Variants of the PPARG, IGF2BP2, CDKAL1, HHEX, and TCF7L2 genes confer risk of type 2 diabetes independently of BMI in the German KORA studies.

Genome-wide association (GWA) studies identified novel gene variants that are associated with type 2 diabetes. However, results were not always consistent across different populations. Thus, the aims of this study were (i) to replicate findings from previous GWA studies in mainly Northern European populations using data from the German KORA 500 K diabetes project and (ii) to assess the impact of BMI on associations between single nucleotide polymorphisms (SNPs) and type 2 diabetes. The KORA 500 K diabetes project includes 433 cases with validated type 2 diabetes and 1 438 nondiabetic controls from two population-based KORA surveys. Genotyping was performed using the Affymetrix GeneChip Human Mapping 500 K Array Set. We investigated associations between SNPs and type 2 diabetes in 10 genes that have been reported to increase the risk of type 2 diabetes or were in complete or near-complete linkage disequilibrium with these variants. SNPs in the CDKAL1 gene showed the strongest association with type 2 diabetes [range of age and sex-adjusted odds ratios (OR): 1.30-1.39, p-values 0.0008-0.0004]. In addition, we found evidence for association of SNPs in the genes PPARG, IGF2BP2, HHEX, TCF7L2, and FTO with type 2 diabetes in the same directions as previously described (p<0.05), but not for WFS1, CDKN2A/B, KCNJ11, or EXT2. Adjustment for BMI slightly strengthened the link between CDKAL1 and type 2 diabetes, but had almost no impact on the other associations. We conclude that gene variants of CDKAL1, PPARG, IGF2BP2, HHEX, TCF7L2, and FTO predispose to type 2 diabetes in the German KORA 500 K study population. These associations appear to be independent of BMI.