Unique and common genetic effects between bone mineral density and calcaneal quantitative ultrasound measures: the Fels Longitudinal Study.

Introduction: Areal bone mineral density (BMD) and calcaneal quantitative ultrasound (QUS) measures are correlated, and both traits predict osteoporotic fracture risk independently. However, few studies have examined whether common genetic effects (i.e., pleiotropy) exist between these traits in extended families. In this study, we estimated the additive genetic correlation and random environmental correlation between BMD measured at various skeletal sites and calcaneal QUS measures.

Methods: Our sample included 537 adults (251 men and 286 women) from 110 families participating in the Fels Longitudinal Study. Total hip, femoral neck, lumbar spine, and total body BMD were measured using dual energy X-ray absorptiometry. Three measures of calcaneal structure--broadband ultrasound attenuation (BUA), speed of sound (SOS), and quantitative ultrasound index (QUI)--were collected from the non-dominant heel using the Sahara sonometer. Applying a variance components-based maximum likelihood method, we estimated the heritability of each trait and estimated the genetic and environmental correlations between the different BMD and QUS measures.

Results: Heritability estimates were significant for all measures of BMD and QUS ranging from 0.55 to 0.78. Significant non-zero genetic correlations were found between the different BMD and QUS measures. All genetic correlations were also significantly different from 1. Genetic correlations between total hip BMD and each of the QUS measures were 0.63 with BUA, 0.50 with SOS, and 0.56 with QUI. For femoral neck BMD, genetic correlations were similar to those between total hip BMD and QUS measures. Genetic correlations between BMD of the lumbar spine and QUS measures ranged from 0.34 to 0.38, and those between total body BMD and QUS measures, from 0.51 to 0.54. In contrast, all random environmental correlations were not significantly different from zero.

Conclusion: This study demonstrates that BMD and calcaneal QUS measures among healthy men and women are significantly heritable and are, in part, jointly influenced by a common set of underlying genes. Additionally, this study also provides evidence for a unique set of genes that independently influences each individual trait.