According to the EU/US consensus group, the diagnostic criteria of CM include the presence of typical skin lesions of mastocytosis together with the Darier’s sign, which is a major CM criterion, and one or two of the minor criteria—increased numbers of MCs in biopsy sections of lesional skin and an activating KIT mutation at codon 816 in lesional skin [6,9]. The gene discussed is KIT; the disease is mastocytosis.