FGF14 and spinocerebellar ataxia type 27: Inherited loss-of-function mutations in the FGF14 coding region disrupt the trafficking of Nav α subunits to the AIS, attenuate Nav current densities, and impair excitability of hippocampal neurons [128,130]—phenotypes that are thought to contribute to spinocerebellar ataxia 27 (SCA27) [129,131].