Genetic and environmental correlations between bone formation and bone mineral density: a twin study

Area of Science:

• Genetics
• Bone Biology
• Twin Studies

Background:

• Bone mineral density (BMD) and bone turnover are heritable traits.
• The relationship between genetic and environmental control of bone turnover and BMD is not fully understood.
• Bone specific alkaline phosphatase (BSAP) is an index of bone turnover.

Purpose of the Study:

• To investigate the relative contributions of genetic and environmental factors to BSAP.
• To examine the extent of common genetic regulation between BSAP and BMD.
• To assess shared environmental influences on BSAP and BMD.

Main Methods:

• Studied 97 female twin pairs (48 monozygotic, 49 dizygotic).
• Measured BSAP using radioimmunometric assay and BMD at the lumbar spine (LS) and femoral neck (FN) via dual-energy X-ray absorptiometry.
• Analyzed twin resemblance using intraclass correlation coefficients and genetic/environmental components via univariate and multivariate genetic models.

Main Results:

• BSAP levels were significantly higher in postmenopausal women compared to premenopausal women.
• BSAP and BMD were negatively correlated in cross-sectional analysis.
• Heritability estimates were 63% for BSAP, 77% for LS-BMD, and 72% for FN-BMD.
• Genes influencing BSAP accounted for 16% of LS-BMD genetic variance and 4% of FN-BMD genetic variance.
• No evidence for shared environmental factors influencing BSAP and BMD.

Conclusions:

• BSAP and BMD are independently heritable traits.
• Genetic factors influencing BSAP and BMD are largely distinct.
• Shared environmental factors do not significantly influence both BSAP and BMD.