[The determination of BB genotype of vitamin D receptors identifies patients at risk for osteoporosis].

The gene responsible for peak bone mass has been recently identified as the gene coding for the Vitamin D Receptor (VDR); there exist two alleles, termed "B" and "b", determining a typical allelic polymorphism. We determined the VDR genotype of 50 young post-menopausal women (mean age: 56 years), and measured bone density by Dual Energy X ray Absorptiometry (DEXA) twice: at the beginning of the study and after one year. VDR genotype was determined using the DNA extracted from hair cells, thus avoiding the use of blood samples. The frequency of VDR genotypes (BB or bb homozygous; Bb heterozygous) was approximately the same in the two groups of subjects (i.e., normal controls and osteoporotic women). The bone density of normal subjects (36) was measured for the second time one year after the first measurement. All BB homozygous subjects showed significantly decreased bone density values; 50% of them showed values below 0.750 g/cm2 at the second measurement, thus being classified as osteoporotic. However, neither bb homozygous nor Bb heterozygous subjects showed any significant decrease in bone density values (about 4% of the initial value). Therefore, determining the VDR genotype was critical for identifying the subjects who were normal at the first measurement, but had markedly decreased bone density values later, thus being at risk of developing osteoporosis.