Causal association between body mass index and risk of perianal abscess: A Mendelian randomization study

Abstract Background Perianal abscess is a common infectious disease affecting the perianal region. Body mass index (BMI) is a widely used indicator for assessing weight and obesity. Although obesity is known to be associated with multiple health issues, the understanding of the relationship between BMI and perianal abscess is limited. Whether BMI influences the risk of perianal abscess remains a subject of debate. Method A two-sample Mendelian randomization (MR) analysis using the inverse-variance weighted (IVW), weighted median, weighted mode and MR-Egger regression methods was performed. We used the publicly available summary statistics data sets of genome-wide association studies (GWAS) meta-analyses for BMI in individuals of South Asian (n = 8,658) as the exposure and a GWAS for abscess of anal and rectal regions from the individuals included in OpenGWAS database (total n = 183 710; case = 1 287, control = 182 423) as the outcome. Results We selected 29 single nucleotide polymorphisms (SNPs) at genome-wide significance from GWASs on BMI as the instrumental variables. The IVW method showed there is no evidence to support a causal association between BMI and perianal abscess (Beta = -0.093, SE = 0.097, P = 0.340). MR-Egger regression revealed that directional pleiotropy was unlikely to be biasing the result (intercept = 0.024; P = 0.285), and it also showed no causal association between BMI and perianal abscess (Beta = -0.254, SE = 0.177, P = 0.162). Moreover, the weighted median and weighted mode also approach no evidence of a causal association between BMI and perianal abscess (weighted median: Beta =- 0.126, SE = 0.139, P = 0.363; weighted mode: Beta = -0.207, SE = 0.182, P = 0.813). Cochran's Q test and the funnel plot indicated no evidence of heterogeneity and asymmetry, indicating no directional pleiotropy. Conclusion The results of MR analysis did not yield sufficient evidence to suggest a causal association between BMI and an elevated risk of perianal abscess.