The HLA class II region encodes the strongest genetic contribution to insulin-dependent
diabetes mellitus (IDDM); however, the complex HLA associations with IDDM are not yet
fully understood. Here, Jin-Xiong She argues that all DR and DQ molecules in an individual
act in concert to determine the overall HLA-encoded susceptibility to IDDM and that
apparent inter-racial discrepancies of HLA associations can be explained by DR-DQ linkage
disequilibrium or by DQ αβ trans-complementation.