Recent research has validated that TBX5 transcriptionallyregulates expression of many target genes, including NPPA,GJA5, MYH6 and SCN5A,separately or together with GATA4, GATA6, NKX2-5, MEF2C and TBX20 (Steimle and Moskowitz1, 2017), and variationsin TBX5 and its target genes as well as cooperative partners have been reported toresult in CHD and/or AF in humans (Postma etal., 2008; Mahida,2014; Guo et al.,2016; Ma et al.,2016; Wang et al.,2016; Li and Yang, 2017; Campbell and Wehrens, 2018). The gene discussed is MEF2C; the disease is atrial fibrillation.