The familial aggregation of leukemia in siblings with somatic aberrations such as ETV6-RUNX1, KMT2-A-r, and NOTCH1 mutations that we have previously reported (as case reports in siblings) in international collaboration and age at the time of leukemia diagnosis were significantly correlated with somatic mutations that initiate during fetal life (high hyperdiploidy, ETV6-RUNX1, KMT2A-r, TCR-rearrangements, and NOTCH1 mutation) (17, 27–30). This evidence concerns the gene RUNX1 and leukemia.