SH2D1A and hyperinsulinemic hypoglycemia, familial, 4: The single case of IL-21 deficiency presented with recurrent sinopulmonary infections and early onset colitis (Salzer et al., 2014), while ∼50% of patients with XL lymphoproliferative disease due to SH2D1A mutations (encoding SAP) have recurrent infections and impaired vaccine responses (Ma et al., 2007).