De novo expansion of a CAG repeat in a Japanese patient with sporadic Huntington's disease.

A 49-year-old man was admitted to our hospital complaining of dysarthria and involuntary movements of his neck and extremities. He had first begun to experience involuntary neck movements at the age of 40 and his symptoms gradually progressed thereafter. There was no family history of neurological disorders. On admission he showed memory disturbance, dysarthria, and choreic movements. The involuntary movements affected his face, neck, trunk, and extremities. MRI of the brain revealed atrophy of both the cerebral cortex and the head of the caudate nucleus. DNA samples for molecular analysis were obtained from the patient and both of his parents. In this pedigree, the father carried a premutated allele of 35 CAG repeats and transmitted an expanded allele of 43 CAG repeats to his son. Paternity and maternity were analyzed using a microsatellite marker located in a different chromosome. To our knowledge, this is the first report of a sporadic case of Huntington's disease in a non-caucasian population in which the disease prevalence is much lower than that in the caucasian population. A new mutation in the current Japanese population which shares the same mechanism as de novo mutation in Caucasians may have contributed to the frequency of HD in Japan at the present time.