of neurologic problems. Though the ultimate diagnosis is not found in many patients with leukodystrophies, distinctive features unique to them aid in diagnosis, treatment and prognostication. The clinical characteristics, etiologies, diagnostic testing and treatment options are reviewed in detail for some of the major leukodystrophies: X-linked adrenoleukodystrophy, Krabbe disease, metachromatic leukodystrophy, Pelizaeus-Merzbacher disease, Alexander disease, Canavan disease, megalencephalic leukoencephalopathy with subcortical cysts and vanishing white matter disease.

A Japanese adult case of megalencephalic leukoencephalopathy with subcortical cysts with a good long-term prognosis

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a recently recognized neurological disease, and mutations in the MLC1 gene have been identified as the cause of the disorder. A 54-year-old Japanese woman with macrocephaly presented with progressive mental decline, gait disturbance due to spasticity and ataxia, and choreoathetotic movement in the left upper extremity. Brain magnetic resonance imaging (MRI) revealed characteristic subcortical cysts in addition to diffuse white matter involvement. Genetic analysis of the MLC1 gene identified an S93L mutation in a homozygous state. This case is particularly valuable because of the lack of knowledge on the long-term prognosis of MLC.

[Leucodystrophy induced by late onset 3-hydroxy-3-methylglutaric aciduria]

3-Hydroxy-3-methylglutaric aciduria is a rare disorder of organic acid metabolism caused by 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency. The disorder was common in neonatal or infant period. Here a case of late onset 3-hydroxy-3-methylglutaric aciduria complicated by leucodystrophy was reported. The patient was a 7-year-old boy. He presented with progressive headache, drowsiness and vomiting. Hepatic lesions, ketosis and leucopenia were found. Symmetrical diffused leucodystrophy was shown by MRI. Blood levels of isovalerylcarnitine and acetylcarnitine increased significantly. Urinary levels of 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-hydroxyglutaric acids and 3-methyl-crotonylglycine increased significantly. Symptoms were released by intravenous infusion of L-carnitine and glucose. After treatment for 6 months, urinary levels of 3-hydroxy-3-methylglutaric aciduria decreased in the boy and his health improved.

A novel duplication confirms the involvement of 5q23.2 in autosomal dominant leukodystrophy

OBJECTIVE

To identify the underlying locus and disease-causing mutation for adult-onset autosomal dominant leukodystrophy (ADLD).

DESIGN

Previously, an adult-onset ADLD locus on chromosome 5q23 was mapped between markers D5S1495 and CTT/CCT15. This region contains 13 known and putative candidate genes. A 2-point linkage analysis confirmed linkage of a large multigenerational French Canadian family to chromosome 5q23. In addition, screening of the 13 genes within the candidate interval as well as 5 neighboring genes was completed, followed by comparative genomic hybridization.

SUBJECTS

A multigenerational French Canadian family with ADLD mimicking progressive multiple sclerosis was identified and studied. Eight affected family members were available for the study and presented with autonomic dysfunction as well as upper motorneuron signs affecting gait.

RESULTS

The thorough candidate gene approach did not identify any mutation. Consequently, a whole-chromosome comparative genomic hybridization for chromosome 5 identified a 280-kilobase duplication within the chromosomal band 5q23.2 in 2 affected individuals. This duplication contains 3 genes: LMNB1, FLJ36242, and MARCH3.

CONCLUSION

We have identified a novel duplication on chromosomal band 5q23.2 in a French Canadian family with ADLD that supports the implication of duplicated LMNB1 as the disease-causing mutation. However, additional functional studies of lamin B1 overexpression are necessary to elucidate the involvement of lamin B1 in myelination and in degenerative disorders such as ADLD and multiple sclerosis.

Classification of childhood white matter disorders using proton MR spectroscopic imaging

BACKGROUND AND PURPOSE

Childhood white matter disorders often show similar MR imaging signal-intensity changes, despite different underlying pathophysiologies. The purpose of this study was to determine if proton MR spectroscopic imaging ((1)H-MRSI) may help identify tissue pathophysiology in patients with leukoencephalopathies.

