Background: Psoriasis vulgaris was reported to be associated with a specific alanine residue at position 73 of HLA-C alleles in Japanese patients. Objective: Our purpose was to determine the role of HLA genes in susceptibility to psoriasis vulgaris in the Israeli Jewish population. Methods: Twenty-eight Israeli patients were analyzed for their HLA class I and II specificities by means of serologic and molecular methods. Results: All patients possessed in their HLA-C antigens an alanine residue at position 73 (p < 0.002). A significantly increased frequency of HLA-Cw6 and of Cw7 was also observed among the patients (p < 0.02). Conclusion: Our study clearly shows that alanine in position 73 is significantly associated with psoriasis vulgaris in Jewish patients. Cw6 and Cw7 have a unique antigen-binding pocket containing both alanine at position 73 and a negatively charged aspartic acid at position 9. These residues are most probably important in determining the conformation of the C pocket and in turn the nature of the peptide bound to it. We suggest that this combination confers the highest risk of the development of psoriasis vulgaris.
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