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The causal relationship between body mass index and perianal abscess: a Mendelian randomization study
Long Wu1, Huan Wu2, Xiao-Yun Li1
1Department of Colorectal Cancer Center, The Affiliated Hospital of Guizhou Medical University, Guiyang, Guizhou Province, 550001, China.
Background:
Observational studies suggest an association between elevated body mass index (BMI) and perianal abscess risk, but residual confounding and reverse causality limit causal inference. Mendelian randomization (MR) offers a robust approach to assess causality by leveraging genetic variants as instrumental variables. This study aimed to evaluate the causal relationship between BMI and perianal abscess using a MR framework.
Methods:
We analyzed European-ancestry genome-wide association study (GWAS) data for BMI (n = 359,983) and perianal abscess (1,287 cases/182,423 controls). A total of 364 independent SNPs associated with BMI at genome-wide significance (P < 5 × 10⁻⁸) were selected as instrumental variables, with stringent linkage disequilibrium clumping (r² < 0.01, clumping distance > 10,000 kb). Causal estimates were derived using inverse-variance weighted (IVW), MR-Egger, weighted median, and MR-PRESSO methods. Multivariable MR (MVMR) adjusted for lipid metabolism disorders and insulin resistance. Sensitivity analyses assessed pleiotropy, heterogeneity, and instrument strength.
Results:
Genetically predicted higher BMI was causally associated with an increased risk of perianal abscess (IVW: OR = 1.94, 95%CI: 1.46-2.68, P = 3.8 × 10⁻⁶). Consistency across methods (MR-Egger: OR = 2.80; weighted median: OR = 2.30) and MVMR adjustment (OR = 1.47, 95%CI: 1.12-1.93) supported robustness. No evidence of directional pleiotropy (MR-Egger intercept P = 0.30) or heterogeneity (I² = 7.6%; MR-PRESSO global test P = 0.148) was observed. Instrument strength was sufficient (mean F-statistic = 37.75), mitigating weak instrument bias.
Conclusion:
This MR study provides robust genetic evidence supporting BMI as a causal risk factor for perianal abscess. The findings highlight obesity management as a potential preventive strategy, though multifactorial mechanisms warrant further investigation.
Insights
Elevated body mass index (BMI) causally increases perianal abscess risk. This genetic study suggests obesity management may be a key preventive strategy for perianal abscess.
Area of Science:
- Genetics and Epidemiology
- Public Health
Background:
- Observational studies indicate a link between higher body mass index (BMI) and perianal abscess risk.
- Limitations of observational studies include confounding and reverse causality, necessitating robust causal inference methods.
Purpose of the Study:
- To investigate the causal relationship between BMI and perianal abscess risk.
- To utilize Mendelian randomization (MR) to overcome limitations of observational studies.
Main Methods:
- Employed a two-sample MR design using genome-wide association study (GWAS) data for BMI and perianal abscess in a European-ancestry population.
- Selected 364 independent single nucleotide polymorphisms (SNPs) for BMI as instrumental variables, applying stringent quality control.
- Utilized inverse-variance weighted (IVW), MR-Egger, and weighted median methods for causal effect estimation, with MR-PRESSO for pleiotropy assessment. Multivariable MR (MVMR) adjusted for potential confounders.
Main Results:
- Genetically predicted higher BMI demonstrated a significant causal association with increased perianal abscess risk (IVW OR=1.94, P=3.8×10⁻⁶).
- Results were consistent across multiple MR methods and robust after MVMR adjustment for lipid and insulin resistance pathways.
- Sensitivity analyses confirmed no significant directional pleiotropy or heterogeneity, and adequate instrument strength.
Conclusions:
- This MR study provides strong genetic evidence that elevated BMI is a causal risk factor for perianal abscess.
- Findings support obesity management as a potential preventive measure for perianal abscess.
- Further research is warranted to explore the multifactorial mechanisms underlying this association.
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