ASXL1 regulates the delicate interplay between proliferation and differentiation of stem progenitor cell populations (9, 35) and therefore, both germline and somatic ASXL1 mutations disrupt the proliferation-differentiation balance and promote stem-cell identity over differentiation in BOS and myeloid leukemias. The gene discussed is ASXL1; the disease is Buschke-Ollendorff syndrome.