Initial descriptions of patients with NFKB1 gene mutations were associated with an immunodeficiency phenotype consisting of recurrent respiratory tract infections leading to chronic lung disease with bronchiectasis, diarrhea, lymphadenopathy, splenomegaly, recurrent autoimmune phenomena (hemolytic anemia, thrombocytopenia, and leukopenia), hypogammaglobulinemia, deficient production of specific antibodies, and decreased class-switched and memory B cells (175, 176). Here, NFKB1 is linked to agammaglobulinemia.