Caytaxin is a neuron-restricted protein encoded by the gene Atcay/ATCAY. Mutations in the human ATCAY gene cause the rare neurological disorder Cayman ataxia [1], which is a congenital, non-progressive form of cerebellar ataxia characterized by marked motor defects and mental retardation [2]. The gene discussed is ATCAY; the disease is cerebellar ataxia.