IL1A and periodontitis: Table 1 exhibits data on age, sex, and n° cigarettes/day for each group. Table 2 displays the distribution of cases by periodontitis group and genotype. The genotype frequencies of the three studied SNPs were confirmed to be in Hardy–Weinberg equilibrium in the control group (p = 1.00 for IL-1A, p = 1.00 for IL-1B, p = 0.35 for IL-1RN).