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 1HPT concentration (normal, less 0.2 ng/ml), urinary cAMP excretion per 100 ml glomerular filtrate (U cAMP/GF) (normal, 2.3 x/divided by 0.6 nmol/100 ml glomerular filtrate; mean, x/divided 1 SD), and renal tubular maximum of
phosphate transport corrected for glomerular filtration rate (
TMP/GFR; normal, 3.4 +/- 0.4 mg/dl; mean, +/- 1 SD). The group with 1HPT also diverged significantly from the group with FHH for all three indices: for PTH, 0.37 x/divided by .48 vs. 0.25 x/divided .46 (P less than 0.05); for UcAMP/GF, 4.3 x/divided by .53 vs. 2.6 x/divided .60 (P less than 0.0005); and for
TMP/GFR, 2.0 +/- 0.6 vs. 2.6 +/- 0.7 (P less than 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 UcAMP/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
calcium concentration, the group with FHH showed indices suggesting lower circulating PTH activity than the group with 1HPT.