# Causal relationship between asthma and ankylosing spondylitis: A bidirectional two-sample univariable and multivariable Mendelian randomization study

## TL;DR

This study finds a causal link between asthma, especially eosinophilic asthma, and an increased risk of ankylosing spondylitis.

## Contribution

The study identifies a direct causal effect of asthma on ankylosing spondylitis using Mendelian randomization.

## Key findings

- Eosinophilic asthma is associated with a 24% higher risk of ankylosing spondylitis.
- Adjustments for BMI, smoking, and alcohol confirmed a direct causal effect of asthma on AS.
- Allergic and childhood-onset asthma showed no causal link to ankylosing spondylitis.

## Abstract

Previous research has indicated a possible association between asthma and ankylosing spondylitis (AS).

We pinpointed single nucleotide polymorphisms linked to various forms of asthma and AS, employing them as instrumental variables for a bidirectional two-sample Mendelian randomization (TSMR) analysis. Our TSMR analysis focused on European populations to minimize racial confounding. Multivariate adjustments for body mass index (BMI), smoking, and alcohol use were performed to control for confounders. Colocalization analysis was used to validate MR findings and explore genetic links between asthma and AS.

Individuals with asthma and eosinophilic asthma exhibited a relatively higher risk of AS (asthma: OR 1.31, 95% CI 1.07–1.62, P = 0.008; eosinophilic asthma: OR 1.24, 95% CI 1.005–1.544, P = 0.044). Allergic asthma, childhood-onset asthma, and obesity-related asthma showed no causal relationship with AS (allergic asthma: IVW P = 0.27; childhood-onset asthma: IVW P = 0.66; obesity-related asthma: IVW P = 0.53). After adjusting for cigarette smoking, alcohol consumption, and BMI, the results supported a direct causal effect of asthma on the increased risk of AS onset (IVW P = 0.001).

This study revealed that a positive causal connection between asthma, specifically eosinophilic asthma, and AS.