The genetic, environmental and phenotypic correlations of bone phenotypes at the spine and hip in Chinese.

Background: Bone mineral density (BMD), bone mineral content (BMC), and bone size have been widely studied individually as important risk factors for osteoporotic fracture, but little is known about the correlation and the degree of sharing genetic and environmental factors between the pairs of the three phenotypes. Aim: The study investigated genetic correlation (p(G)), environmental correlation (p(E)) and phenotypic correlation (p(P)) between BMD, BMC and bone size. Subjects and methods: Bivariate variance decomposition analyses were performed in 904 subjects from 287 Chinese nuclear families. Results: Significant p(E), p(G) and p(P) were detected between BMD, BMC and bone size, except for p(E) between BMD and bone size at the hip (p(E) = 0.121, p = 0.361). Common shared genetic factors explained 86.1% and 60% of BMD and BMC genetic variations at the spine and hip, respectively. However, the genetic and environmental correlations between BMD and bone size were limited. p(E) and p(G) at the spine were 0.392 and 0.381, and at the hip were 0.121 and -0.205, respectively. Only 14.5% and 4.2% of variations between BMD and bone size at the spine and hip may be due to the shared genetic factors. Conclusion: The obtained results suggested that bone size may be used as another surrogate phenotype independently of BMD for eventual elucidation of the pathogenesis of osteoporosis because of the limited correlations between BMD and bone size.