MATERIALS AND METHODS

Seventy patients (mean age, 6; range, 0.66-17 years) were prospectively examined by (1)H-MRSI; a diagnosis of leukoencephalopathy due to known genetic defects leading to lack of formation, breakdown of myelin, or loss of white matter tissue attenuation (rarefaction) was made in 47 patients. The diagnosis remained undefined (UL) in 23 patients. Patients with definite diagnoses were assigned (on the basis of known pathophysiology) to 3 groups corresponding to hypomyelination, white matter rarefaction, and demyelination. Choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) signals from 6 white matter regions and their intra- and intervoxel (relative to gray matter) ratios were measured. Analysis of variance was performed by diagnosis and by pathophysiology group. Stepwise linear discriminant analysis was performed to construct a model to predict pathophysiology on the basis of (1)H-MRSI, and was applied to the UL group.

RESULTS

Analysis of variance by diagnosis showed 3 main metabolic patterns. Analysis of variance by pathophysiology showed significant differences for Cho/NAA (P < .001), Cho/Cr (P < .004), and NAA/Cr (P < .002). Accuracy of the linear discriminant analysis model was 75%, with Cho/Cr and NAA/Cr being the best parameters for classification. On the basis of the linear discriminant analysis model, 61% of the subjects in the UL group were classified as hypomyelinating.

CONCLUSION

(1)H-MRSI provides information on tissue pathophysiology and may, therefore, be a valuable tool in the evaluation of patients with leukoencephalopathies.

Increased level of N-acetylaspartylglutamate (NAAG) in the CSF of a patient with Pelizaeus-Merzbacher-like disease due to mutation in the GJA12 gene

Autosomal recessive Pelizaeus-Merzbacher-like disease 1 (PMLD1) is a hypomyelinating disorder of the central nervous system (CNS) with virtually identical phenotype to Pelizaeus-Merzbacher disease (PMD). PMLD1 is caused by mutations in GJA12 gene, PMD is due to mutations in PLP1 gene. Elevated levels of N-acetylaspartylglutamate (NAAG), the most abundant peptide neuromodulator in the human brain, have been recently reported in cerebral spinal fluid (CSF) of patients with PMD. Using capillary electrophoresis, we analyzed for the first time, the CSF from a girl with PMLD1 and detected high concentrations of NAAG. This finding confirms the hypothesis that NAAG may be involved in myelination-related processes and can be considered as a useful diagnostic marker not only for patients with the PLP1 related disorder, but also in those with Pelizaeus-Merzbacher like hypomyelinating disease due to other defined genetic causes, such as PMLD1.

Leukoencephalopathies associated with inborn errors of metabolism in adults

The discovery of a leukoencephalopathy is a frequent situation in neurological practice and the diagnostic approach is often difficult given the numerous possible aetiologies, which include multiple acquired causes and genetic diseases including inborn errors of metabolism (IEMs). It is now clear that IEMs can have their clinical onset from early infancy until late adulthood. These diseases are particularly important to recognize because specific treatments often exist. In this review, illustrated by personal observations, we give an overview of late-onset leukoencephalopathies caused by IEMs.

Phenotypic characterization of hypomyelination and congenital cataract

OBJECTIVE

To define the clinical and laboratory findings in a novel autosomal recessive white matter disorder called hypomyelination and congenital cataract, recently found to be caused by a deficiency of a membrane protein, hyccin, encoded by the DRCTNNB1A gene located on chromosome 7p21.3-p15.3.

METHODS

We performed neurological examination, neurophysiological, neuroimaging, and neuropathological studies on sural nerve biopsy in 10 hypomyelination and congenital cataract patients from 5 unrelated families.

RESULTS

The clinical picture was characterized by bilateral congenital cataract, developmental delay, and slowly progressive neurological impairment with spasticity, cerebellar ataxia, and mild-to-moderate mental retardation. Neurophysiological studies showed a slightly to markedly slowed motor nerve conduction velocity in 9 of 10 patients, and multimodal evoked potentials indicated increased central conduction times. Neuroimaging studies demonstrated a diffuse supratentorial hypomyelination, with in some patients, additional areas of more prominent signal change in the frontal region. Sural nerve biopsy showed a slight-to-severe reduction in myelinated fiber density, with several axons surrounded by a thin myelin sheath or devoid of myelin.

INTERPRETATION

Hypomyelination and congenital cataract is a novel autosomal recessive white matter disorder characterized by the unique association of congenital cataract and hypomyelination of the central and peripheral nervous system.

