Siblings with cystic leukoencephalopathy and megalencephaly

Molecular genetic studies in Indian patients with megalencephalic leukoencephalopathy

Mutations in the MLC1 gene cause megalencephalic leukoencephalopathy with subcortical cysts. We sought to identify mutations in the MLC1 gene, to evaluate the genotype-phenotype correlation, and to develop a strategy for diagnosing Indian patients with megalencephalic leukoencephalopathy. Forty patients were enrolled. We developed a rapid restriction fragment length polymorphism method to screen a common mutation, c.135_136insC. Rare and novel mutations were screened by conformation-sensitive gel electrophoresis, followed by sequencing. Three previously reported and two novel mutations were identified in 37 patients. The presence of the c.135_136insC mutation in 29 patients of the Agarwal community suggests a founder effect. The mutation c.959C>A was evident in four patients, and appears to be the second commonest mutation. Genotype could not predict phenotype. We recommend screening for the commonest mutation (c.135_136insC), followed by the next commonest mutation (c.959C>A), and then other rare mutations, using conformation-sensitive gel electrophoresis analysis or direct sequencing.

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.

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.

A common mutation and a novel mutation in Japanese patients with van der Knaap disease

Van der Knaap disease, or megalencephalic leukoencephalopathy with subcortical cysts (MLC), is an autosomal recessive disorder clinically characterized by macrocephaly, ataxia, spasticity, and mental decline. Magnetic resonance imaging (MRI) shows swollen brain with diffuse white-matter abnormalities and subcortical cysts, particularly in the anterior-temporal region. Recently, the MLC1 gene was identified as the gene responsible for this disorder, and mutations in this gene were described in several patients. We studied three Japanese patients with van der Knaap disease at the molecular genetic level. Two of them were homozygous for a previously-described mutation, S93L, and one was a compound heterozygote for S93L and a novel mutation, 452-468del+g, which leads to frameshift with a premature termination codon. Combining our data with previous reports allowed us to estimate the molecular genetic basis of this disorder in seven Japanese patients. In summary, S93L was observed in six of seven (85.7%) patients at least in one allele, and ten of 14 (71.4%) alleles had this mutation. Therefore, S93L appears to be fairly frequent in Japanese patients with van der Knaap disease, and analysis for this mutation in DNA isolated from leukocytes would provide for an easy and precise diagnosis of this disorder in Japanese patients.

Epilepsy in vacuolating megalencephalic leukoencephalopathy with subcortical cysts

Vacuolating megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a disorder characterised by acquired macrocephaly, developmental motor delay of varying degrees, slowly progressive cerebellar and pyramidal signs, and initially preserved intellectual function. More than 60% of the published cases had epileptic seizures. In this study, we analysed the seizures and EEG findings of nine patients with MLC. Six patients (66.6%) with moderate to severe neurological impairment had epilepsy, four with partial and two with generalised seizures. The EEG of five epileptic patients revealed epileptogenic foci over the temporal, frontal and parietal regions with variable predominance during waking and sleep. The facilitation of spike-and-wave paroxysms by eye closure, by intermittent photic stimulation and by hyperventilation were determined in four patients. Four patients also showed abnormalities in the background activity. In conclusion, we think that epilepsy is a significant component of MLC compared to the other leukodystrophies. The elucidation of the underlying molecular defect may explain the unusual pathogenetic relation between this leukoencephalopathy and the associated seizures.