Regarding the skin, despite the forms of urticaria triggered by IgE or non-IgE mediated mechanisms, MCs can be involved in cutaneous manifestations in the course of mastocytosis, with maculopapular cutaneous mastocytosis—previously known as urticaria pigmentosa—isolated or multifocal cutaneous mastocytomas, and diffuse cutaneous mastocytosis [53]. The gene discussed is IGHE; the disease is mastocytosis.