Conversely, the dysregulation of MCs is central to the pathogenesis of numerous diseases, including allergic diseases driven by IgE-mediated activation, as well as a spectrum of Mast Cell Activation Disorders (MCADs), such as Mastocytosis, Mast Cell Activation Syndrome (MCAS), and Hereditary Alpha-Tryptasemia (HAT), all characterized by inappropriate mediator release. Here, IGHE is linked to mastocytosis.