IL1A and periodontitis: Kornman et al. (1997) showed for the first time that the combined presence of allele 2 (allele with nucleotide sequence changed) of the IL-1A gene at nucleotide position –889 (IL-1A-889T) and the allele 2 of IL-1B gene at nucleotide position + 3954 (IL-1B+3954T) was associated with an increased risk for developing severe periodontitis in nonsmoking Caucasian patients.