It was demonstrated that Il7r mutants are capable of blocking thymocyte differentiation at the DN2 stage and inducing ETP-ALL in transplanted mice [11]; moreover, the concomitant introduction of Runx1 and Jak3 mutations in hematopoietic stem and progenitor cells in mice gave rise to T-ALL with the ETP phenotype [12]. The gene discussed is JAK3; the disease is acute lymphoblastic leukemia.