While nearly all subspecialist immunologists who treat patients with PID commonly recommend IVIG therapy for their patients with Bruton’s agammaglobulinemia (X-linked agammaglobulinemia; XLA), CVID, hyper IgM syndrome (hyper IgM), and severe combined immunodeficiency disease (SCID), significantly fewer family practice physicians recommended IVIG therapy for these same diagnoses: XLA, 100 vs. 71% (P < 0.05); CVID, 98 vs. 42% (P < 0.05); hyper IgM, 92 vs. 23% (P < 0.05), and SCID, 92 vs. 75% (P < 0.05) (Figure 3). The gene discussed is CD40LG; the disease is isolated agammaglobulinemia.