The calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that has an extracellular bilobed venus flytrap domain (VFTD) predicted to contain five calcium (Ca(2+))-binding sites. To elucidate the structure-function relationships of the VFTD, we investigated 294 unrelated probands with familial hypocalciuric hypercalcaemia (FHH), neonatal severe primary hyperparathyroidism (NSHPT) or autosomal dominant hypocalcaemic hypercalciuria (ADHH) for CaSR mutations and performed in vitro functional expression studies and three-dimensional modelling of mutations involving the VFTD. A total of 70 different CaSR mutations were identified: 35 in FHH, 10 in NSHPT and 25 in ADHH patients. Furthermore, a CaSR variant (Glu250Lys) was identified in FHH and ADHH probands and demonstrated to represent a functionally neutral polymorphism. NSHPT was associated with a large proportion of truncating CaSR mutations that occurred in the homozygous or compound heterozygous state. Thirty-four VFTD missense mutations were identified, and 18 mutations were located within 10 Å of one or more of the predicted Ca(2+)-binding sites, particularly at the VFTD cleft, which is the principal site of Ca(2+) binding. Mutations of residues 173 and 221, which are located at the entrance to the VFTD cleft binding site, were associated with both receptor activation (Leu173Phe and Pro221Leu) and inactivation (Leu173Pro and Pro221Gln), thereby highlighting the importance of these residues for entry and binding of Ca(2+) by the CaSR. Thus, these studies of disease-associated CaSR mutations have further elucidated the role of the VFTD cleft region in Ca(2+) binding and the function of the CaSR.

. The number of vitamin D tests requested by primary care, and the associated cost, is rapidly increasing. . More cases of vitamin D deficiency were detected each year, but the odds of detecting deficiency decreased. . Repeat tests form a significant proportion of total requests, and should be performed after three to six months. . Seasonal variation in vitamin D levels should always be considered when requesting tests and interpreting results. Clinicians should consider risk factors for vitamin D deficiency to ensure targeted testing of patients. Why this matters to usThere is increasing awareness of the importance of vitamin D for maintaining musculoskeletal health by both the medical profession and the public. The number of requests for vitamin D testing from primary care is consequently increasing. Testing is expensive and can amount to a substantial financial burden, particularly if testing and retesting are performed inappropriately. There is a need to develop clear guidance for assessing vitamin D status in primary care. We believe our observations and recommendations will inform to improve the cost-effectiveness of vitamin D testing, its ability to influence management and thus make a real impact within primary care practice and patient care. Although this study was carried out in Liverpool, conclusions remain relevant to London given its greater black, Asian and minority ethnic population who are at increased risk of vitamin D deficiency.

Background: ApolipoproteinA1(apoA1) is the major apoprotein constituent of high-densitylipoprotein(HDL). The relationship of apoA1 -75 bp(M1 -) allele polymorphism with lipoprotein phenotype and cardiovascular diseae (CVD) remain unclear.

Context: Primary hyperparathyroidism (PHPT) is commonly associated with reduced bone mineral density (BMD) presenting with osteoporosis, increasing the risk of bone fragility fractures in these patients. Bisphosphonates, due to their anti-resorptive action, are known to improve the BMD and reduce the risk of bone fragility fractures. Therefore, bisphosphonates are considered as an alternative to surgical treatment in managing osteoporosis in PHPT patients. Aim: The aim of this observational study was to assess the effect of long term bisphosphonate therapy on BMD, bone fragility fracture and biochemical markers of bone metabolism in patients with PHPT. Methodology: Fifty patients (mean age 74 years) with PHPT who were treated with long term bisphosphonate therapy were studied retrospectively. The mean baseline (before commencing bisphosphonate therapy) BMD T-scores for lumbar spine (L2-L4) and left femoral neck were −2.5 and −2.1, respectively. Fourteen patients had bone fragility fractures before initiation of bisphosphonate therapy. Results: After an average of 5 years of bisphosphonate treatment, there was a significant increase in lumbar BMD T-score (−2.5 to −2.1, p = 0.013) and a non-significant change in left femoral neck BMD T-score (−2.1 to −2.2, p = 0.497). There was no increase in bone fragility fracture rate (p = 0.167). Serum corrected calcium reduced from 2.74 mmol/L to 2.60 mmol/L (p < 0.001) and urine calcium to creatinine ratio from 0.70 to 0.55 (p < 0.0001), both within the reference range. Conclusions: Our study suggests that long term bisphosphonate therapy improves lumbar BMD and prevents increase in bone fragility fracture rate. Additionally it improves hypercalcaemia in PHPT.

Background: Measurement of procollagen type I N-terminal propeptide (PINP) concentration in serum reflects the rate of type I collagen synthesis and can therefore be used as a bone formation marker. There are two methods of PINP quantification; the first measures the trimeric propeptide (intact PINP) and the second measures both the trimeric and monomeric propeptides (total PINP). Trimeric PINP is excreted via hepatic endothelial cells whereas monomeric PINP is cleared renally. Therefore in renal failure the total assay has a positive bias with respect to the intact assay, due to monomeric PINP accumulation. The aim of this study was to compare the performance of both assays across all stages of chronic kidney disease (CKD). Methods: Serum was taken from male (n=111) and female (n=105) patients attending a metabolic bone clinic and these were partitioned into stages of CKD 1-5. Each serum sample was analysed using the Roche electrochemiluminescence immunoassay for total PINP and the Immunodiagnostic Systems chemiluminescence immunoassay for intact PINP. Results: Passing-Bablok regression analysis comparing both methods showed that with advancing CKD there was a proportional positive bias affecting the total assay when compared to the intact assay. This proportional positive bias was statistically significant for CKD stages 3b, 4 and 5. Conclusions: Based on this method comparison study, usage of the total PINP assay should be avoided in CKD stages 3b, 4 & 5 (eGFR <u><</u>44 ml/min/1.73m²) and instead an intact assay used as the total assay overestimates PINP levels due to monomeric PINP accumulation.