Groups of ethnically diverse swimmers also warrant the measurement of multiple vitamin D metabolites since differences exist in skin pigmentation (i.e., ultraviolet-B exposure) and genetic polymorphisms (i.e., vitamin D binding protein, vitamin D receptor phenotypes) that may be at greater risk of deficiency [43,44,45]. The gene discussed is VDR; the disease is hyperinsulinemic hypoglycemia, familial, 4.