[Overview of Hereditary Spinocerebellar Ataxias in Japan].

Hereditary spinocerebellar degenerations (SCD) are a group of neurodegenerative disorders characterized by slowly progressive ataxia associated with non-cerebellar neurological signs and symptoms. In the Japanese population, dominantly inherited SCDs are much more common than recessively inherited or X-linked SCDs. The most common dominantly inherited SCD in Japan, as well as in many other countries, is Machado-Joseph disease, also known as spinocerebellar ataxia type 3 (MJD/SCA3). MJD/SCA3 is frequently accompanied by non-cerebellar symptoms, including progressive external ophthalmoplegia, pyramidal signs, dystonia, rigidity, dysarthria, and distal muscle atrophies. SCA6 and SCA31 represent a pure cerebellar subtype of SCD, occasionally accompanied by non-cerebellar signs. Detailed medical history and neurological examination are important for clinicians to diagnose hereditary SCDs, although genetic testing can help confirm the diagnosis. Despite increasing understanding of the molecular mechanisms underlying these fatal diseases, preventive therapies are currently lacking.