DNA polymorphism of HLA class II genes in alopecia areata.

We investigated the DNA restriction polymorphism (RFLP) of the Major Histocompatibility Complex (MHC) class II genes: HLA-DQA, -DQB, -DPA, and -DPB in 20 Danish patients with alopecia areata (AA) and in healthy Danes. The frequency in AA of the DQB1*0301 and DQw7 associated DQB Bgl/II 4.2 kb fragment was increased to 65.0 per cent compared to 23.2 per cent in controls (RR = 6.1; p less than 10(-3)) suggesting that the previously reported associations between AA and both DR4 and DR5 is secondary to an association between AA and DQB1*0301, which codes for the beta-chain of the HLA-DQ molecule of the serologically defined HLA-DQw7 specificity. Individuals who carried both DQA1*0501 and DQB1*0301 seemed to have a further increased risk of developing AA compared to individuals carrying only one of these HLA class II genes. Analysis of the combined presence of DQB1*0301 and DPA1*0103 in AA suggests that an additive risk effect (synergism or interaction) exists between the DQB1*0301 and DPA1*0103 alleles which are situated at different HLA class II loci.