Susceptibility of major groups of Tamil Nadu to diseases: 1. Psoriasis vulgaris

Eighty-three patients with psoriasis vulgaris, living in Madurai, Tamil Nadu, India, were studied for HLA-A, HLA-B, HLA-C, HLA-DR and HLA-DQ antigen frequencies and compared with seventy-seven controls studied using the same batch of reagents. A highly significant increase of frequency of HLA-Bw57, a split of HLA-B 17, was found in the patients; Bw58, another split of B17, was absent. Relative risk was high for A1, B17, Bw57 and DR7 individuals; it was highest for Bw57. Frequencies of the haplotypesAl-Bw57 andDR7-DQw3 were also significantly higher in patients. Analysis of the HLA data based on ethnic differences identified as major groups revealed high relative risk for B17, Bw57 and DR7 only in major group III, a Western brachycephal Armenoid group, but not in major group II, a Mediterranean one thought to be an earlier settler of this region. Analysis of the data based on age and sex subgroups yielded interesting information. The age at onset of the disease in the total patient sample showed a bimodal distribution. The two sexes differed in their age-at-onset distributions: females showed a preponderance of early onset of the disease (< 30 years of age, 68%), while the majority of males had late onset (>30 years of age, 71%). HLA data for the early-onset patients indicate very high relative risk for B17, Bw57 and DR7. This suggests that psoriasis may be influenced by sex, and that the early-onset and late-onset forms of the disease may be of different aetiopathogenesis. These observations stress the importance of considering the ethnic origin or composition of samples, and age, sex and other parameters in HLA and disease association studies.