Unrestrained IL-7R signaling promotes B cell precursor proliferation leading to increased B cell production in humans (Parrish et al., 2009), and gain-of-function IL-7R mutations increase peripheral B cell numbers and contribute to precursor B cell ALL (Almeida et al., 2021; Shochat et al., 2011). The gene discussed is IL7R; the disease is acute lymphoblastic leukemia.