Exploring the Causal Effect of Mitochondrial DNA Copy Number on Obstructive Sleep Apnea

Although some studies have established a clear association between mitochondrial DNA (mtDNA) copy number and obstructive sleep apnea (OSA), the causative relationship between the two remains unclear, which is what this study aims to explore.

We investigated the causal relationship between mtDNA copy number and OSA based on public genome-wide association study data utilizing a two-sample Mendelian randomization (MR) analysis and also explored the mediating role of immune cells between the two using a mediator MR analysis. We estimated the causal effects primarily using the inverse variance weighted method and conducted sensitivity analyses based on the MR-Egger intercept method and Cochran's Q test.

We found that mtDNA copy number had a significant negative causal effect on OSA (odd ratio [OR] [95% confidence interval (CI)] = 0.844 [0.778-0.911], p = 0.03), whereas OSA did not have a causal effect on mtDNA copy number (OR [95% CI] = 0.995 [0.979-1.01], p = 0.791). We identified that the terminally differentiated CD4-CD8^- T cell Absolute Count met the requirements for mediation analysis (OR [95% CI]_{as exposure} = 0.989 [0.985-0.993], p = 0.016, OR[95% CI]_{as outcome =} 0.717 [0.529-0.973], p = 0.033). Under this condition, the mediation effect size of the immune cell was 0.003, which is considered to have no mediating effect either using the bootstrap method or the two-step method (p > 0.05).

Our study indicates that reducing mtDNA copy numbers is a risk factor for the development of OSA, rather than a consequence of it. Improving mitochondrial dysfunction may help prevent or treat OSA.