Factors associated with vertebral fracture risk in patients with primary hyperparathyroidism

Objective: To examine factors, in addition to bone mineral density (BMD), such as the common calcium-sensing receptor (CASR) gene polymorphisms, associated with vertebral fracture (VFx) risk in primary hyperparathyroidism (PHPT). Design and methods: A cross-sectional analysis of 266 Caucasian PHPT seen as outpatients. Serum calcium (sCa) phosphate metabolism parameters were measured. BMD was assessed by dual-energy X-ray absorptiometry (expressed as Z-score) at lumbar spine (Z-LS) and femoral neck, morphometric VFx by radiograph, and CASR A986S/R990G genotypes by PCR amplification and genomic DNA sequencing. Results: Fractured patients (n=100, 37.6%) had lower sCa (10.8 +/- 0.7 mg/dl) and Z-LS BMD (-1.0 +/- 1.44), higher age (61 +/- 10 years), and prevalence (51%) of >= 1 S alleles of the CASR A986S single-nucleotide polymorphism (SNP; AS/SS), than those not fractured (n=166, 11.2 +/- 1.0 mg/dl, -0.57 +/- 0.97, 58 +/- 13 years, and 38% AS/SS, respectively, P < 0.05 for all comparisons). Logistic regression, with VFx as dependent variable, showed independent risks associated with increased age (OR 1.03, 95% CI 1.01-1.06, P=0.006), decreased sCa (OR 1.86, 95% CI 1.28-2.7, P=0.001), and Z-LS BMD (OR 1.4, 95% CI 1.12-1.7, P=0.002) and presence of AS/SS (OR 1.8, 95% CI 1.1-2.9, P=0.05). The presence of two out of three factors (age >= 58 years, sCa < 10.8 and Z-LS BMD% -1.0, and AS/SS genotype) gave an overall OR of 4.2 (95% CI 2.25-7.85, P < 0.0001). Conclusions: In PHPT, VFx is associated positively with age, negatively with sCa and spinal BMD, and presence of at least one copy of the CASR A986S SNP.