The First Case of Spinocerebellar Ataxia Type 8 in Monozygotic Twins.

Spinocerebellar ataxia type 8 (SCA8) is a rare hereditary cerebellar ataxia showing mainly pure cerebellar ataxia. We herein report cases of SCA8 in Japanese monozygotic twins that presented with nystagmus, dysarthria, and limb and truncal ataxia. Their ATXN8OS CTA/CTG repeats were 25/97. They showed similar manifestations, clinical courses, and cerebellar atrophy on magnetic resonance imaging. Some of their pedigrees had nystagmus but not ataxia. These are the first monozygotic twins with SCA8 to be reported anywhere in the world. Although not all subjects with the ATXN8OS CTG expansion develop cerebellar ataxia, these cases suggest the pathogenesis of ATXN8OS repeat expansions in hereditary cerebellar ataxia.