Mice and at least one patient genetically deficient for DBP have been shown to have profoundly decreased plasma concentrations of 25OHD which were not corrected by vitamin D supplementation, however this patient and mice showed no clinical signs of Vitamin D deficiency, suggesting that DBP deficiency increased bioavailable 25OHD concentrations enough to support calcium homeostasis despite very low total 25OHD concentrations [8–10]. This evidence concerns the gene DBP and hyperinsulinemic hypoglycemia, familial, 4.