There are several other examples of reversions underlying incompletely penetrant clinical disease, for ADA (162, 185), XLA (186, 187), WASP (188, 189), leukocyte adhesion deficiency (190), X-linked immunodeficiency with ectodermal dysplasia due to variants in NEMO (191), Omenn syndrome with CARD11 deficiency (192), IKBKG-associated immunodeficiency (16), and GATA2 deficiency (193). Here, BTK is linked to hyperinsulinemic hypoglycemia, familial, 4.