Epidemiologic and genetic characteristics of alopecia areata (part 2)

Alopecia areata (AA) is hypothesized to be an organ-specific autoimmune disease mediated by T cells to the hair follicles. Despite the fact that most cases of AA are sporadic, there is an accumulation of evidence that AA is a complex multigenetic trait with components of inherited predisposition. In the last decade, rapid progress in molecular genetics and biotechnology has led to the identification of many candidate genes in humans that confer susceptibility to AA. The first part of this review focused on the association of HLA genes with the disease. The second part reviews non-HLA and other genes associated with AA, including the autoimmune regulator (AIRE) gene. Recently, the lymphoid-specific protein tyrosine phosphatase, non-receptor type 22 (PTPN22) gene was found to be an additional immunoregulatory gene associated with AA. In addition, alleles of genes coding for cytokines and their receptors, such as the interleukin-1 receptor antagonist (IL1RN) and chemokines (MCP-1), have also been associated with AA. Some studies have hypothesized that filaggrin gene mutations (FLG) may also play a role in AA, particularly in patients with comorbid atopic disease. MX1 is another new candidate gene in AA. Thus, this second part of the review completes the overview of current knowledge about the molecular genetics of AA begun in the first part.