TPH1 and hyperinsulinemic hypoglycemia, familial, 4: Instead of exploring a linear relationship between TPH and 25(OH)D value, as already proposed by other authors with inconclusive results, we classified patients in three standard groups according to their 25(OH)D level, defined as deficiency (< 10 ng/ml), insufficiency (11–30 ng/ml) and normality (> 30 ng/ml) [9–12, 18].