title: Do genetic factors explain associations between muscle strength, lean mass, and bone density? A twin study.
abstract: Are the associations between muscle strength, lean mass, and bone mineral density (BMD) genetically determined? Based on within-pair differences in 56 monozygotic (MZ) and 56 dizygotic (DZ) female twin pairs, mean age 45 yr (range 24-67), BMD was associated with lean mass, independent of fat mass and height (P < 0.05). A 10% increment in femoral neck (FN) BMD was associated with a 15% increment in lean mass (approximately 6 kg). BMD was associated with muscle strength (measured in 35 pairs) before, but not after, adjusting for lean mass. Based on age-adjusted cross-sectional analyses, same-trait correlations (+/- SE) in MZ pairs were double those in DZ pairs: FN BMD (0.62 +/- 0.08, 0.33 +/- 0.12) and lean mass (0.87 +/- 0.03, 0.30 +/- 0.11; all P < 0.001), consistent with a genetic hypothesis. The cross-trait correlation (r) between lean mass and FN BMD in the same individual was 0.43 +/- 0.06. The cross-trait cross-twin correlation between lean mass in one twin and FN BMD in the other was 0.31 +/- 0.07 in MZ pairs, approximately 75% of the cross-trait correlation (r) and 0.19 +/- 0.09 in DZ paris (P < 0.001). After adjusting for height and fat mass, the MZ and DZ cross-trait cross-twin correlations were no different (0.16 +/- 0.08 and 0.13 +/- 0.09, respectively). Therefore, genetic factors account for 60-80% of the individual variances of both FN BMD and lean mass, and > 50% of their covariance. The association between greater muscle mass and greater BMD is likely to be determined by genes regulating size.
authors.affiliation: Department of Medicine, Austin Hospital and Repatriation Medical Center, Melbourne, Australia.
authors.forename: E
authors.initials: E
authors.lastname: Seeman
authors.forename: J L
authors.initials: JL
authors.lastname: Hopper
authors.forename: N R
authors.initials: NR
authors.lastname: Young
authors.forename: C
authors.initials: C
authors.lastname: Formica
authors.forename: P
authors.initials: P
authors.lastname: Goss
authors.forename: C
authors.initials: C
authors.lastname: Tsalamandris
mesh_terms: D000328:Adult; D000368:Aged; D001823:Body Composition; D001827:Body Height; D015519:Bone Density; D004777:Environment; D005260:Female; D006801:Humans; D008875:Middle Aged; D009132:Muscles / Q000502:physiology*; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*