Mycobacterial diseases are reported in patients with inborn errors of the canonical NF-κB pathway affecting the IL-12/IFN-γ circuit, including X-linked (XL) NEMO, AR IKK-β, and AR c-Rel deficiencies [37, 38, 45], and opportunistic intestinal parasitic infections (cryptosporidiosis and microsporidiosis) are seen in patients with inborn errors of IL-21 signaling (AR IL-21R deficiency) or the CD40-dependent dendritic cell–T cell synapse (AR CD40, XL-CD40L, AR MHC class II deficiency, AR c-Rel deficiency, and AR FLT3L deficiency) (38, 46, 47, 48). The gene discussed is REL; the disease is microsporidiosis.