While it seems now well established that decreased venous P50 is strongly suggestive of HOAH (or rarely of bisphosphoglycerate mutase deficiency), which is then confirmed by sequencing of globin or BPGM genes, it seems difficult to make a statement about its predictive value when within the normal range. The gene discussed is BPGM; the disease is hyperinsulinemic hypoglycemia, familial, 4.