Multiple dominant germ line mutations clustered in a single small domain of DNMT1 cause a heterogeneous group of adult-onset neurological disorders that include ataxia, sensorineural deafness, narcolepsy, dementia, psychosis, and other neurological and psychiatric abnormalities (OMIM 126375 and 605712) that are collectively known as autosomal dominant DNMT1 complex disorder [48]. The gene discussed is DNMT1; the disease is cerebellar ataxia.