Previous in vitro and in vivo experiments suggested the greater susceptibility in females is partly due to a protective effect of androgens.11 However, this protective role has not been confirmed through population-based studies, especially among women, due to the limited sample sizes and difficulties in accurately measuring fluctuating sex hormone levels.5,6,8,12 In our study, using unprecedentedly large samples, we could not detect any evidence of a causal association between naturally increased testosterone and MS development in women. This evidence concerns the gene PLXNA3 and myeloid sarcoma.