[Genetic determination of rheumatoid arthritis. Distribution of certain Mendelian markers in the light of correspondence of the disease heritability to the model of single autosomal two-allele locus with incomplete penetrance].

The study on the nature of distribution of certain mendelian markers aimed at specifying their role in determination of rheumatoid arthritis disease was carried out, based on the material from the Family Data Bank of the Department of Epidemiology and Genetics of the rheumatic diseases in this institute comprising data on 200 families of patients with definite rheumatoid arthritis (RA). Antigens of HLA-system (the loci A, B, DR), ABO blood groups, Rh, MN and P, phenotypes of acid erythrocyte phosphatase and the types of haptoglobin were studied. Based on the data from this and the previous studies, it is established that the steadiest deviations of the RA patients groups from the general population concerned the frequency of HLA A11, B12, B27 and DR4, blood group P and phenotypes of the acid erythrocyte phosphatase. When using additional controls--a group of healthy mothers of women-probands from the families with the type of marriage "healthy x healthy", and analysing some pair combinations of the HLA system antigens, it was demonstrated that the most clearly their role in formation of the disease display the antigens DR4, and in their absence--DR3, and B12, whereas accumulation of A11 and B27 depended on the presence of other antigens of HLA loci--A and B. Taken together, these data may imply that genetic markers under study serve, when in certain combinations, as "modifiers" of the major gene, or, in a general case, of major genes of multifactorial disease affecting its appearance and clinical manifestations.