HLA-DRB1 and mixed connective tissue disease: The susceptibility alleles for MCTD were similar to those for rheumatoid arthritis (HLA-DRB1*01:01, DRB1*04:01, DRB1*04:05, DRB1*04:10, DRB1*09:01, DRB1*10:01)27, except that DRB1*04:05 is the most important risk allele for Japanese rheumatoid arthritis, which was not shared with MCTD.