Studies have linked cardiac arrhythmogenesis to mutations in the genes encoding the cardiac sodium channel (NaV1.5) and AF-causing variants have been reported in both the α-subunit (encoded by the SCN5A gene) and associated β-subunits (Navβ) (encoded by the genes SCN1B–SCN4B) [13,14,15,16,17]. Here, SCN4B is linked to atrial fibrillation.