[A search for genes of predisposition to rheumatoid arthritis]

Rheumatoid arthritis belongs to the group of autoimmune multifactor diseases with an essential involvement of genetic components in its genesis. The HLA DRB1* polymorphism was studied in 68 RA patients and in their 75 healthy relatives. 135 blood donors, who were tested at the Institute for Immunology of the Ministry of Health, Russian Federation, Moscow, were in the control group. The carrier-state of the HLA DRB1* 04 gene contributes to a higher probability of RA onset by 8.5 times, while the presence, in genotype, of genes HLADRB1* 02, 05, 06 reduces the risk of RA by 2.1, 2.3 and 7.2 times, respectively. Allele *0401 is encountered reliably more often in RA patients versus healthy controls. Within a sample of patients with familial RA, 43.9% turned out to be the carriers with various combinations of two alleles of genes coding the conservative amine acids of sequences QKRAA or QRRAA, which were named "shared epitope" (SE), versus 5.1% among the controls. The presence of homozygous "SE genotypes" among the RA patients contributed to a higher risk of morbidity by 5.8 times, while the carrier state of haplotypes with "duel SE positivity" enhanced the risk of morbidity by 17.8 times mainly due to the 01/0401 halotype. The RA linkage with two intragenic DNA markers, i.e. with the polymorphous micro-satellite replication of gene TCRA (CA)n and with the point-type changeability (localized in the coding area of the second variable region of V2 TCRD gene), was analyzed. The maximal possible value of the lod-point for (CA)n, i.e. replication of TCRA gene, was equal to +1.30 in males under the condition of zero recombination frequency, and to 16% of frequency recombination in females. The maximal possible value of the lod-point for the point-type changeability of gene TCRD was equal to +0.70 in males under the conditions of zero frequency recombination and to 40% of frequency recombination in females. The maximal lod-point value amounting to +1.20 in males and females in an identical frequency recombination of 5% was found on the basis of a three-point analysis of the linkage between RA and two intragenic markers from gene clusters coding the alpha- and beta-chains of T-cellular receptors. Therefore, our familial data are indicative of the opportunity of localizing the gene predisposed to RA is at a distance of 5 cM, in the direction of the telomere, from the locus of the examined (CA)n, i.e. replication of gene TCRA.