Two mutations of the Gsα gene in two Japanese patients with sporadic pseudohypoparathyroidism type Ia

Pseudohypoparathyroidism Ia (PHP-Ia), is an inherited disease with clinical hypoparathyroidism caused by parathyroid hormone resistance (PTH), and shows the phenotype of Albright hereditary osteodystrophy (AHO), including short stature, obesity, round face, brachydactyly, and subcutaneous ossification. This disease is caused by mutation that inactivates the α-subunit of Gs, the stimulatory regulator of adenylyl cyclase. Here, a novel frameshift mutation (delG at codon 88) in exon 4, and a missense mutation (R231H) in exon 9 of the Gsα gene were identified in two Japanese patients with sporadic PHP-Ia. Deletion of a G in exon 4 at codon 88 in the first patient produced a premature stop codon, resulting in the truncated protein. The second patient had a previously reported R231H mutation. Because this amino acid is located in a region, switch 2, that is thought to interact with the βγ subunit of Gsα protein, this mutation may impair Gs protein function. We report here one novel Gsα mutation, and note that mutations in Japanese patients with PHP-Ia are probably heterogeneous. Received: November 27, 2000 / Accepted: March 21, 2001     

Elevated serum IGF‐1 levels synergize PTH action on the skeleton only when the tissue IGF‐1 axis is intact

There is growing evidence that insulin‐like growth factor 1 (IGF‐1) and parathyroid hormone (PTH) have synergistic actions on bone and that part of the anabolic effects of PTH is mediated by local production of IGF‐1. In this study we analyzed the skeletal response to PTH in mouse models with manipulated endocrine or autocrine/paracrine IGF‐1. We used mice carrying a hepatic IGF‐1 transgene (HIT), which results in a threefold increase in serum IGF‐1 levels and normal tissue IGF‐1 expression, and Igf1 null mice with blunted IGF‐1 expression in tissues but threefold increases in serum IGF‐1 levels (KO‐HIT). Evaluation of skeletal growth showed that elevations in serum IGF‐1 in mice with Igf1 gene ablation in all tissues except the liver (KO‐HIT) resulted in a restoration of skeletal morphology and mechanical properties by adulthood. Intermittent PTH treatment of adult HIT mice resulted in increases in serum osteocalcin levels, femoral total cross‐sectional area, cortical bone area and cortical bone thickness, as well as bone mechanical properties. We found that the skeletal response of HIT mice to PTH was significantly higher than that of control mice, suggesting synergy between IGF‐1 and PTH on bone. In sharp contrast, although PTH‐treated KO‐HIT mice demonstrated an anabolic response in cortical and trabecular bone compartments compared with vehicle‐treated KO‐HIT mice, their response was identical to that of PTH‐treated control mice. We conclude that (1) in the presence of elevated serum IGF‐1 levels, PTH can exert an anabolic response in bone even in the total absence of tissue IGF‐1, and (2) elevations in serum IGF‐1 levels synergize PTH action on bone only if the tissue IGF‐1 axis is intact. Thus enhancement of PTH anabolic actions depends on tissue IGF‐1. © 2010 American Society for Bone and Mineral Research.     

Parathyroid hormone (PTH)–induced bone gain is blunted in SOST overexpressing and deficient mice

Intermittent parathyroid hormone (PTH) treatment is a potent bone anabolic principle that suppresses expression of the bone formation inhibitor Sost. We addressed the relevance of Sost suppression for PTH‐induced bone anabolism in vivo using mice with altered Sost gene dosage. Six‐month‐old Sost overexpressing and 2‐month‐old Sost deficient male mice and their wild‐type littermates were subjected to daily injections of 100 µg/kg PTH(1–34) or vehicle for a 2‐month period. A follow‐up study was performed in Sost deficient mice using 40 and 80 µg/kg PTH(1–34). Animals were sacrificed 4 hours after the final PTH administration and Sost expression in long bone diaphyses was determined by qPCR. Bone changes were analyzed in vivo in the distal femur metaphysis by pQCT and ex vivo in the tibia and lumbar spine by DXA. Detailed ex vivo analyses of the femur were performed by pQCT, µCT, and histomorphometry. Overexpression of Sost resulted in osteopenia and Sost deletion in high bone mass. As shown before, PTH suppressed Sost in wild‐type mice. PTH treatment induced substantial increases in bone mineral density, content, and cortical thickness and in aging wild‐type mice also led to cancellous bone gain owing to amplified bone formation rates. PTH‐induced bone gain was blunted at all doses and skeletal sites in Sost overexpressing and deficient mice owing to attenuated bone formation rates, whereas bone resorption was not different from that in PTH‐treated wild‐type controls. These data suggest that suppression of the bone formation inhibitor Sost by intermittent PTH treatment contributes to PTH bone anabolism. © 2010 American Society for Bone and Mineral Research     

IL21R and PTH may underlie variation of femoral neck bone mineral density as revealed by a genome‐wide association study

