2. Genetic factors Y A high incidence among monozygotic twins(30% x50%), first-degree relative Y Role of hla-dr4 in the susceptibility to and severi of ra 70%Ra patients, a relative risk of having ra with hla DR4 of 4 to 5 The susceptibility epitope( shared epitope共同表位) QKRAA或 QRRAA It was considered to be related with the severity of established ra2. Genetic factors ✓ A high incidence among monozygotic twins (30% ~50%),first-degree relative ✓ Role of HLA-DR4 in the susceptibility to and severity of RA − 70% RA patients ，a relative risk of having RA with HLA￾DR4 of 4 to 5 − The susceptibility epitope (shared epitope 共同表位): QKRAA或QRRAA − It was considered to be related with the severity of established RA