Subjects with IL-6R deficiency present with recurrent skin and lung infections, eczema, high IgE levels, and eosinophilia [30], whereas patients with IL-21R deficiency suffer from recurrent respiratory tract infections and exhibit impaired B cell proliferation, immunoglobulin class-switch and reduced T cell effector function [31]. Here, IL21R is linked to hyperinsulinemic hypoglycemia, familial, 4.