INFLUENCE OF VITAMIN-D-RECEPTOR GENOTYPE ON BONE-MINERAL DENSITY IN POSTMENOPAUSAL WOMEN - A TWIN STUDY IN BRITAIN

Objectives-To investigate the possible association between vitamin D r eceptor genotype and bone mineral density in a large group of postmeno pausal twins. Design-Cross sectional twin study. Setting-Twin populati on based in Britain. Subjects-95 dizygotic (non-identical) pairs of tw ins and 87 monozygotic (identical) pairs of twins aged 50-69 years, po stmenopausal, and free of diseases affecting bone, recruited from a na tional register of twins and with a media campaign. Main outcome measu res-Bone mineral density measured at the hip, lumbar spine, forearm, a nd for the whole body by dual energy x ray absorptiometry in relation to differences in the vitamin D receptor genotype. Results-At all site s the values of bone density among dizygotic twins were more similar i n those of the same vitamin D receptor genotype than in those of diffe ring genotype, and the values in the former were closer to the correla tions seen in monozygotic twins. Women with the genotype that made the m at risk of osteoporotic fracture had an adjusted bone mineral densit y that was significantly lower by SD 0.5 to 0.6 at the hip, lumbar spi ne, and for the whole body, The results could not be explained by diff erences in age, weight, years since menopause, or use of hormone repla cement therapy. Conclusions-The findings that in postmenopausal women in Britain bone density-particularly at the hip and spine-is genetical ly linked and specifically associated with the vitamin D receptor geno types should lead to novel approaches to the prevention and treatment of osteoporosis.