Somatic chimerism has been observed in several primary immunodeficiencies such as Wiskott Aldrich Syndrome [24–27], ADA-deficiency [28, 29] or X-linked SCID [30, 31] and is possibly associated with an amelioration of the clinical phenotype of disease [32]. Here, ADA is linked to hyperinsulinemic hypoglycemia, familial, 4.