HCN4 and atrial fibrillation: As far as the K+ channel genes are concerned, the genes whose mutations increase the risk of AF occurrence are ABCC9 (I KATP), HCN4 (I f), KCNA5 (I Kur), KCND3 (I Ks), KCNE1 (IKs), KCNE2 (IKs), KCNE3 (IKs), KCNE4 (IKs), KCNE5 (IKs), KCNH2 (IKr), KCNJ2 (I K1), KCNJ5 (I KAch), KCNJ8 (I KATP), KCNN3 (IAHP), and KCNQ1 (IKs) [92].