Organ Specificity in Autoimmune Diseases: Thyroid and Islet Autoimmunity in Alopecia Areata

Context: Multiple autoimmune diseases, such as autoimmunity against the thyroid gland and pancreatic islets, are often observed in a single patient. Although alopecia areata (AA) is one of the most frequent organ-specific autoimmune diseases, the association of AA with other autoimmune diseases and the genetic basis of the association remain to be analyzed. Objective: The aim of this study was to clarify the similarities and differences in HLA and clinical characteristics of thyroid and islet autoimmunity in patients with AA. Participants: A total of 126 patients with AA were newly recruited. Anti-islet and antithyroid autoantibodies were tested, and genotypes of HLA genes were determined. Results: Among the autoimmune diseases associated with AA, autoimmune thyroid disease was most frequent (10.0%), followed by vitiligo (2.7%) and rheumatoid arthritis (0.9%) but not type 1 diabetes (0.0%). The prevalence of thyroid-related autoantibodies in patients with AA was significantly higher than that in controls (TSH receptor antibody [TRAb]: 42.7% vs 1.2%, P = 1.6 x 10(-46); thyroid peroxidase antibody: 29.1% vs 11.6%; P = 1.7 x 10(-6)), whereas the prevalence of islet-related autoantibodies was comparable between patients with AA and control subjects. The frequency of DRB1*15:01-DQB1*06:02, a protective haplotype for type 1 diabetes, was significantly higher in TRAb-positive (12.8%, P = .0028, corrected P value [P-c] = .02) but not TRAb-negative (7.1%, not significant) patients with AA than in control subjects (4.5%). The frequency of DRB1*04:05-DQB1*04: 01, a susceptible haplotype for type 1 diabetes, was significantly lower in patients with AA (TRAb-positive: 8.5%; TRAb-negative: 11.9%) than in those with type 1 diabetes (29.5%, P-c = .0003 and P-c = .0008, respectively). Conclusion: AA was associated with thyroid autoimmunity but not islet autoimmunity, which correlated with class II HLA haplotypes susceptible or resistant to each autoimmune disease.