Genome-wide association studies (GWAS) in alopecia revealed single-nucleotide polymorphisms (SNPs) in regions encoding Treg signature genes such as CD25, the ikaros family member Eos (IKZF4), cytotoxic T-lymphocyte antigen 4 (CTLA-4) and Foxp3 (117, 119). This evidence concerns the gene CTLA4 and alopecia.