Specific criteria of CM, defined by the EU/US consensus group, include the absence of signs or criteria of SM, and the presence of typical skin lesions of mastocytosis associated with the Darier’s sign, which is a major CM criterion, and one or two of the following minor criteria: increased numbers of MCs in biopsy sections of lesional skin and an activating KIT mutation in lesional skin [5,84]. This evidence concerns the gene KIT and mastocytosis.