Genetic determination of variation and covariation of peak bone mass at the hip and spine

The likelihood of low trauma fracture in the elderly is highly predictable by peak bone mass (PBM) at age similar to 25-50 yr. We estimated the magnit ude of genetic determination of the variation and covariation of PBM of the spine and hip (adjusted by age, gender, and ethnicity) in 47 independent h ealthy full-sib pairs and 27 healthy mother-offspring pairs. For the spine and hip, the narrow-sense heritabilities (h(2)) (mean +/- SE) were 0.76 +/- 0.34 and 0.84 +/- 0.36, respectively, when estimated from full sibs, and 0 .86 +/- 0.38 and 0.84 +/- 0.39, respectively, when estimated from parent-of fspring. Some genetic loci underlying PBM variation at the hip and spine ar e the same or closely linked, as is reflected by the high genetic correlati on of 0.95 +/- 0.05 between them when estimated from full sibs, and 0.57 +/ - 0.27 when estimated from parent-offspring, respectively. Generally, commo n familial environmental effects shared by relatives may bias these estimat es. However, these effects may be small, since our results reported herein and those in other earlier studies indicate that common familial environmen tal effects are probably negligible in causing similarity of bone mass amon g family members. The correlation of bone mass among randomly sampled coupl es living in the same household is small and nonsignificant as measured eit her by densitometry at the radius and ulna or by quantitative ultrasound at the patella. The problem of shared environmental effects notwithstanding, we conclude that much of the PBM Variation and covariation at the hip and s pine is determined genetically.