Objectives: To evaluate the contribution of HLA class II region and the CTLA-4 gene in genetic susceptibility to rheumatoid arthritis (RA) and Sjögren's syndrome (SS) in the Tunisian population.
Methods: The polymorphisms of a (CA)n microsatellite of HLA-DQB1 CAR1/CAR2, TNFa IR2/IR4 and an (AT)n microsatellite in the 3'-untranslated region of exon 3 of the CTLA-4 gene were analysed after specific polymerase chain reaction (PCR) amplification. Typing of CTLA-4 A/G exon 1 polymorphism was achieved by the PCR-restriction fragment length polymorphism method.
Results: Genomic DNA from 60 patients with RA, 58 patients with SS and 150 healthy individuals was genotyped. The distribution of HLA-DQ CAR1/CAR2 allele frequencies differed between patients and controls in both diseases (RA, P<10(-15); SS, P=7.6x10(-15); RA+SS, P<10(-15)). The analysis of TNFa IR2/IR4 and CTLA-4 A/G polymorphisms did not show any differences in allele or genotype frequencies between patients and control subjects in either disease. The distribution of CTLA-4 (AT)n allele frequencies differed between patients with RA and controls (P=10(-3)), whereas no significant difference was detected between patients with SS and controls.
Conclusion: These data suggest the involvement of HLA-DQ CAR1/CAR2 polymorphisms in genetic susceptibility to RA and SS and the participation of the CTLA-4 gene, or a gene closely associated with it, in the development of RA.