IKBKB and agammaglobulinemia: Rare mutations in IKBKB have been reported, which lead to absence of protein expression and confer severe early onset immunodeficiency with hypogammaglobulinemia or agammaglobulinemia, low memory B cell numbers, impaired lymphocyte proliferation, NF-κB signaling, lymphocyte differentiation and activation, and deficiency of Treg cells and γδ T cells (11–13).