IKBKG and Down syndrome: CVID, common variable immunodeficiency; hyper-IgM, hyper immunoglobulin M syndrome; IKBKG, inhibitor of nuclear factor kappa B kinase subunit gamma; IPD, invasive pneumococcal disease; IRAK, interleukin-1 receptor-associated kinase; MBL, mannose-binding lectin; MYD88, myeloid differentiation primary response 88; NEMO, NF-κB essential modulator; NFKB1, nuclear factor kappa B subunit 1; SPAD, specific polysaccharide antibody deficiency; TLR, Toll-like receptor; XLA, X-linked agammaglobulinemia