Le syndrome CACH/VWM et les leucodystrophies liées à des mutations EIF2B

A new leukoencephalopathy, the CACH syndrome (Childhood Ataxia with Central nervous system Hypomyelination) or VWM (Vanishing White Matter) was identified on clinical and MRI criteria. Classically, this disease is characterized by (1) an onset between 2 and 5 years of age, with a cerebello-spastic syndrome exacerbated by episodes of fever or head trauma leading to death after 5 to 10 years of disease evolution, (2) a diffuse involvement of the white matter on cerebral MRI with a CSF-like signal intensity (cavitation), (3) a recessive autosomal mode of inheritance, (4) neuropathologic findings consistent with a cavitating orthochromatic leukodystrophy with increased number of oligodendrocytes with sometimes "foamy" aspect. A total of 148 cases have been reported so far. This disease is linked to mutations in the five EIF2B genes encoding the five subunits of the eukaryotic initiation factor 2B (eIF2B), involved in the protein synthesis and its regulation under cellular stresses. Clinical symptoms are variable, from fatale infantile forms (Cree leukoencephalopathy) and congenital forms associated with extra-neurological affections, to juvenile and adult forms (ovarioleukodystrophy) characterized by cognitive and behaviour dysfunctions and by a slow progression of the disease, leading to the term of eIF2B-related leukoencephalopathies. Prevalence of these remains unknown. Diagnosis lays on the detection of EIF2B mutations, affecting predominantly the EIF2B5 gene. A decrease in the intrinsic activity of the eIF2B factor (the guanine exchange activity, GEF) in lymphoblasts from patients seems to have a diagnostic value. The patho-physiology of the disease would involve a deficiency in astrocytes maturation leading to an increased susceptibility of the white matter to cellular stress. No specific treatment exists except the "prevention" of cellular stress. Corticosteroids sometimes proved to be useful in acute phases. Prognosis seems to correlate with the age of onset, the earliest forms being more severe.

[Leukoencephalopathy with vanishing white matter: A case report]

INTRODUCTION

Leukoencephalopathy with vanishing white matter is an autosomal recessive hereditary disease that was first reported in 1997. Some time later the genetic anomalies responsible for the disease were identified, these being different mutations in any of the five genes that code for the five subunits of the translation initiation factor, eIF2B. Since then, the clinical spectrum of this condition has proved to be much broader and far more frequent than was initially believed. We report on a case of the classical clinical form, which is to our knowledge the first to be published in Spain to date.

CASE REPORT

A 5-year-old female who presented gait instability that recently got worse following a mild traumatic head injury. The examination revealed overall cerebellar ataxia and generalised spasticity. Magnetic resonance imaging (MRI) showed diffuse and symmetrical involvement of the white matter of the brain with the presence of cavities in which the signal intensity and the proton spectrum were similar to those of cerebrospinal fluid. The genetic study revealed a mutation of the gene that codes for eIF2B-epsilon.

CONCLUSIONS

A suggestive MRI scan, even in an atypical presentation, would be enough to rule out a mutation of the genes that code for eIF2B. This would make it possible to reach an early diagnosis of this disease, which is probably more prevalent than is currently thought. This would allow genetic counselling to be conducted and would help to establish a genotype-phenotype correlate that would also make it possible to offer an estimated prognosis.

Global brain dysmyelination with above-average verbal skills in 18q- syndrome with a 17 Mb terminal deletion

BACKGROUND

Patients with the karyotypic finding of a terminal deletion in the long arm of chromosome 18 (18q- syndrome) commonly display cerebral dysmyelination and developmental delay. To our knowledge, all reported cases characterized by molecular analysis who had no mental retardation as confirmed by neuropsychological testing had a chromosomal breakpoint within the two most distal bands, 18q22 or 18q23, leading to a deletion of 16 Mb or less.

AIMS OF THE STUDY

It was the aim of this study to improve the karyotype-phenotype correlation in 18q- syndrome by thoroughly analyzing the deletion size and the mental and radiologic status in a 23-year-old woman with a terminal 18q deletion. We performed cytogenetic and molecular cytogenetic analysis, brain MRI, and extended neuropsychological testing.

RESULTS

Molecular karyotyping revealed a 17 Mb deletion of terminal 18q with a breakpoint in 18q21.33 and no evidence for mosaicism. While brain MRI demonstrated severe global dysmyelination, the patient showed a neuropsychological pattern that allowed for normal psychosocial and job achievement. After delayed development in childhood, the patient caught up during puberty and showed normal verbal intelligence and skills at 23 years. However, visual, visual-spatial, visual-constructional, and executive functions were found to be severely impaired.

