Organ specificity in autoimmune diseases: thyroid and islet autoimmunity in alopecia areata

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.

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.

A total of 126 patients with AA were newly recruited. Anti-islet and antithyroid autoantibodies were tested, and genotypes of HLA genes were determined.

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 × 10(-46); thyroid peroxidase antibody: 29.1% vs 11.6%; P = 1.7 × 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 [Pc] = .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%, Pc < .0003 and Pc < .0008, respectively).

AA was associated with thyroid autoimmunity but not islet autoimmunity, which correlated with class II HLA haplotypes susceptible or resistant to each autoimmune disease.