[Mendelian randomization analysis: the causal relationship between the DNA methylation levels of JAK2 and obesity]

Objective: Based on the Mendelian randomization analysis, to assess the causal relationship between DNA methylation levels of Janus kinase 2 (JAK2) and obesity. Methods: A case-control study was carried out, including 1 021 individuals [obesity (visceral fat index ≥10) vs. no obesity (visceral fat index <10) was 440 vs. 581] from the Henan Rural Cohort Study. MethylTarget^TM target region methylation sequencing technology was used for testing the DNA methylation level of JAK2. logistic regression models were used to assess the association between the DNA methylation level of JAK2 and obesity. With SNP as the instrumental variable, the association between the DNA methylation level of JAK2 and obesity was explored by using the Mendelian randomization analysis method. Results: There was a positive association between Chr9:4984943 (one DNA methylation site in the promoter of JAK2) and obesity, and the OR (95%CI) was 1.22(1.04-1.42). Methylation level of five sites in the exon of JAK2 (Chr9:4985378, Chr9:4985404, Chr9:4985407, Chr9:4985409 and Chr9:4985435) were negatively associated with obesity, the corresponding OR (95%CI) were 0.53 (0.29-0.95), 0.58(0.36-0.93), 0.69 (0.49-0.97), 0.72 (0.53-0.99) and 0.58 (0.35-0.98) , respectively. Mendelian randomization analysis showed that there was a causal relationship between the DNA methylation levels of JAK2 and obesity, and the corresponding β (95%CI) were -1.985 (-3.520 - -0.450),-3.547 (-6.301 - -0.792) and -3.900 (-6.328 - -1.472) for Mendelian randomization method of inverse variance weighted, Mendelian randomization method of median based and Maximum-likelihood method, respectively. Conclusion: This study supported there was a causal relationship between the DNA methylation level of JAK2 and obesity.