CONCLUSION

Here, we present a patient with one of the largest terminal 18q deletions reported in an individual without obvious mental retardation. Our analysis extends the phenotypic spectrum for individuals with breakpoints in 18q21.33. In addition, this study highlights the fact that severe global dysmyelination may not be associated with general cognitive deficits.

Leukodystrophies: clinical and genetic aspects

The leukodystrophies comprise an ever-expanding group of rare central nervous system disorders with defined clinical, pathological, and genetic characteristics. The broader term, leukoencephalopathy, is applied to all brain white matter diseases, whether their molecular cause is known. Magnetic resonance imaging has helped to elucidate new forms of leukodystrophy as well as to permit longitudinal studies of disease progression. The white matter abnormality may appear similar in different forms of leukodystrophy so that in most cases, further studies such as magnetic resonance spectroscopy, tissue biopsies, enzyme studies, and molecular DNA analyses are needed to pinpoint the specific diagnosis. The primary inherited leukoencephalopathies include dysmyelinating, hypomyelinative, and vacuolating forms. Metabolic and vascular causes account for most of the secondary forms, but other inherited syndromes are recognized that have their onset in childhood or adult life and are characterized by distinctive clinical and neuropathologic features. This review discusses some of the mechanisms that have been proposed to explain deficiencies of myelin and the molecular genetic bases underlying these disorders.

Vanishing white matter disease with periodic (paroxysmal) hemiparesis

Vanishing white matter disease is a chronically progressive leukodystrophy with periods of acute deterioration after head trauma and febrile illness. This report describes a child with genetically and clinically confirmed vanishing white matter disease exhibiting frequent episodes of right-sided hemiplegia, aphasia, and headache resolving fully within hours to days. This report describes a case of this condition presenting with episodes of hemiparesis with full discovery to baseline. Some possible mechanisms explaining this unusual presentation are provided.

Megalencephalic leukoencephalopathy with subcortical cysts: an update and extended mutation analysis of MLC1

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an autosomal recessive cerebral white matter disorder in children. This disease is histopathologically characterized by myelin splitting and intramyelinic vacuole formation. MLC is caused by mutations in the gene MLC1, which encodes a novel protein, MLC1. Since the first report, 50 mutations in this gene have been found. Mutations occur throughout the entire coding region and include all different types: 11 splice-site mutations; one nonsense mutation; 24 missense mutations; and 14 deletions and insertions. Until now, six polymorphisms within the coding sequence of MLC1 had been reported. In about 20% of the patients with a typical clinical and MRI picture, no mutations in the MLC1 gene are found. Several of the families, in which no mutations are found, also do not show linkage with the MLC1 locus, which suggests a second gene involved in MLC. The absence of mutations may also be the consequence of performing standard mutation analysis that can miss heterozygous deletions, mutations in the promoter, 3' and 5' untranslated regions (UTRs), and intron mutations, which may influence the amino acid composition of the end product. In this work we describe 13 novel mutations, including those found with extended mutation analysis on MLC patients. This study shows that extended mutation analysis is a valuable tool to identify at least some of the missing mutations. Therefore, we suggest extended mutation analysis for the MLC1 gene, if no mutations are found during standard analysis.

GJA12 mutations in children with recessive hypomyelinating leukoencephalopathy

BACKGROUND

Pelizaeus-Merzbacher-like disease (PMLD) is an inherited hypomyelinating leukoencephalopathy with onset in early infancy. Like Pelizaeus-Merzbacher disease (PMD), PMLD is characterized clinically by nystagmus, cerebellar ataxia, and spasticity, due to a permanent lack of myelin deposition in the brain. Mutations in the GJA12 gene, encoding connexin 47 (Cx47), were recently reported in five children with autosomal recessive PMLD.

OBJECTIVES

To evaluate the impact of mutations in the GJA12 gene in, and define the clinical and neuroimaging features of, autosomal recessive PMLD.

RESULTS

The authors screened for GJA12 mutations in 10 additional PMLD families originating from Italy, Pakistan, and Saudi Arabia. Three novel homozygous GJA12 mutations were identified in 12 mutant cases distributed in 3 of 10 families. The mutations segregated with the disease according to an autosomal recessive trait and included one missense (G236S) and two nonsense (L281fs285X and P131fs144X) changes.

