The high association of JAK1/2 mutations with CRLF2r (Mullighan et al., 2009a; Mullighan et al., 2009c; Russell et al., 2009; Pui et al., 2017; Reshmi et al., 2017) in ALL suggests that these events functionally cooperate to drive lymphoid transformation (Russell et al., 2009; Tasian and Loh, 2011; Kim et al., 2018). The gene discussed is JAK1; the disease is acute lymphoblastic leukemia.