KIT and systemic mastocytosis: Of note, all 6 responding patients reported previously, as well as the three K509I+ patients who achieved CR in our series, were diagnosed with WDSM or had features highly suggestive of such variant of SM (e.g. childhood onset, female gender, familial aggregation and mature-appearing, round shape CD25− BM MCs), supporting the close association of mutations involving the extracellular membrane and transmembrane domains of the KIT gene with WDSM [19].