Hemizygous loss-of-function variants in the MAGT1 gene lead to a rare primary immunodeficiency known as X-linked MAGT1 deficiency with increased susceptibility to Epstein-Barr virus (EBV) infection and N-linked glycosylation defect (XMEN, previously known as X-linked immunodeficiency with magnesium defect, EBV infection, and neoplasia) disease (Ravell et al., 2020a). Here, MAGT1 is linked to hyperinsulinemic hypoglycemia, familial, 4.