Vitamin d metabolism in familial benign hypercalcemia (hypocalciuric hypercalcemia) differs from that in primary hyperparathyroidism

We compared serum concentrations of immunoreactive PTH and plasma levels of vitamin Dmetabolites in 11 patients with adenomatous primary hyperparathyroidism and 32 individuals with the syndrome of familial benign hypercalcemia or familial hypocalciuric hypercalcemia (FHH). Serum immunoreactive PTH was elevated in the hyperparathyroid group but indistinguishable from control inFHH, despite comparable degrees of hypercalcemia. Plasma 25-hydroxyvitamin D concentrations were normal in both groups, but plasma 1,25-dihydroxyvitamin D levels in FHH were significantly lower than control (P < 0.0025) or hyperparathyroid (P < 0.01)values. FHH is pathogenetically distinct from primary hyperparathyroidism and should not be thought of simply as a variant of that condition.