Exploring the Impact of 731 Immunophenotypes on Alopecia Areata Risk: A Mendelian Randomization Analysis With Plasma Metabolites as Mediators.

OBJECTIVE

This study aimed to delineate the causal relationship between immunophenotypes and alopecia areata (AA) and to assess the intermediary role of plasma metabolites.

METHODS

The authors utilized bidirectional Mendelian randomization (MR) to parse the causal associations between 731 immunophenotypes and AA using genome-wide association study (GWAS) summary statistics from 767 cases and 394,105 controls. A 2-step MR strategy was adopted to quantify the influence of 1400 plasma metabolites on AA through their impacts on immunophenotypes.

RESULTS

The MR findings indicated that an elevated genetically predicted expression of HLA DR on CD14+ CD16- monocytes correlates with an augmented AA risk [Odds Ratio (OR) = 1.199, 95% CI = 1.079-1.332, P = 0.0007]. This association was primarily estimated using the inverse variance weighted (IVW) method. In contrast, the data did not provide robust evidence supporting an influence of genetically predicted AA on the expression of HLA DR in these monocytes (OR = 1.008, 95% CI = 0.989-1.028, P = 0.401). The mediating effect of glycochenodeoxycholate glucuronide on the immunophenotype-AA relationship was quantified at 6.5%, whereas arachidoylcarnitine (C20) mediated 4.7% of the effect.

CONCLUSION

The analysis substantiates a causal link between HLA DR expression on CD14+ CD16- monocytes and AA, with partial mediation by arachidoylcarnitine (C20) and glycochenodeoxycholate glucuronide. The principal mechanisms by which HLA DR affects AA are yet to be fully elucidated, necessitating further investigations to uncover additional mediators and risk factors.