HCN4 and atrial fibrillation: GWAS meta-analyses have provided additional risk variants associated with AF, implicating six new loci in AF; CAV1, HCN4, SYNE2, SYNPO2L, PRRX1 and WNT8A [140,142,143], but importantly, the most relevant associated risk variants are those located in the vicinity of the PITX2 locus [104,105,106,107,144,145,146,147].