Both LRP5 and LRP6 genes have been implicated to play a role in bone metabolism. In a large population-based study, we related common variation in both genes to bone parameters and fractures. LRP5 variation was associated to both BMD and frame size, whereas both LRP5 and 6 variations were associated with an increased fracture risk in males. Introduction: The low-density lipoprotein receptor-related protein 5 (LRP5) gene has a clear role in rare BMD traits and also in normal variation in peak BMD. We examined whether common variation in LRP5 and its close homolog, LRP6, plays a role in BMD in old age and fractures, the main clinical endpoint of osteoporosis. Materials and Methods: We analyzed four variants of LRP5 and one amino acid variant of the LRP6 gene in a large prospective population-based cohort study of elderly subjects. Results and Conclusions: In men, the LRP5 1330-valine variant was associated with decreased BMD at the lumbar spine and the femoral neck with evidence for an allele-dose effect (p = 0.001 and 0.01, respectively). The Val allele was also associated with decreased vertebral body size and femoral neck width. Haplotype analysis of studied polymorphisms did not improve the association found and suggested that the 1330 variant was driving the association. We observed a borderline significant association of the LRP6 Ile1062Val polymorphism with height and vertebral body size in males. Male carriers of the LRP5 1330-valine variant had a 60% increased risk for fragility fractures, and the LRP6 1062-valine allele also conferred a 60% higher risk. Carriers of both the risk alleles of LRP5 and 6 had a 140% (p = 0.004) higher risk compared with noncarriers of both risk alleles and accounted for 10% of the fractures in males. The fracture risks were independent of age, height, weight, and BMD. In women, all of these associations were weaker and less consistent compared with men. The polymorphisms that were found associated were both situated in potentially important domains of the receptor and show considerable evolutionary conservation, which is evidence for functional importance of these residues.

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Journal of Bone and Mineral Research
Erasmus MC: University Medical Center Rotterdam