Background: Periodontitis is a bacterial disease modified by multiple risk factors. The pro-inflammatory cytokine interleukin- (IL-1) is a key regulator of the host responses to microbial infection and a major modulator of extracellular matrix catabolism and bone resorption. It has been reported that variations in the IL-1 gene cluster on chromosome 2 are associated with increased susceptibility to severe adult periodontitis.
Methods: The present study evaluated the association between a composite IL-1 genotype, including allele 2 at each of two loci (IL-1A +4845 plus IL- B +3954), and a broad spectrum of periodontally healthy to diseased patients in a population that is typically encountered in a dental practice setting. Ninety patients, non-smokers or former smokers with less than 10 pack-year (pk/yr) history, were recruited from a private dental practice. The major outcome variable was bone loss determined by computerized linear measurements of radiographs. Genotypes were analyzed from finger-stick blood samples using previously reported methods.
Results: Multivariate logistic regression models demonstrated that patient age, former smoking history, and the IL-1 genotype were significantly associated with severity of adult periodontitis. For non-smokers or former light smokers (<5 pk/yr), IL-1 genotype positives were at increased odds ratio of having moderate to severe periodontal disease of 3.75 (95% CI: 1.04-13.50) to 5.27 (95% CI: 1.23-22.70), depending on ethnicity, compared to IL-1 genotype negatives. Former moderate smokers (>5 pk/yr and <10 pk/yr) who were IL-1 genotype negative were at increased odds ratio of having moderate to severe periodontal disease of 7.43 (95% CI: 1.20-46.20) compared to non-smokers or former light smokers who were IL-1 genotype negative. In addition, past smoking history was also a significant effect modifier as demonstrated by the statistically significant interaction between past smoking history status and IL-1 genotype status.
Conclusions: This study demonstrates that the composite IL-1 genotype is significantly associated with the severity of adult periodontitis. It also confirmed that both IL-1 genotyping and smoking history provide objective risk factors for periodontal disease in a private practice environment.