HLA antigens and linkage disequilibrium patterns in Turkish Behçet's patients.
Behçet's disease (BD) is a multisystem disorder featuring mucocutaneous, ocular, articular, vascular, intestinal, pulmonary, and neurologic involvement. Although the pathogenesis of the disease is still unknown, most studies have proposed that immunologic factors may play a major role in its development in genetically predisposed individuals. Seventy-one Turkish patients with BD, diagnosed according to the International Study Group for Behçet's Disease criteria, were studied and compared with 600 healthy controls to determine not only frequencies of HLA-A, B, and DR antigens but also whether BD shows any distinct linkage disequilibrium (LD) patterns. In addition, three-point linkage disequilibrium and relative risk (RR) values were determined. Of the HLA-A, B, and DR antigens examined, only B5 (51) was significantly increased in the patient group (X2 = 55.4; p < 0.05; RR = 6.44). DR7 was significantly decreased in the patient group (X2 = 6.9; p > 0.05; RR = 0.31). HLA haplotype B5-DR5 was found to be in negative LD in the control group, but Behçet's patients showed a strong positive LD between these two antigens. HLA haplotypes A2-B12, B5-DR2, and B12-DR4 showed negative LD in the patients; A1-B5 and B5-DR5 had positive LD in the patients. HLA haplotype A2-B5-DR5 was found to be more frequent than expected in both patients and control groups. A2-B12-DR4 showed a negative LD in the patients. The strong LD patterns between HLA-B and DR antigens in BD suggest that the susceptibility gene to BD could reside between the these two antigens.