Vitamin D Receptor Gene Polymorphisms and Bone Mineral Homeostasis

Abstract

Osteoporosis is a systemic skeletal disease characterized by a reduced bone mineral mass and a deterioration of bone tissue microarchitecture, with a consequent increased bone fragility and a higher risk of fracture (1). The latter also depends on factors unrelated to bone mineral mass itself. In the search for “osteoporosis genes,” it is important to keep in mind that bone mineral mass is a complex notion that maybe variably appreciated by different techniques. Actually, various parts of the skeleton are characterized by different proportions of spongious and compact bone, and thereby by different turnover rates. Whole body bone mineral mass can be measured. For this purpose, a variety of techniques based on the attenuation by bony tissue of either a photon radiation (dual X-ray absorptiometry [DXA], single photon absorptiometry [SPA] or ultrasonic energy) have been used. X-ray attenuation-based methods provide information on bone mineral content (BMC, in grams of hydroxyapatite equivalent) and areal bone mineral density (aBMD, in grams of hydroxyapatite equivalent per unit of bone scanned area). The latter integrates the notion of bone mineral mass and an adjustment for outer bone dimensions as determined in a plan perpendicular to the radiation beam direction (2). Besides, volumetric bone mineral density (grams per cubic square of bone tissue) can be assessed by quantitative computerized tomography (QCT), or indirectly estimated from results obtained with the DXA technology. Consequently, although it is presently unknown whether the same set of genes influences both cortical and spongious bone, the association of a single gene locus, which can by essence determine only one bone mineral mass constituent, with any of the measures of “bone mass” defined previously, will be burdened by a degree of imprecision proportional to the number and magnitude of genetic effects on the other constituents of bone mineral mass.KeywordsBone Mineral DensityBone MassCalcium IntakeDietary Calcium IntakeAllelic PolymorphismThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.