CONCLUSIONS

The identification of homozygous mutations predicting the synthesis of aberrant and truncated polypeptides, and their tight segregation with the disease in very large families, clearly demonstrate that the loss of Cx47 function is the cause of the disease. The phenotype of GJA12-related Pelizaeus-Merzbacher-like disease is fairly homogeneous and similar to that of Pelizaeus-Merzbacher disease. However, slower progression of symptoms, greater preservation of cognitive functions, and partial myelination of corticospinal tracts at MRI were distinctive features, which could help in the differential diagnosis.

Nonprogressive familial leukoencephalopathy with porencephalic cyst and focal seizures

Two siblings with a similar white-matter disease but different clinical symptoms are described. The first sibling suffers from nonprogressive spastic hemiparesis secondary to a congenital periventricular porencephalic cyst. Her brother has focal epilepsy. On magnetic resonance imaging, both patients show diffuse white-matter involvement predominantly of the posterior periventricular area. We suggest that this is a familial white-matter disorder with minimal symptoms and no progression in early childhood.

TNF-Rezeptor-assoziiertes periodisches Syndrom

Tumour necrosis factor receptor-associated periodic syndrome (TRAPS), a rare autosomal dominant disorder, is characterised by recurrent attacks of fever, myalgias, and abdominal pain. However, manifestations in the central nervous system are hardly known. We describe a family in which one of three affected members developed central nervous system symptoms. First diagnosed as multiple sclerosis (MS), the demyelinisation seems to be a feature of TRAPS rather than MS. The syndrome is discussed as a rare differential diagnosis of MS.

Diffusion-weighted MR imaging in leukodystrophies

Leukodystrophies are genetically determined metabolic diseases, in which the underlying biochemical abnormality interferes with the normal build-up and/or maintenance of myelin, which leads to hypo- (or arrested) myelination, or dysmyelination with resultant demyelination. Although conventional magnetic resonance imaging has significantly contributed to recent progress in the diagnostic work-up of these diseases, diffusion-weighted imaging has the potential to further improve our understanding of underlying pathological processes and their dynamics through the assessment of normal and abnormal diffusion properties of cerebral white matter. Evaluation of conventional diffusion-weighted and ADC map images allows the detection of major diffusion abnormalities and the identification of various edema types, of which the so-called myelin edema is particularly relevant to leukodystrophies. Depending on the nature of histopathological changes, stage and progression gradient of diseases, various diffusion-weighted imaging patterns may be seen in leukodystrophies. Absent or low-grade myelin edema is found in mucopolysaccharidoses, GM gangliosidoses, Zellweger disease, adrenomyeloneuropathy, L-2-hydroxyglutaric aciduria, non-ketotic hyperglycinemia, classical phenylketonuria, Van der Knaap disease and the vanishing white matter, medium grade myelin edema in metachromatic leukodystrophy, X-linked adrenoleukodystrophy and HMG coenzyme lyase deficiency and high grade edema in Krabbe disease, Canavan disease, hyperhomocystinemias, maple syrup urine disease and leukodystrophy with brainstem and spinal cord involvement and high lactate.

Hereditäre motorische und sensorische Neuropathie (HMSN) mit Hypertrophie der Cauda equina und demyelinisierenden Läsionen der weißen Substanz

Hereditary motor and sensory neuropathy (HMSN) is thought to almost exclusively affect the peripheral nervous system. We report the case of a 48-year-old patient with a longstanding history of HMSN type I who developed signs and symptoms of a cauda equina compression and of a central nervous system relapsing-remitting demyelinating white matter disease. Gross enlargement of the cauda equina fibers was detected by MR imaging of the lumbar spine. Cranial MR imaging revealed demyelinating white matter lesions. This case suggests that peripheral neuropathic mechanisms may also affect the central myelin in HMSN type I.

Leukodystrophies: Indian scenario

The leukodystrophies are familial disorders with onset usually in infancy or childhood. The clinical features consist of motor dysfunction with varying degree of cognitive decline. Magnetic Resonance Imaging (MRI) has helped to identify and characterize these disorders. In some leukodystrophies, biochemical enzymatic and genetic defects have been identified. The commonest leukodystrophy seen in India is Megalencephalic Leukodystrophy with subcortical cysts. The essential features consist of large head, mild pyramidal and cerebellar dysfunction, and occasional seizures. MRI studies show extensive white matter changes with temporal cysts. It is common in the Agarwal community in India. An identical mutation in exon 2 of the MLC 1 gene has been identified in this community suggesting a founder effect.

