CACNA1A and episodic ataxia type 2: Episodic ataxia type 2 (EA2, MIM #108500) is a rare autosomal dominant ion channel disorder caused by mutations in the CACNA1A gene and characterized by episodes of midline cerebellar disturbance manifesting as ataxia, imbalance, vomiting, oscillopsia1 and interictal nystagmus; progressive ataxia can eventually develop2.