KCND3 and spinocerebellar ataxia type 19/22: We analyzed the clinical and molecular features of three KCND3 variants, associated with SCA19/22 or congenital ataxia, underscoring the pathogenic role of impaired protein expression and reduced K+ currents with variable effects on channel gating in the dominant negative effect of different types of ataxia causing KV4.3 mutants.