Dysbiosis of the intestinal microbiome has been observed in some inborn errors of immunities (IEIs)/primary immunodeficiency disease, such as chronic granulomatous disease (CGD) (Sokol et al., 2016), X-linked inhibitor of apoptosis (XIAP) deficiency (Sokol et al., 2016; Ono et al., 2021), tetratricopeptide repeat domain 7A (TTC7A) deficiency (Sokol et al., 2016), common variable immunodeficiency (CVID) (Jørgensen et al., 2016; Varricchi et al., 2021), and Wiskott–Aldrich syndrome (Zhang et al., 2020). The gene discussed is XIAP; the disease is hyperinsulinemic hypoglycemia, familial, 4.