CACNA1A and episodic ataxia type 2: By contrast, FHM1 and some rare forms of EA2 are usually associated with gain-of-function mutations, resulting in enhanced open probability or conductance of CaV2.1 [40, 44–46], whereas SCA6 is associated with abnormal CAG-repeat expansion within a C-terminal exon of CACNA1A, which may induce cytotoxicity of the resulting protein or dysregulated gene expression due to altered function of the α1 ACT protein [43, 47, 48].