a group of genetically distinct, mostly autosomal dominant progressive neurologic diseases characterized by loss of neurons in the cerebellar cortex, basis pontis, and inferior olivary nuclei; results in ataxia, tremor, involuntary movement, and dysarthria; five clinical types (four with dominant in heritance, one with recessive) have been described, each characterized by additional findings, such as sensory loss, retinal degeneration, ophthalmoplegia, and extrapyramidal signs. Several loci are involved, autosomal dominant [MIM*164400-*164600] and recessive [MIM*258300].spinocerebellar ataxia. SYN: olivopontocerebellar degeneration.