European Journal of Endocrinology (2001) 144 263±269 ISSN 0804-4643 CLINICAL STUDY Skeletal responsiveness to parathyroid hormone in pseudohypoparathyroidism Masanori Kanatani, Toshitsugu Sugimoto, Hiroshi Kaji, Kazuto Ikeda and Kazuo Chihara Third Division, Department of Medicine, Kobe University School of Medicine, Kobe 650, Japan (Correspondence should be addressed to T Sugimoto, Third Division, Department of Medicine, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650, Japan; Fax: 181-78-3825899) Abstract Background: Although there have been some case reports suggesting that bone in patients with pseudohypoparathyroidism (PHP) might respond to parathyroid hormone (PTH), no information is available as to whether serum PTH concentration is related to bone metabolic markers or to bone mineral density (BMD) in PHP. Objective: To address these relationships, by comparing intact serum PTH, bone metabolic markers and BMD in patients with PHP with those in patients with idiopathic hypoparathyroidism (IHP) and postoperative hypoparathyroidism (OHP). Methods: Intact serum PTH, bone metabolic markers (osteocalcin, tartrate-resistant acid phosphatase, pyridinoline, deoxypyridinoline) and BMD by dual-energy X-ray absorptiometry or single-photon absorptiometry were measured in patients with PHP Ia n 2 and PHP Ib n 8 : The results were compared with those in patients with IHP n 5 and OHP n 14 : Results: All bone metabolic markers measured were present in significantly greater amounts in patients with PHP Ib than in those with IHP+OHP. The Z score (standard deviation of average BMD at each age) of the BMD of femoral neck was significantly lower in patients with PHP Ib than in those with IHP+OHP. The Z scores of BMD of lumbar spine and radius were also lower in patients with PHP Ib than in those with IHP+OHP, but the difference was not significant. Moreover, the intact serum PTH concentrations were significantly and positively related to bone metabolic marker levels in all patients, and the intact serum PTH concentrations were significantly and negatively related to BMD of lumbar spine in PHP patients. Conclusions: These results suggest that PTH stimulates bone turnover in PHP Ib patients, resulting in a relatively lower BMD in PHP Ib patients than in IHP+OHP patients. The present study indicates that bones of most cases of PHP could respond to PTH. European Journal of Endocrinology 144 263±269 Introduction This was believed to result from the same abnormality in cAMP generation occurring in bone tissue. In Pseudohypoparathyroidism (PHP) is a heterogeneous contrast, radiographic and histological findings (3±8), disease complex characterized by resistance of the in addition to diminished bone density (9) and increased proximal kidney tubule to the action of parathyroid serum alkaline phosphatase activity (10), have provided hormone (PTH) with or without typical features of evidence of excessive PTH action on bone in at least Albright's hereditary osteodystrophy (AHO) such as some patients with PHP. Furthermore, Murray et al. short stature, round face, brachydactyly, mental (11) and Ish-Shalom et al. (12) demonstrated that bone retardation and ectopic calcification (1). Biochemical cells from patients with PHP showed a normal cAMP characteristics are hypocalcemia, hyperphosphatemia, response to PTH. Although these findings suggest that increased immunoreactive PTH and a subnormal bones in some patients with PHP could respond to PTH, phosphaturic response to exogenous PTH associated no information is available on whether serum PTH with a blunted (PHP type I) or normal increase (PHP level is related to bone metabolic markers or to bone type II) in cyclic AMP (cAMP) excretion. Hypocalcemia mineral density (BMD) in patients with PHP. In this despite increased circulating PTH and subnormal study, we demonstrated that PTH could stimulate bone calcemic response to prolonged intramuscular PTH turnover in PHP patients, resulting in a relatively lower administration suggests the existence of skeletal BMD in patients with PHP than in patients with resistance in addition to renal resistance in PHP (2). idiopathic and postoperative hypoparathyroidism. q 2001 Society of the European Journal of Endocrinology Online version via http://www.eje.org Downloaded from Bioscientifica.com at 09/24/2021 12:43:25PM via free access 264 M Kanatani and others EUROPEAN JOURNAL OF ENDOCRINOLOGY (2001) 144 Table 1 Characteristics of patients with hypoparathyroidism. Group PHP Ia PHP Ib IHP OHP Number 2 8 5 14 Age (years) 47.5 43.3^6.1 50.2^5.6 49.9^4.6 Sex (M:F) 1:1 4:4 3:2 2:12 Serum calcium (mg/dl) 8.9 9.1^0.1 8.9^0.1 9.0^0.1 Serum phosphorus (mg/dl) 3.6 4.2^0.1 4.0^0.1 4.0^0.2 Serum creatinine (mg/dl) 0.9 0.9^0.2 0.9^0.2 0.9^0.1 Serum intact PTH (pg/ml) 22.5 95^31.9* 2.2^1.4 3.9^1.2 Serum 25(OH)D3 (mg/l) 10.7 19.5^2.7 21.6^3.5 14.9^3.2 ² Serum 1,25(OH)2D3 (ng/l) 23.1 15.3^4.8 47.9^17.4 ND ² Vitamin D therapy 1a(OH)D3 (mg/day) 1.25 2.06^0.14 2.80^0.25 1.80^0.10 Data are expressed as means ^ S.E.M. ND, not determined. *P , 0:05 compared with IHP+OHP; ²P , 0.05 compared with IHP. Study participants and methods patients without AHO were diagnosed as PHP type Ib. Gsa activity of the erythrocyte plasma membranes was Patients normal in all PHP type Ib patients (Table 2). All patients had been receiving active vitamin D3 This study was carried out in a total of 29 patients. Five treatment for more than 3 years to maintain normal of these patients (two women and three men; age serum concentrations of calcium and phosphorus. Each 50:2 ^ 5:6 years) had idiopathic hypoparathyroidism patient was receiving an unrestricted diet as an (IHP), 14 (12 women and two men; age 49:9 ^ 4:6 outpatient. Supplementary oral calcium, phosphate- years) had postoperative hypoparathyroidism (OHP; binding antacids, or thiazide diuretics were not serum intact PTH ,15 ng/l), two (one woman and one prescribed for any of the patients studied. This study man; mean age 47.5 years) had PHP Ia, and eight (four was approved by the Institution Review Board of Kobe women and four men; age 43:3 ^ 6:1 years) had PHP University School of Medicine. Informed consent was Ib. The clinical data and therapy during the study are obtained from all patients. shown in Table 1. The diagnosis of PHP was based on clinical symptoms, hypocalcemia, hyperphosphatemia, serum concentrations of intact PTH, and increases in Measurement of erythrocyte membrane Gsa urinary phosphate and cyclic AMP in response to exogenous PTH (13) (Table 2). Two of the ten patients activity with PHP had Albright's hereditary osteodystrophy We measured Gsa activity in the erythrocyte mem- (AHO) and were diagnosed as PHP type Ia. Gsa activity brane by assessing the ability of cholera toxin to of the erythrocyte plasma membranes was 40% of the catalyze 32P-ADP ribosylation of the 42 000 dalton a control value in one of the two PHP type Ia patients, subunit of Gs. Human erythrocyte ghosts were and 58% in the other (Table 2). The other eight PHP prepared by the method of Ikeda et al. (14), with a Table 2 Renal responses to rapid infusion of PTH1-34 and erythrocyte membrane Gsa activity in PHP patients. Ellsworth±Howard test Patient Age Gsa activity no. (years) Sex AHO DUrinary cAMP (mmol/h) DUrinary Pi (mmol/2 h) (% of standard) 1 36 F (+) 0.03 0.63 40 2 59 M (+) 0.21 1.06 58 323M(2) 0.02 0.37 105 440M(2) 0.23 0.48 110 545F(2) 0.41 0.73 108 652F(2) 0.33 0.91 98 749F(2) 0.80 0.06 110 875M(2) 0.35 0.19 99 943M(2) 0.29 0.41 106 10 19 F (2) 0.01 0.34 103 Normal range .1 .1.13 Pi, inorganic phosphate. www.eje.org Downloaded from Bioscientifica.com at 09/24/2021 12:43:25PM via free access EUROPEAN JOURNAL OF ENDOCRINOLOGY (2001) 144 PTH responsiveness of bone in PHP 265 slight modification. The ghosts were recovered in a final quantified by HPLC using a fluorescence detector, as volume of 3 ml at 2±3 mg of protein/ml. Cholera toxin reported previously (19). In brief, after urine samples (250 mg/ml) and islet-activating protein (50 mg/ml) were hydrolysed with HCl, they were ultrafiltrated and were preincubated for 15 min at 37 8C. Twenty applied to CF1 cellulose columns. The samples were microliters ghost, 20 ml preincubated Cholera toxin eluted from the cellulose columns with distilled water, or islet-activating protein and 60 ml reaction mixture and pyridinium cross-links were separated by reversed- were activated for 10 min at 30 8C. The reaction phase HPLC and detected by fluorophotometry. The mixture contained 5 mmol/l HEPES, 0.5 mmol/l EDTA- intra- and interassay variations for total Pyr were 3.5 Na, 1 mmol/l ATP, 10 mmol/l thymidine, 100 mmol/l and 9.1% respectively, and those for total D-Pyr were potassium phosphate buffer (pH 8.0), 4 mmol/l GTP, 7.5% and 10.1% respectively. The sensitivity of the assays 32 100 mmol/l [ P]NAD, 5mmol/l MgCl2, and 1mmol/l is 1.66 nmol/l for both Pyr and D-Pyr. Serum tartrate- dithiothreitol. Incubations were terminated by dilution resistant acid phosphatase (TRAP) activity was deter- with 2.5 ml ice-cold 5 mmol/l Tris±HCl (pH 7.5) and mined by measuring the absorbance of 2,6-dichloro-4- centrifuged at 27 000 g for 15 min.