Several patients had extremely rare immunodeficiencies, such as severe combined immunodeficiency secondary to MALT1, ITK, or IL2RG (X-linked) deficiencies, as well as Nijmegen breakage syndrome, interferon gamma receptor defects, adenosine deaminase 2 deficiency, and X-linked lymphoproliferative disorder. Here, ADA2 is linked to hyperinsulinemic hypoglycemia, familial, 4.