KCND3 and attention deficit-hyperactivity disorder: Only a few cases carrying de novo KCND3 variants with developmental delay and congenital ataxia have been reported including a patient with early onset cerebellar ataxia complicated by intellectual disability, epilepsy, attention deficit hyperactivity disorder, strabismus, oral apraxia and joint hyperlaxity carrying a de novo p.R293_Phe295 duplication in the voltage-sensor domain (Figure S4) of the KV4.3 channel causing a severe shift in channel gating to more depolarized voltages [4].