Distribution of Polymorphic Genotypes in Indigenous and Non-Indigenous Mexican Populations

Objectives: To determine and compare the distribution of 10 polymorphisms of genes encoding for inflammatory cytokines in 3 indigenous Mexican populations (Otomi, Mazahua & Huichol Indians) and non-indigenous (mestizo) Mexican subjects with generalized chronic-periodontitis (GCP), generalized aggressive-periodontitis (GAgP) and periodontal-health (PH). Methods: 84 indigenous subjects (Otomi Indians n=42, Mazahua Indians n=27, Huichol Indians n=15) and 126 non-indigenous subjects (GCP n=60, GAgP n=26, PH n=40) were selected for the study. Clinical measurements including plaque accumulation, gingival erythema, bleeding on probing, suppuration, pocket depth and attachment level were recorded (6 sites per tooth). Genotypes of polymorphisms IL-1A(-889), IL-1B(+3954), IL-1B(-511), IL-1RN(int2), TNF-B(+252), IL-8(-251), IL-10(-592), IL-10(-819), IL-10(-1082) & IL-12(+1188) were determined by RFLP. The associations between genotype frequencies for each polymorphism were determined among groups using Fisher's exact test. Risk estimates were calculated by Mantel-Haenszel's common odds-ratio (OR) with 95% confidence intervals (CI). Results: Significantly elevated frequencies of genotypes IL-1B(+3954)A2/A2, TNF-B(+252)A2/A2 & IL-8(-251)A1/A1 characterized non-indigenous subjects and distinguished them from the indigenous populations (p<0.001, OR=15.9, CI=3.7-67.7; p<0.001, OR=3.1, CI=1.7-5.4 & p<0.001, OR=10.7, CI=3.7-30.9, respectively). Otomi Indians were genetically distinct from the rest of the populations exhibiting a lower frequency (10.7% vs. 33.4% to 46.6%) of IL-1A(-889)A2 (p<0.05, OR=7.3, CI=1.5-35.1) and were the only group in which carriers of IL-1RN(int2)A4 were detected. The composite genotype previously described as a marker for predicting susceptibility to periodontal disease (IL-1B(+3954)A2 & IL-1A(-889)A2) did not associate with either GCP or GAgP in Mexican subjects. However, the composite genotype IL-1B(-511)A2/A2 & IL-1A(-889)A1/A1 significantly associated with GAgP in non-indigenous Mexican subjects (p<0.01, OR=6.0, CI=1.7-20.2). Conclusions: Our findings reveal that specific polymorphic genotypes patterns may characterize defined populations even within relatively restricted geographical areas. Furthermore, they suggest that polymorphisms described as markers for periodontal disease might only be useful for the populations in which the associations were established. Supported by DGAPA-PAPIIT IN213006-3.