CACNA1G and Nystagmus: SCA42 is an autosomal dominant neurologic channelopathy disorder characterized predominantly by gait instability, tremor (i.e. intention, postural, head, and resting) and additional cerebellar signs (i.e. dysarthria, nystagmus and saccadic pursuits), and is caused by a heterozygous mutation in CACNA1G. There is variable age at onset (range 9- >78 years) and slow progression of the disease.