PITX2 and atrial fibrillation: AF risk is linked to common single nucleotide polymorphisms (SNPs) at dozens of loci (7, 8), including the noncoding AF-associated region (AFAR) at the 4q25 locus in enhancers controlling PITX2 expression (9), which encodes the developmentally critical, paired-like homeodomain transcription factor (TF), PITX2.