IGHM and agammaglobulinemia: While the majority of patients with agammaglobulinemia are male, suggesting X-linked inheritance and mutations in BTK, there are a handful of genes that, if mutated, result in autosomal recessive agammaglobulinemia, including IGHM (μ heavy chain deficiency), IGLL1 (λ5 deficiency), CD79A (Igα deficiency), CD79B (Igβ deficiency), BLNK, PIK3R1 (1), IKAROS (16), and one gene (TCF3, E47 deficiency) causing an autosomal-dominant agammaglobulinemia (17).