In this group of patients, mutations in IDH2 (n = 3), KRAS (n =3), KIT (n = 3), and SETD2 (n = 1) were identified at low AF (median, 0.86%; range, 0.68 to 2.9%), though the corresponding mutation in the primary tumor was not known. The gene discussed is SETD2; the disease is atrial fibrillation.