[Contribution of genetic factors to RA]

Multiplex families of rheumatoid arthritis (RA) and concordance of the development of RA in monozygotic twins strongly suggest the relationship of genetic factor to the onset of RA. Among many genetic markers, HLA shows the strongest association with RA and association between RA and HLA-DR4 has been reported in many ethnic groups. DNA typing of HLA class II genes revealed that DRB1 * 0405 (Dw 15) is the most susceptible DRB1 allele for RA in the Japanese. The particular epitope sequence at the third hypervariable region (position 70-74, and 86) and DR beta chain, expressed with the structure of the DR4 molecule seems to be important for the susceptibility to RA.