As X alleles have been shown to be undertransmitted in the RA cohort (that is, noncarriers of risk alleles) (see Table 4), they were used as the control group within the RA cohort to determine the possible associations of the HLA-DRB1 genotype with RA-associated autoantibodies by comparing the total positive and negative results for the RA-associated antibodies (RF and aCCP) in the risk groups with those for the control group (XX). Here, HLA-DRB1 is linked to rheumatoid arthritis.