These heterozygous repeat expansions lead to dominantly inherited cerebellar ataxias, involving seven genes: ATXN1 (MIM: 601556) involved in SCA1 (MIM: 164400), ATXN2 (MIM: 601517) involved in SCA2 (MIM: 183090) and certain forms of Parkinsonism, ATXN3 (MIM: 607047) involved in SCA3 (MIM: 109150), CACNA1A (MIM: 601011) involved in SCA6 (MIM: 183086) and episodic ataxias, ATXN7 (MIM: 607640) involved in SCA7 (MIM: 164500), TBP (MIM: 600075) involved in SCA17 (MIM: 607136).1 The gene discussed is CACNA1A; the disease is Familial paroxysmal ataxia.