The role of smoking status and collagen IX polymorphisms in the susceptibility to cervical spondylotic myelopathy

We investigated a possible association of collagen IX tryptophan (Trp) alleles (Trp2 and Trp3) and smoking with cervical spondylotic myelopathy (CSM) in 172 Chinese patients and 176 age-and gender-matched controls. The smoking status was evaluated by smoking index (SI). The CSM cases had a significantly higher prevalence of Trp2 alleles (Trp2+) than controls (19.8 vs 6.2%, P = 0.002), but the prevalence of Trp3 alleles (Trp3+) was similar between the two groups (23.3 vs 21.6%, P = 0.713). Logistic regression analyses showed that the subjects with Trp2+ had a higher risk for CSM. We thus analyzed whether smoking status influenced the association between Trp2 alleles and CSM risk. Among Trp2+ subjects with an SI less than 100, the smoking status did not influence the effect of risk for SCM [odds ratio (OR) = 1.34, 95% confidential interval (95%CI) = 0.85-2.18, P > 0.05]. When SI increased from 101 to 300, the OR for CSM reached 3.34 (95%CI = 2.11-5.67, P = 0.011); when SI was more than 300, the OR for CSM reached 5.56 (95%CI = 3.62-7.36, P < 0.001). Among Trp2-subjects with SI more than 300, the OR for CSM increased 2.14 (95%CI = 1.15-4.07, P = 0.024). We found a significant association between the Trp2 alleles and CSM risk and smoking amplifies this risk, suggesting that smoking abstinence is important for reducing CSM occurrence in subjects with high genetic risk.