Previous epidemiological studies have indicated a role for telomere length in multiple sclerosis (MS) severity and phenotype. However, these studies failed to establish the causality between telomere length and MS susceptibility. Hence, we performed two-sample Mendelian randomization (MR) analysis to explore the causal relationship between telomere length and MS susceptibility.
We used data of genetic variants associated with leukocyte telomere length as instrumental variables (IVs), which was identified from the largest and latest genome-wide association study (GWAS) from UK Biobank (UKB) with 472,174 participants. Summary data of MS was obtained from the International Multiple Sclerosis Genetics Consortium. We performed two-sample MR analyses using the inverse-variance weighted method as the primary approach. Other MR approaches, including the MR-Egger, the inverse variance weighted (multiplicative random effects), weighted median, simple median, weighted mode-based methods, and Causal Analysis Using Summary Effect estimates (CAUSE), were also conducted to detect the result robustness.
The genetic liability to longer telomere length was associated with a higher risk of MS susceptibility (odds ratio [OR] per one-SD telomere length, 1.91; 95% confidence interval [CI], 1.48-2.47; P = 8.04 × 10). The results remained consistent across multiple sensitivity analyses.
Our study supports the causal relationship between longer telomere length and increased risk of MS susceptibility.

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