Machado-Joseph disease was first described in 1972 among the descendants of Portuguese-Azorean immigrants to the United States, including the family of William Machado

Machado-Joseph disease presents a 94.5% penetrance, which means that 94.5% of the mutation carriers will develop the symptoms during their lives, and less than 5% will remain free of symptoms

Ultimately, MJD leads to paralysis or a crippling condition, although intellectual functions usually remain normal. Other names of MJD are Portuguese-Azorean disease, Joseph disease, Azorean disease

The disease involves the slow and progressive degeneration of brain areas involved in motor coordination, such as the cerebellar, extrapyramidal, pyramidal, and motor areas

As MJD progresses slowly, most patients survive until middle age or older.