Genetic markers, bone mineral density, and serum osteocalcin levels

We evaluated five genetic markers for products that contribute to skeletal mineralization including the Sp1 polymorphism for type I collagen Ai (COLIA1), the vitamin D receptor (VDR) translation initiation site polymorphism, the promoter of the osteocalcin gene containing a C/T polymorphism, the estrogen receptor (ER) gene containing a TA repeat, and the polymorphic (AGC)n site in the androgen receptor. These markers were evaluated for their potential relationship with bone mineral density (BMD), measured by dual-energy X-ray densitometry, or its 3-year change. Additionally, potential associations of these genotypes and with baseline osteocalcin concentration or its 3-year change (assessed using radioimmunoassay) were evaluated. The study was conducted in 261 pre- and perimenopausal women of the Michigan Bone Health Study, a population-based longitudinal study of musculoskeletal characteristics and diseases. The polymorphic (AGC)n site in the androgen receptor showed a strong association with BMD of the femoral neck (FN) and lumbar spine and remained highly significant after adjusting for body mass index (BMI), oophorectomy/hysterectomy, oral contraceptive (OC) use and hormone replacement use (p < 0.001). The TA repeat at the 5' end of the ER gene was associated with total body calcium (p < 0.05) after adjusting for BMI, oophorectomy and hysterectomy, and OC use. The frequency of oophorectomy and hysterectomy within selected genotypes explained much of the statistically significant association of the ER genotypes with BMD of the FN and spine. There was no association of measures of BMD or bone turnover with the Sp1 polymorphism for COLIA1, the VDR translation initiation site polymorphism, or the C/T promoter polymorphism of the osteocalcin gene. These findings suggest that sex hormone genes may be important contributors to the variation in BMD among pre- and perimenopausal women.