NAV1 and cardiac conduction defect: As mutations in fhf1 are associated with epileptic encephalopathy (For CENetDDD Study group‡* et al., 2016) and cardiac conduction disorders (Hennessey et al., 2013) while mutations in fhf4 are linked to spinocerebellar ataxia (Brusse et al., 2006), resolving the dynamic interplay between CaM and fhf in tuning NaV1 may be critical for understanding pathogenic mechanisms.