Our results demonstrate that the incidence of clonal hemopoiesis is much higher than suggested by exome-sequencing studies, that spliceosome gene mutations drive clonal outgrowth primarily in the context of an aging hemopoietic compartment, and that NPM1 mutations do not drive ARCH, indicating that their acquisition is closely associated with frank leukemia. The gene discussed is TSLIG1; the disease is leukemia.