Some of these rare primary immunodeficiencies caused by STAT3 mutations [31, 84] are characterized by extremely high serum IgE levels (often above 10,000 kU/L) and are associated with a pruritic eczematous skin rash, eosinophilia and impairments of other organ systems including intelligence and motor function. Here, IGHE is linked to Increased total eosinophil count.