Contributor: Gordon K. Klintworth
Spinocerebellar ataxia type I (olivopontocerebellar atrophy type I, spinocerebellar degeneration type I, spinocerebellar atrophy I, Menzel type spinocerebellar atrophy, OMIM #164400) is one of several types of olivopontocerebellar atrophy, spinocerebellar ataxia  and spinocerebellar degeneration . It is an autosomal dominant inherited degenerative disorder of the central nervous system that involves neurons in the cerebellum, olives in the brain stem and tracts in the spinal cord. The condition results from CAG trinucleotide repeats within the ATX1 gene that encodes for ataxin-1. Normal individuals contain 19-36 of the CAG repeats within the gene; affected persons have 40-81 CAG repeats. The disease is manifest by ataxia, an intention tremor, rigidity, loss of deep tendon reflexes, and a loss of vibration and pain sensation. The manifestations include nystagmus. Alpha synuclein is present in neuroglia and neurons of affected persons.