Axonal Charcot–Marie–Tooth disease (CMT) is most frequently caused by mutations in the MFN2 gene (CMT2A) that can lead to various clinical phenotypes. The age at disease onset varies, but most cases occur before adolescence. We report two Japanese sisters who presented with middle-age-onset peripheral neuropathy with distinct clinical features. In the affected sisters, a homozygous missense mutation, c.1894C>T, p.R632W, corresponding to the transmembrane domain of MFN2 was identified; this mutation was heterozygous in another non-affected sibling, demonstrating co-segregation of the genotype and phenotype. The patients developed adult-onset slowly progressive muscle weakness that was predominant in the calf muscles and sensory disturbance. Magnetic resonance imaging revealed diffuse atrophy of the spinal cord, especially in the thoracic segment, and mild atrophy of the parietal lobe and the cerebellum in both patients. Electron microscopy of the sural nerve revealed clusters of round and swollen mitochondria. This is the first case report of adult-onset CMT2A with an autosomal-recessive inheritance pattern. The phenotype caused by the MFN2 mutation in these cases is very mild, considering that the mutation causes middle-aged-onset Charcot–Marie–Tooth even in the homozygous state. The mechanism of MFN2 mutation-induced toxicity is an interesting theme that awaits further investigations.
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Conficlt of interests
The authors declare that they have no competing financial interests.
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We thank the family for their participation in this study and Dr. Sachiko Kasai, Department of Neurology, Kyoto Kizugawa Hospital, who provided us the clinical information of a patient. This study was supported, in part, by grants from the research on the Nervous and Mental Disorders and Research Committee for Charcot–Marie–Tooth Disease, Neuropathy, Ataxic Disease and Applying Health and Technology of Ministry of Health, Welfare and Labour, Japan. This research is also supported by the research program for conquering intractable disease from Japan Agency for Medical Research and Development (AMED).