BackgroundInfantile neuroaxonal dystrophy (INAD) is a rare autosomal-recessive neurodegenerative disorder. Patients with INAD usually show neurological symptoms with infant onset and die in childhood. Recently, it was reported that mutations in the PLA2G6 gene cause INAD, but neuropathological analysis of genetically confirmed individuals with neuroaxonal dystrophy has been limited.ResultsHere, we report a Japanese individual with neuroaxonal dystrophy associated with compound heterozygous mutations in the PLA2G6 gene. A novel splice-site mutation resulting in skipping and missense mutations (p.R538C) in exon 9 was identified in the patient. This patient initially presented with cerebellar ataxia at the age of 3 years, which was followed by symptoms of mental retardation, extrapyramidal signs, and epileptic seizure. The patient survived until 20 years of age. Neuropathological findings were characterized by numerous axonal spheroids, brain iron deposition, cerebellar neuronal loss, phosphorylated alpha-synuclein-positive Lewy bodies (LBs), and phosphorylated-tau-positive neurofibrillary tangles. In particular, LB pathology exhibited a unique distribution with extremely severe cortical involvement.ConclusionsOur results support a genetic clinical view that compound heterozygous mutations with potential residual protein function are associated with a relatively mild phenotype. Moreover, the severe LB pathology suggests that dysfunction of the PLA2G6 gene primarily contributes to LB formation.
Genetic and phenotypic heterogeneities are considerably high in adult-onset leukoencephalopathy, in which comprehensive mutational analyses of the candidate genes by conventional methods are too laborious. We applied exome sequencing to conduct a comprehensive mutational analysis of genes for autosomal dominant leukoencephalopathies. Genomic DNA samples from four patients of three families with autosomal dominantly inherited adult-onset leukodystrophy were subjected to exome sequencing. On the basis of the results, 21 patients with adult-onset sporadic leukodystrophy and one patient with pathologically proven HDLS were additionally screened for CSF1R mutations. Exome sequencing identified heterozygous CSF1R mutations (p.I794T and p.R777W) in two families. I794T has recently been reported as a causative mutation for hereditary diffuse leukoencephalopathy with spheroids (HDLS), and R777W is a novel mutation. Although mutational analysis of CSF1R in 21 sporadic cases revealed no mutations, another novel CSF1R mutation, p.C653Y, was identified in one patient with autopsy-proven HDSL. These variants were located in the PTK domain where the causative mutations cluster. Functional prediction of the mutant CSF1R as well as cross-species conservation of the affected amino acids supports the notion that these variants are pathogenic for HDLS. Exome sequencing is useful for a comprehensive mutational analysis of causative genes for hereditary leukoencephalopathies, and CSF1R should be considered a candidate gene for patients with autosomal dominant leukoencephalopathies.
Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is a familial neurodegenerative disease clinically characterized by progressive cognitive and motor dysfunction. Mutations in the colony-stimulating factor 1 receptor (CSF1R) gene have recently been identified in HDLS patients. The presence of diffuse axonal spheroids, myelin loss, and pigmented microglia in the white matter are pathologic hallmarks of HDLS; however, early pathologic findings have not been described in HDLS patients. We report a Japanese family with HDLS. A novel heterozygous c.653 C>Y mutation in the CSF1R gene was identified in the female proband who died at the age of 63 years; postmortem findings were compatible with HDLS. We also autopsied her sister who was considered to be neurologically asymptomatic and died of tuberculosis at the age of 44 years. Postmortem studies revealed patchy axonal degeneration and myelin loss, predominantly in the subcortical white matter. Pigmented microglia were distributed diffusely throughout the cerebral white matter and expressed CSF1R poorly. In conclusion, our observations suggest that the pathology of HDLS may initially be characterized by multifocal lesions in subcortical white matter regions. Moreover, pigmented microglia poorly express CSF1R and are distributed diffusely throughout the white matter at the early disease stage, preceding axonal damage and myelin loss.
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