Single Nucleotide Polymorphisms in Osteogenic Genes in Atrophic Delayed Fracture-Healing

Background: We propose that fracture-healing potential is affected by the patient's genome. This genotype is then phenotypically expressed by the patient at the time of injury. We examined the hypothesis that patients who exhibit delayed or impaired fracture-healing may have one or more single nucleotide polymorphisms (SNPs) within a series of genes related to bone formation. Methods: We performed a population-based, case-controlled study of delayed fracture-healing. Sixty-two adults with a long-bone fracture were identified from a surgical database. Thirty-three patients had an atrophic nonunion (delayed healing), and twenty-nine displayed normal fracture-healing. These patients underwent buccal mucosal cell harvesting. SNP genotyping was performed with use of bead array technology. One hundred and forty-four SNPs (selected from HapMap) within thirty genes associated with fracture-healing were investigated. Three SNPs did not segregate in the population and were excluded from the analysis. Eight of the remaining SNPs failed the test for Hardy-Weinberg equilibrium (p value smaller than the Bonferroni-corrected level of 0.05/141 = 0.000355) and were excluded. Results: Five SNPs on four genes were found to have a p value of <0.05 in the additive genetic model. Of these five significant SNPs, three had an odds ratio (OR) of >1, indicating that the presence of the allele increased the risk of nonunion. The rs2853550 SNP, which had the largest effect (OR = 5.9, p = 0.034), was on the IL1B gene, which codes for interleukin 1 beta. The rs2297514 SNP (OR = 3.98, p = 0.015) and the rs2248814 SNP (OR = 2.27, p = 0.038) were on the NOS2 gene coding for nitric oxide synthase. The remaining two SNPs had an OR of <1, indicating that the presence of the allele may be protective against nonunion. The rs3819089 SNP (OR = 0.26, p = 0.026) was on the MMP13 gene for matrix metallopeptidase 13, and the rs270393 SNP (OR = 0.30, p = 0.015) was on the BMP6 gene for bone morphogenetic protein 6. Conclusions: Variations in the IL1B and NOS2 genes may contribute to delayed fracture-healing and warrant further investigation.