Genetic background of obesity: a case-control study

The rising prevalence of obesity and type 2 diabetes mellitus (T2DM) constitutes a major global public health concern. Increasing evidence indicates that genetic polymorphisms may modulate the risk of T2DM in individuals with obesity, providing valuable insight into the biological pathways that connect these interrelated disorders. A better understanding of the genetic determinants underlying obesity-associated T2DM could enhance disease characterization and inform risk stratification strategies. The genetic architecture linking obesity and T2DM has, however, not yet been fully elucidated.

In this case-control study, we investigated the distribution of the TCF7L2 rs7903146, FTO rs9939609, and PPARG rs1801282 polymorphisms in 257 Greek adults with obesity (BMI > 30 kg/m²), including 136 individuals without T2DM and 121 with T2DM. The primary prespecified analysis applied unadjusted additive logistic regression to estimate per-allele odds ratios (ORs) for T2DM risk, while dominant and recessive inheritance models were evaluated as secondary analyses. Hardy-Weinberg equilibrium was assessed in the control group using an exact test. In participants without diabetes, genotype distributions were further compared across clinically defined HbA1c categories based on American Diabetes Association thresholds. The study was conducted and reported in accordance with STREGA guidelines.

Genotype distributions differed significantly between cases and controls for all three loci. In the additive model, each additional T allele at TCF7L2 rs7903146 was associated with higher odds of T2DM (OR 2.66, 95% CI 1.92-3.68; p < 0.001). Similar associations were observed for FTO rs9939609 (OR 1.52, 95% CI 1.14-2.03; p = 0.005) and PPARG rs1801282 (OR 1.98, 95% CI 1.41-2.77; p < 0.001). No statistically significant association was detected between the examined variants and HbA1c category in the non-diabetic group. In controls, all three loci deviated from HWE, with marked heterozygote deficits for TCF7L2 and FTO.

TCF7L2 rs7903146 and FTO rs9939609 were associated with T2DM among individuals with obesity in this cohort, whereas PPARG rs1801282 showed an association in the opposite direction from that reported in much of the prior literature. These findings should be interpreted cautiously because the regression models were unadjusted, while the control-group HWE deviations raise concerns regarding assay or sampling validity. Larger, well-characterized studies with participant-level covariate data and expanded quality-control procedures are required.