FHH is distinguished from primary hyperparathyroidism by the Early age of onset Absence of symptoms Frequent occurrence of hypermagnesemia Presence of hypercalcemia without hypercalciuria in other family members Low fractional excretion of calcium, which is the ratio of calcium clearance to creatinine clearance (< 1% in FHH; 1 to 4% in primary hyperparathyroidism) Elevated or normal intact PTH Altered feedback regulation of the parathyroid glands may be responsible for the elevated or normal intact PTH level.