Abnormal trinucleotide repeat expansion in the CACNA1A gene causes spinocerebellar ataxia type 6 (SCA6, OMIM #183086), which normally presents in adulthood with progressive gait ataxia, incoordination, tremors, dysarthria, and nystagmus (Case y & Gomez, 1998). The gene discussed is CACNA1A; the disease is pathologic nystagmus.