Bone mineral density (BMD) measured at the femoral neck (FN) is the most important risk phenotype for osteoporosis and has been used as a reference standard for describing osteoporosis. The specific genes influencing FN BMD remain largely unknown. To identify such genes, we first performed a genome‐wide association (GWA) analysis for FN BMD in a discovery sample consisting of 983 unrelated white subjects. We then tested the top significant single‐nucleotide polymorphisms (SNPs; 175 SNPs with p < 5 × 10^?4) for replication in a family‐based sample of 2557 white subjects. Combing results from these two samples, we found that two genes, parathyroid hormone (PTH) and interleukin 21 receptor (IL21R), achieved consistent association results in both the discovery and replication samples. The PTH gene SNPs, rs9630182, rs2036417, and rs7125774, achieved p values of 1.10 × 10^?4, 3.24 × 10^?4, and 3.06 × 10^?4, respectively, in the discovery sample; p values of 6.50 × 10^?4, 5.08 × 10^?3, and 5.68 × 10^?3, respectively, in the replication sample; and combined p values of 3.98 × 10^?7, 9.52 × 10^?6, and 1.05 × 10^?5, respectively, in the total sample. The IL21R gene SNPs, rs8057551, rs8061992, and rs7199138, achieved p values of 1.51 × 10^?4, 1.53 × 10^?4, and 3.88 × 10^?4, respectively, in the discovery sample; p values of 2.36 × 10^?3, 6.74 × 10^?3, and 6.41 × 10^?3, respectively, in the replication sample; and combined p values of 2.31 × 10^?6, 8.62 × 10^?6, and 1.41 × 10^?5, respectively, in the total sample. The effect size of each SNP was approximately 0.11 SD estimated in the discovery sample. PTH and IL21R both have potential biologic functions important to bone metabolism. Overall, our findings provide some new clues to the understanding of the genetic architecture of osteoporosis. © 2010 American Society for Bone and Mineral Research     

老年人血清PTH RIA及其临床意义

应用放射免疫法对８１例健康老年人和２４８例非甲状腺疾病的老年患者进行甲状旁腺激素（ＰＴＨ）的测定。结果表明健康老人血清ＰＴＨ含量明显高于正常（ｐ〈０．０１）,其中女性差异十分显著（ｐ〈０．０１）。老年高血压、肿瘤、糖尿病、脑梗塞、慢性肾衰、肺炎与老年健康组相比差异十分显著（ｐ〈０．０１）。它可以作为观察和诊断甲状旁腺功能异常、钙代谢紊乱等多种疾病的依据。同时可以通过对老年人钙剂补充来改善甲状旁腺功     

Humoral and ionic regulation of osteoclast acidity

Summary Regulation of the acidity of osteoclasts was determinedin situ on the endocranial surfaces of mouse calvaria using acridine orange, a fluorescent weak base. Osteoclasts could be identified by (1) large size, (2) multiple nuclei, (3) relatively small numbers of cells, and (4) the way and the extent to which they took up the dye. Nonosteoclastic cells were stained mainly in their nuclei and occasionally in a few lysosomes surrounding their nuclei, which were uniformly single in nonosteoclasts. Nuclei in osteoclasts were also stained, but the staining of the nuclei was partially masked by the intensity and completeness of the staining of the cytoplasm. In some cells the cytoplasmic staining appeared to be in discrete granules, giving the cytoplasm a bright, frothy appearance. This fluorescence was present in both treated and untreated cells and aided in identifying the osteoclasts. Acridine orange fluorescence at 624 nm intensity, and hence, osteoclast acidity, was increased by parathyroid hormone and prostaglandin E₂. Parathyroid hormone-induced increases in acidity were inhibited by calcitonin, cortisol, sodium fluoride, and prostaglandin E₂. Furthermore, osteoclast acidity was dependent largely or partially on (1) maintenance of K⁺ and Na⁺ gradients, (2) patent Na⁺ channels, (3) chloride-bicarbonate exchange, and (4) H⁺, K⁺-ATPase. These findings demonstrate that osteoclasts become acidified by mechanisms similar to those occurring in gastric parietal cells.     

The effect of 1,25 dihydroxycholecalciferol on parathyroid hormone secretion by monolayer cultures of bovine parathyroid cells

Summary Controversy exists over a direct effect of 1,25(OH)₂D₃ on PTH secretion. To investigate the possibility that the suppressive effect of 1,25(OH)₂D₃ on PTH secretion may be demonstrable in 1,25(OH)₂D₃-depleted tissue and/or after prolonged periods of exposure to 1,25(OH)₂D₃, primary monolayer cultures of bovine parathyroid cells were established in 1∶1 DMEM/Ham's F-12 media supplemented with 2% calf serum but not 1,25(OH)₂D₃. Ionized calcium was maintained at 1.0 mM. Experiments were performed on 4-day-old culture cells. PTH concentration was measured using both a mid-region/carboxyl and an amino-terminal PTH antisera. 1,25(OH)₂D₃ at a concentration of 0.1 ng/ml suppressed PTH secretion by 32±7% after 48 hours. High calcium concentration (2.0 mM) suppressed PTH secretion by 37±10% and this effect was not additive over that of 1,25(OH)₂D₃. PTH secretion rate recovered fully 48 hours after normalization of the external calcium concentration but not after the removal of 1,25(OH)₂D₃. It is concluded that 1,25(OH)₂D₃ directly suppresses PTH secretion by monolayer culture of bovine parathyroid cells.     