Tools for diagnosis of leukodystrophies and other disorders presenting with white matter disease

Advances in biochemical techniques, molecular genetics, and neuroimaging, particularly magnetic resonance imaging, have made possible the diagnosis of a significant proportion of leukodystrophies. A specific diagnosis allows the physician to give prognostic information, monitor for known complications, and ultimately may allow disease specific therapeutics. The purpose of this review is to familiarize the reader with pertinent tools in the diagnosis of leukodystrophies and other white matter disorders that may present with white matter disease. The first section discusses conditions that may mimic leukodystrophy and how to exclude them. Although not meant to be an exhaustive summary, several key disorders and their clinical, biochemical, and neuroimaging features are presented. The second section focuses on classically described leukodystrophies and their diagnosis. Finally, a third section provides a diagnostic algorithm to help the clinician in the diagnosis of the patient with leukodystrophy.

Megalencephalic leukoencephalopathy with subcortical cysts in two siblings owing to two novel mutations: case reports and review of the literature

Megalencephalic leukoencephalopathy with subcortical cysts is a rare leukodystrophy characterized by macrocephaly and a slowly progressive clinical course marked by spasticity and cognitive decline. We report two full siblings with neuroimaging studies and clinical courses typical for megalencephalic leukoencephalopathy with subcortical cysts, in whom a pair of novel mutations in the MLC1 gene was identified. We review the current knowledge of this disorder in relation to the patients reported.

Decreased guanine nucleotide exchange factor activity in eIF2B-mutated patients

Mutations in each of the five eucaryotic initiation factor 2B (eIF2B) subunits have been found in leukodystrophies of various severity: Cree leukoencephalopathy, childhood ataxia with central hypomyelination/leukodystrophy with vanishing white matter and ovarioleukodystrophy. A continuum was observed from fatal infantile forms to adult forms without neurological deterioration. Disease severity was found to correlate with the age at disease onset and the specific amino-acid substitution. In order to analyze the functional consequences of eIF2B mutations, we measured the guanine nucleotide exchange factor (GEF) activity of eIF2B in transformed lymphocytes from 30 affected patients carrying mutations in eIF2B compared to 10 unaffected heterozygotes and 22 controls without eIF2B mutations. A significant decrease of 20-70% in GEF activity was observed in all mutated cells. The severity of this decrement of GEF activity correlated with age at onset of the disease. These results suggest that a deficiency in GEF activity underlies the encephalopathy associated eIF2B-related disease. Our study demonstrates that the evaluation of the GEF activity in transformed lymphocytes represents an interesting alternative test to the systematic screening of the five EIF2B genes. This relevant cellular model may also be used to test the functional impact of different molecules on the GEF activity for future therapeutic strategies.

Megalencephalic leukoencephalopathy with subcortical cysts

Megalencephalic leukoencephalopathy with subcortical cysts is a rare disease first described in 1995. It is characterized by macrocephaly and early onset white matter degeneration. We report two siblings who were diagnosed to have this disease. This disease must be included in differential diagnosis of macrocephaly with early onset leukoencephalopathy.

Familial multiple sclerosis and other inherited disorders of the white matter

BACKGROUND

An objective demonstration of lesions disseminated in time and space remains the core of the last revision of diagnostic criteria for multiple sclerosis (MS), but this update is now empowered by a weighted use of magnetic resonance imaging (MRI), which results in an earlier and more unambiguous diagnosis ("MS," "not MS," or "possible MS"). Nevertheless, the exclusion of other entities still remains an integral element of the diagnostic process.

REVIEW SUMMARY

Exclusion of genetic disorders can be challenging in some cases with familial recurrence of MS, particularly when the transmission is mimicking a mendelian or a maternal pattern of inheritance. Vice versa, many forms of mendelian leukodystrophies and leukoencephalopathies present with juvenile or adult onset, progressive or relapsing-remitting courses, intrafamilial phenotypic heterogeneity and MRI signs of multifocal white matter (WM) pathology, features potentially leading to a temporary confusion with MS. With the recent availability of disease modifying medications in MS, the development of specific molecular therapies in inherited WM disorders, and the general recognition of the effectiveness of early treatments, the accuracy of initial diagnostic assessment has become critical.

CONCLUSION

Considering the importance of disease specific treatments, here we review the major characteristics of familial MS and some of the inheritable diseases of the WM. Although no direct genetic link between MS and these WM abnormalities is known, molecular data from the field of rare genetic disorders may also provide some experimental paradigms to a further exploration of MS.

