The incidence of protein S deficiency in Western studies ranges from 0.8 to 3.2%14,15 and, when combined with protein C and antithrombin, these account for 5-10% of the cases.15 It is quite possible that our higher results were due to the testing method and also that some of these were not due to inherited deficiency, since family studies were not performed. This evidence concerns the gene PROS1 and hyperinsulinemic hypoglycemia, familial, 4.