Predominant antibody deficiencies: Bruton tyrosine kinase (BTK deficiency or X-linked agammaglobulinemia), Common variable immunodeficiency with no gene defect specified (CVID), activated p110 d syndrome (APDS), CD19 deficiency, NFKB1 deficiency, NFKB2 deficiency, and isolated immunoglobulin (Ig) G subclass deficiency with IgA deficiency. Here, BTK is linked to isolated agammaglobulinemia.