Bone ageing: genetics versus environment

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Abstract
Bone ageing results from a complex interaction between genetic and environmental factors (such as diet, climate and physical exercise) throughout human life. According to current literature, the most popular measures of bone ageing are osseometric measurements (OSM), bone mineral density (BMD) and osseographic scores (OSS), based on descriptive criteria of bone age. Plain roentgenography allows simultaneous assessment of all three measures. Ethnic differences with regard to these bone ageing characteristics have prompted us to study to the process anew, with the aim of elucidation the nature of the genetic and environmental components involved, and the possible interaction(s) between them. Despite abundant data on ethnic differences regarding these measures, modern knowledge on the genetics of these processes has derived primarily from the family studies of BMD, which pointed to strong involvement of the familial factors on bone mass. Segregation analysis performed by us in two ethnically different samples of pedigrees revealed a significant effect of the putative major gene on BMD of both compact and cancellous bone. The major finding of our bivariate segregation analysis was that it lead to the acceptance of the hypothesis predicating a single major locus with pleiotropy to both cancellous and compact BMD, but clearly rejecting the polygenic hypotheses. Our study of cortical index (CI) provided evidence that a single potential major gene controls not only the baseline trait level, but also the age at onset of the involutive bone changes, and the rate of the CI change with age. When we examined the environmental vs genetic influences on OSS variation in 32 human populations, we found very little environmental effect on the rate of bone change (r2 = 0.107), but a substantial effect on this rate of the genetic differences between populations (r = 0.480). Clarification of the genetic basis of bone ageing could have wide-ranging applications in the prevention and treatment of bone degenerative diseases such as osteoporosis and osteoarthritis, before irreversible damage takes place. There is thus a need to target the genetic analysis of BMD and the biochemical regulating factors of bone turnover through the use of molecular genetic techniques.