The effect of genotype on the natural history of eIF2B-related leukodystrophies

BACKGROUND

Recessive mutations in the five eucaryotic initiation factor 2B (eIF2B) subunits have been found in leukodystrophies of variable age at onset and severity.

OBJECTIVES

To evaluate the clinical spectrum of eIF2B-related disorders and search for a phenotype-genotype correlation.

METHODS

Ninety-three individuals (78 families) with an undetermined leukodystrophy were selected on MRI-based criteria of childhood ataxia with central hypomyelination/vanishing white matter (CACH/VWM) for EIF2B genes analysis.

RESULTS

Eighty-nine percent of individuals with MRI criteria of CACH/VWM have a mutation in one of the eIF2B beta to epsilon subunits. For 83 individuals (68 families), 46 distinct mutations (90% missense) in four of the five eIF2B subunits (beta, gamma, delta, epsilon) were identified. Sixty-four percent were in the epsilon subunit, a R113H substitution was found in 71% of eIF2B epsilon-mutated families. A large clinical spectrum was observed from rapidly fatal infantile to asymptomatic adult forms. Disease severity was correlated with age at onset (p < 0.0001) but not with the type of the mutated subunit nor with the position of the mutation within the protein. Mutations R113H in the epsilon subunit and E213G in the beta subunit were significantly associated with milder forms.

CONCLUSIONS

The degree of eIF2B dysfunction, which is involved in the regulation of protein synthesis during cellular stress, may play a role in the clinical expression of eIF2B-related disorders.

Neuroimaging in leukodystrophies

The application of techniques based on in vivo magnetic resonance to the study of leukodystrophies is evaluated. Magnetic resonance imaging (MRI), the most important neuroimaging modality for patients with leukodystrophies, has proven invaluable for the detection of the extent and etiology of white-matter involvement, diagnosis, and monitoring of disease progression. Proton magnetic resonance spectroscopy, which can detect several brain metabolites, including those related to axonal function and myelination, can provide additional diagnostic and prognostic information and, in some cases, allows a rare insight into the biochemical pathology of leukodystrophies. The potential of other advanced magnetic resonance techniques, including diffusion tensor imaging, magnetization transfer contrast, and molecular imaging, is also discussed. In the future, anatomic and physiologic magnetic resonance techniques are expected to be integrated into a single examination that will provide a detailed characterization of white-matter diseases in children.

Megalencephalic leukoencephalopathy with subcortical cysts

Megalencephalic leukocncephalopathy is rare disorder seen in India in patient belonging to Agarwal community. Many of the patients may have a mild clinical course with gradual worsening of neurological disability. A case is being reported who was followed for 17 years and paradoxically showed radiological and clinical improvement.

The latest on leukodystrophies

PURPOSE OF REVIEW

Important advances in our understanding of genetic disorders of the white matter have been made and are discussed here.

RECENT FINDINGS

It has recently been discovered that mutations in the genes encoding the five subunits of eukaryocytic initiation factor 2B (eIF2B) are the cause of vanishing white-matter disease/childhood ataxia with central hypomyelination syndrome. The extension of the clinical features of the eIF2B-related disorders to encompass both infant- and adult-onset disorders is discussed. New clinico-imaging syndromes such as hypomyelination with atrophy of the basal ganglia and cerebellum and leukoencephalopathy with brain-stem and spinal cord involvement and elevated white-matter lactate are described. Recent findings include evidence that mitochondrial fat-oxidation abnormalities may be important in the pathogenesis of adrenoleukodystrophy, and that a mutant myelin protein can cause maldistribution of other myelin proteins, causing dysmyelination, axonal damage, or both.

SUMMARY

This review focuses on advances in the understanding of the role of eIF2B as a cause of a common leukodystrophy syndrome. eIF2B-related disorders have a clinical spectrum ranging from a severe, rapidly progressive congenital or early infantile encephalopathy to a slowly progressive cognitive and motor deterioration often associated with premature ovarian failure. Two newly recognized leukodystrophy syndromes are described: hypomyelination with atrophy of the basal ganglia and cerebellum, and leukoencephalopathy with brain-stem and spinal cord involvement and elevated white-matter lactate. An update is also given for adrenoleukodystrophy and myelin-protein-related disorders. This update demonstrates that an increasing number of genetic defects are being identified that may cause primary white-matter disorders.