ACTC1 and atrial fibrillation: We assessed the four independent AF SNPs on chromosome 4q25 for association with the expression of PITX2c, thus probing whether these SNPs serve as cis-eQTLs for PITX2c. None of these SNPs were associated with PITX2c levels when normalized to ACTC1, a cardiomyocyte-specific reference gene (p≥0.15, Table 6) or when normalized to PPIA, a reference gene expressed in all cell types (p≥25, Table 7).