Low prevalence of a periodontitis-associated interleukin-1 composite genotype in individuals of Chinese heritage

Background: Polymorphisms in the interleukin-1 (IL-1) gene cluster have bee n associated with an increased risk of developing certain diseases. A speci fic composite genotype of IL-IA and IL-IB polymorphisms, consisting of alle le 2 of both IL-1A +4845 and IL-IB +3954 (formerly +3953) has been associat ed with an increased risk of Severe adult periodontitis. Approximately 30% of the European population carry this genotype. The prevalence of the above IL-1A and IL-1B composite genotype in populations of different ethnic orig ins is unknown. Therefore, the primary aim of this study was to determine t he prevalence of the IL-1 composite genotype in individuals of Chinese heri tage, since epidemiologic studies indicate that periodontitis is widespread among ethnic Chinese. An additional aim was to evaluate if there was an as sociation between the composite genotype and the severity of periodontal di sease. Methods: A convenience sample of 300 volunteers of Chinese heritage (ages 2 1 to 69 years) received a periodontal examination including full-mouth clin ical attachment loss measurements, probing depths, plaque index scores, and bleeding on probing. Blood was collected from a fingerstick and placed on a blotting paper card. The blood samples were analyzed for IL-1A +4845 and IL-IB +3954 polymorphisms using polymerase chain reaction (PCR)based method s. Results: Only 7 of the 300 subjects (2.3%) carried the composite IL-1 genot ype consisting of allele 2 of both IL-1A +4845 and IL-1B +3954. Allele 2 of the IL-1A +4845 polymorphism was carried by 17.0% (51/300) of the subjects ; of these, only 2 were homozygous. Allele 2 of the IL-1B +3954 polymorphis m was much rarer with only 3.3% (10/300) of the study population carrying t his marker. All of the people who carried the IL-1B polymorphism were heter ozygous. Too few of the subjects were positive for the IL-1 composite genot ype to establish any relationship with the susceptibility to periodontitis. Conclusions: It was concluded that the prevalences of both IL-1A and IL-1B polymorphisms are dramatically lower in Chinese than those reported for Eur opeans. Findings from this study bring into question the usefulness of the composite genotype of allele 2 of both IL-1A +4845 and IL-1B +3954 as a met hod for determining the susceptibility of Chinese patients to adult periodo ntitis.