Smoking interacts with HLA-DRB1 shared epitope in the development of anti-citrullinated protein antibody-positive rheumatoid arthritis: results from the Malaysian Epidemiological Investigation of Rheumatoid Arthritis (MyEIRA)

Table 5 Odds ratios for developing ACPA-positive RA and ACPA-negative RA in subjects exposed to different combinations of smoking and presence of HLA-DRB104:05* or non-HLA-DRB104:05* SE alleles, compared with never-smokers without SE alleles in MyEIRA

ACPA, anti-cyclic citrullinated proteins antibody; AP, attributable proportion due to interaction; Ca/Co, number of exposed cases/number of exposed controls; MyEIRA, Malaysian Epidemiological Investigation of Rheumatoid Arthritis; OR (95% CI), odds ratio and 95% confidence interval, adjusted for ethnicity, formal education, age, sex, residential area, calculated by means of unconditional logistic regression to increase power; RA, rheumatoid arthritis; SE, shared epitope. ^a HLA-DRB1*04:05 group was defined by the presence of either one or two copies of HLA-DRB1*04:05 allele. ^bIndividuals with first allele of HLA-DRB1*04:05 and second allele of a non-HLA-DRB1*04:05 SE (that is, HLA-DRB1*04:05/non-HLA-DRB1*04:05 SE) were not included in the interaction analysis (cases, 13; control, 1). ^cAny non-HLA-DRB1*04:05 SE alleles group was defined by the presence of either one or two copies HLA-DRB1*01:01, *01:02, *01:07, *04:01, *04:04, *04:08, *04:10, *10:01, and *10:03 alleles.

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