An autosomal dominant inherited disorder, usually beginning in middle age, featuring insidious progression of mental abnormalities associated with frontal lobe dysfunction (emotional, personality, and intellectual) and motor abnormalities associated with basal ganglion damage (formerly called Huntington's chorea). Although there are exceptions, most patients with this disorder deteriorate to a vegetative state in 10-15 years. Pathological examination of the brain reveals extensive degeneration of the striatum, and to a lesser extent, frontal cortex. Molecular biology reveals abnormal expansion of the triplet repeat at the 3' end for the coding region of a newly characterized gene; its function is not yet understood.