Circulating Parathyroid Hormone Activity: Familial Hypocalciuric Hypercalcemia Versus Typical Primary Hyperparathyroidism*

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Abstract
Three indices of circulating parathyroid hormone (PTH) activity were compared between two groups: the first a group of 23 patients from three large kindreds with autosomal dominant hypercalcemia without hypercalciuria [familial hypocalciuric hypercalcemia (FHH)] and the second a group of 64 patients with typical primary hyperparathyroidism (1HPT) manifesting comparable hypercalcemia. The group with 1HPT differed from normal with respect to plasma PTH concentration (normal, vs. 0.25 ×/÷.46 (P < 0.05); for Ucamp/GF, 4.3 ×/÷.53 vs. 2.6 ×/÷60 (P < 0.0005); and for TMP/GFR, 2.0 ± 0.6 vs. 2.6 ± 0.7 (P < 0.01). The between-group differences for all three indices were also significant after adjustment for their variation with serum calcium. However, only the difference in TmP/GFR remained significant after adjustment for covariance attributable to serum calcium concentration, age, and creatinine clearance. The group with FHH differed from normal for TmP/GFR but not for Ucamh/GF. However, analysis of changes in Ucamp/GF and serum calcium concentration around the time of parathyroidectomy in three patients with FHH suggested that the parathyroid glands contributed to the abnormalities of mineral homeostasis in at least one. It was concluded that higher serum concentrations of PTH do not account for the lower renal clearance of calcium and magnesium in FHH vs. that in 1HPT, because at any elevation of serum calcium concentration, the group with FHH showed indices suggesting lower circulating PTH activity than the group with 1HPT.