Verapamil increases serum ionized calcium and serum phosphate in patients with post-surgical hypoparathyroidism

The calcium homeostasis in eight patients with postoperative hypoparathyroidism was examined before and after 2 weeks of administration of verapamil in an oral dose of 80 mg three times daily. Serum ionized calcium increased during verapamil treatment (from mean +/- SD of 1.10 +/- 0.06 to 1.24 +/- 0.38 mmol l-1; P less than 0.05), as well as total serum calcium corrected for protein (from 2.11 +/- 0.13 to 2.18 +/- 0.13 mmol l-1; P less than 0.05). During treatment with verapamil there was an increase in serum phosphate (from 1.08 +/- 0.15 to 1.19 +/- 0.20 mmol l-1 P less than or equal to 0.05) and in the urinary excretion of phosphate (P/creatinine ratio from 1.22 +/- 0.69 to 1.83 +/- 0.97; P less than or equal to 0.05). The serum 1,25-dihydroxyvitamin-D3 and serum parathyroid hormone were below the detection limits both before and after verapamil treatment. There were no significant changes either of the intestinal absorption of calcium or of the urinary calcium excretion. Serum osteocalcin was insignificantly reduced after treatment (1.60 +/- 0.70 before treatment and 1.25 +/- 0.71 micrograms l-1 after treatment). Thus in patients with post-surgical hypoparathyroidism verapamil has effects on calcium and phosphorous homeostasis. Since calcium absorption was not influenced by verapamil, it is suggested that verapamil affects bone mineral metabolism.     

血清PTH—M测定诊断271例慢性肾衰致继发性甲状旁腺功能亢进

目的：探讨血清甲状旁腺激素Ｍ（ＰＴＨＭ）含量测定对诊断慢性肾功能衰竭（ＣＲＦ）导致的继发性甲状旁腺功能亢进（ＳＨＰ）的临床价值和意义。方法：利用双抗放射免疫测定法对２７１例ＣＲＦ患者作血ＰＴＨＭ含量测定。结果：约８６％的患者血ＰＴＨＭ含量＞２７ｎｇ／ｄｌ的正常参考水平，其中约２５％的患者血ＰＴＨＭ含量＞２００ｎｇ／ｄｌ。血ＰＴＨＭ含量和患者的年龄或性别不存在相关性，但血ＰＴＨＭ含量和患者经历血液透析年限呈正相关（ｒ＝０６００）。结论：血ＰＴＨＭ测定对诊断ＳＨＰ有重要的临床价值，并对ＳＨＰ的监测有一定的参考价值。     

Ursodeoxycholic Acid Enhances Fractional Calcium Absorption in Primary Biliary Cirrhosis

Bone disease is a frequently reported complication in primary biliary cirrhosis (PBC), but its pathogenesis is poorly understood. Calcium malabsorption has been considered as an important contributing factor. Ursodeoxycholic acid (UDCA) is the treatment of choice in PBC, improving survival, but its effect on calcium absorption is unknown. In this study, we have measured fractional calcium absorption, using a single isotope method, in a group of female PBC patients (median age: 60 years, range: 46–78 years) and age-matched female controls (median age: 58 years, range: 36–74). Bone mineral density (BMD) in PBC patients was significantly lower than age-matched controls (g/cm²± SEM; lumbar spine: controls 1.139 ± 0.028, PBC patients 1.004 ± 0.026, p= 0.0028; femoral neck: controls 0.944 ± 0.034, PBC patients 0.819 ± 0.023, p = 0.0032). Twenty two PBC patients, who were not vitamin D-deficient, were off and on UDCA for ~1 month and ~8 weeks, respectively. Fractional calcium absorption in PBC patients prior to UDCA treatment (mean ± SEM, 33.8 ± 2.6%) was significantly lower than controls (52.0 ± 2.4%, p<0.001). Following UDCA therapy, fractional calcium absorption increased significantly (Off UDCA: 33.1 ± 2.6%, On UDCA: 36.6 ± 2.5%, p<0.0058). Osteocalcin levels were significantly raised in the PBC group (mean ± SEM, ng/ml, 41.4 ± 2.02) compared to controls (31.1 ± 2.64, p= 0.002). There were no differences in parathyroid hormone (PTH) or 25-hydroxyvitamin D levels between these two groups or following UDCA therapy. In conclusion, we found that PBC patients display low spinal and femoral neck BMD, reduced fractional calcium absorption, and elevated plasma osteocalcin. The calcium malabsorption is corrected partially by UDCA therapy. Long-term studies are required to determine whether this effect can be sustained, and whether a sustained increase in fractional calcium absorption can translate into a favorable change in bone strength in patients with PBC. Received: 27 November 2001 / Accepted: 11 April 2002