Abstract 1674: Two phase study of KCNJ1 polymorphisms, calcium, magnesium and colorectal adenoma risk, results from the Tennessee Colorectal Polyp Study

Background: Previous studies generated inconsistent results on the associations between intakes of calcium and magnesium with risk of colorectal adenoma and cancer. It is possible that some of the inconsistency is due to a modifying effect by genetic polymorphisms involved in calcium and magnesium homeostasis. The KCNJ1 gene encodes the Inward-rectifier potassium channel (ROMK). ROMK plays an essential role in the homeostasis of potassium, which is critical for the reabsorption of calcium and magnesium. Objectives: We hypothesize that common variants in KCNJ1 may modify the associations between intakes of calcium and/or magnesium and risk of colorectal adenoma risk. Methods: Included were participants of the Tennessee Colorectal Polyp Study (TCPS), a colonoscopy-based case control study conducted in Nashville, TN. In the phase I study, genotyping was performed using the Affymetrix Human Mapping 500K array set in 958 colorectal adenoma cases and 909 controls and 13 tagging single-nucleotide polymorphisms (SNPs) in the KCNJ1 gene were evaluated. SNPs identified as significant in phase I were genotyped in phase II in an independent set (860 cases and 3083 controls). Results: In phase I, 1 tagging SNP was significantly associated with adenoma risk and 8 SNPs were interacted significantly with calcium or magnesium intake in risk of colorectal adenoma. In phase II, only 1 of the 9 SNPs significantly interacted with calcium and magnesium intakes in relation to colorectal adenoma although the genotype per se was not directly associated with the risk. In combined analysis, the p value for the interaction between the SNP and calcium intake was 0.00015 and it remained statistically significant after Bonferroni correction for multiple comparisons. In stratified analyses by levels of calcium and magnesium (above or below RDA levels), we found adenoma risk significantly increased for those who with at least 1 variant allele and whose intake levels of calcium and magnesium were below the RDA levels, with ORs (95% CI) of 1.35 (1.10, 1.67) and 1.43 (1.08, 1.89) respectively, compared to those who did not possess the variant allele. The corresponding ORs (95% CI) increased to 1.84 (1.33, 2.53) and 2.30 (1.53, 3.46), respectively, multiple adenomas versus controls. Conclusions: In this two-stage analysis, we found no overall association of adenoma with KCNJ1 genotype. However, common KCNJ1 variants significantly interacted with intakes of calcium and magnesium in risk of colorectal adenoma, particular for multiple adenomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1674. doi:1538-7445.AM2012-1674