Chromosomal regions harboring genes for the work to femur failure in mice.

The work to failure is defined as the maximum energy bone can absorb before breaking, and therefore is a direct test of the risk of fracture. To determine the genetic loci influencing work to failure, we have performed a high density genome-wide scan in 633 (MRL x SJL) F(2) female mice. Five loci ( P<0.005) with significant effects on work to failure were found on chromosomes 2, 7, 8, 9, and X, which collectively explained around 20% variance of work to femur failure in F(2) mice. Of those, only the QTL on chromosome 9 was concordant with bone mineral density (BMD) QTLs. Eight significant interactions ( P<0.01) between marker loci were identified, which accounted for an equivalent amount of F(2) variance (23%) to combined single QTL effects. Our results demonstrate that most of the genetic loci regulating work to failure are different from those for BMD in the 7-week-old female mice. If this is also true in humans, this finding will challenge the predictive value of BMD for the risk of fracture.