Machado-Joseph disease (MJD)—also called spinocerebellar ataxia Type 3 (SCA3)—is one of approximately 30 recognized, dominantly inherited forms of ataxia.
Ataxia is a general term meaning lack of muscle control or coordination.
The name “Machado-Joseph” comes from two families of Portuguese/Azorean descent who were among the first families described with the unique symptoms of the disease in the 1970s. The prevalence of the disease is highest among people of Portuguese/Azorean descent. For example, among immigrants of Portuguese ancestry in New England, the prevalence is around one in 4,000, and the highest prevalence in the world, about one in 140, occurs on the small Azorean island of Flores. Soon after the gene defect was discovered, a hereditary ataxia in European families known as SCA3 was found to be caused by the exact same mutation. Thus, SCA3 and MJD are the same disorder.