INPP5A and spinocerebellar ataxia type 17: In combination with the protective effect of INPP5A against Purkinje cell degeneration, we propose that INPP5A plays a critical role in selective neurodegeneration in SCA17 because mutant TBP impairs its expression to affect IP3/Ca2+ signal pathway, leading to Purkinje cell degeneration (Fig. 6i).