Idiopathic Hypercalciuria and Hereditary Hypophosphatemic Rickets

Abstract

Among 59 closely related members of one Bedouin tribe, we identified 9 who had the characteristic features of hereditary hypophosphatemic rickets with hypercalciuria (HHRH). We found "idiopathic" hypercalciuria in 21 of the 50 asymptomatic members. The biochemical abnormalities observed in these 21 subjects were qualitatively similar to those in the 9 with HHRH, but were quantitatively milder. The urinary calcium concentration was 0.43±0.14 mg per milligram of creatinine (mean ±SD) in the patients with HHRH, 0.34±0.07 in the subjects with idiopathic hypercalciuria, and 0.14±0.05 in normal subjects from the same tribe. Tubular reabsorption of phosphorus and serum phosphorus concentrations were 3.0 and 4.3 SD units below the age-related mean, respectively, in HHRH, and 1.1 SD units below the normal mean for both variables in idiopathic hypercalciuria. Mean serum levels of 1,25-dihydroxyvitamin D (1,25-(OH)₂D) were 303 pg per milliliter in HHRH and 145 pg per milliliter in idiopathic hypercalciuria (upper normal limit, 110).