GREM2 and Prolonged QT interval: The corresponding genes were then compared with Mendelian genes for arrhythmia disorders (atrial fibrillation, long-QT syndrome, short-QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome1,31,32) and with GWAS candidate variants associated with QT interval length and atrial fibrillation risk loci, described by Tucker et al2 and Arking et al.31 Of 45 Mendelian arrhythmia-associated genes (described in 3 reviews to 20151,31,32), 43 were annotated with ≥1 of the cardiac-relevant GO terms (Table II in the Data Supplement), with SRL and GREM2 being the exceptions.