There was one pair of identical infant twins with concordant ALL and KMT2a-R (#2.4), one pair of identical twins with AML RUNX1-RUNX1T1 (#3.3), one identical twin set in which only one member was affected with ALL (#2.3), and one non-identical twin set with discordant leukemia subtypes, AML-M3 and c-ALL (#3.2). The gene discussed is RUNX1T1; the disease is acute myeloid leukemia.