Do Alopecia Areata and Hair Colour Have a Shared Genetic Component?

Alopecia areata (AA) is a common T-cell mediated autoimmune disorder, which leads to sudden, non-scarring hair loss. An association between hair pigmentation and AA pathogenesis has long been postulated. Recent epidemiological evidence supports this link, indicating that individuals with darker hair colours have a higher risk of AA, while those with lighter hair colours exhibit a lower risk. This study aimed to investigate whether a shared genetic basis between hair colour determination and AA risk underlies this observation. To explore this, we analysed data from our AA genome-wide association study (GWAS) of 16 310 Caucasians from the US and Central Europe and a recently published GWAS of hair colour that involved 343 234 UK Biobank participants. Genetic correlations between the two traits were investigated using both polygenic risk score and linkage disequilibrium score regression (LDSC) analyses. No evidence was found for a strong, broadly shared genetic component for hair colour and AA. However, a suggestive weak inverse association with genetically predicted blond hair and AA risk was observed. Given the modest sample size of the AA-GWAS (~4100 cases), these findings are likely underpowered and should be interpreted as exploratory and hypothesis-generating, warranting replication in larger, independent cohorts.