[Siblings with spinocerebellar ataxia type 1 (SCA 1)--diagnosis by detecting the expansion of CAG repeat on chromosome 6p].

We reported siblings with spinocerebellar ataxia type 1 (SCA 1), diagnosed by detection of the expansion of CAG repeat in SCA 1 gene on chromosome 6. They were a 55-year-old woman (patient 1) and a 51-year-old woman (patient 2). There were eleven patients among the four generations in their family. They were from Obanazawa City in Yamagata Prefecture, located in the north-west region of Japan. The mode of inheritance was autosomal dominant. We confirmed the expansions of CAG repeat in SCA 1 gene in both patients. Clinically, they showed cerebellar ataxia and pyramidal signs especially in the lower extremities. The Patient 1 showed progressive external ophthalmoplegia without nystagmus, generalized amyotrophy and choreic movement of the fingers in advanced stage. On X-ray CT scan or MRI, the brainstem and cerebellum of the patient 1 were mildly atrophic, while those of the patient 2 showed normal appearances. Olivopontocerebellar atrophy is essential histopathological feature of SCA 1. However, some cases exhibit normal appearances of the brainstem on radiological imagings, because the brainstem involvement is often mild in SCA 1 patients.