We investigated the association between cigarette smoking and the risk of developing rheumatoid arthritis (RA) in the Malaysian population. A total of 1,056 RA patients and 1,416 matched controls aged 18-70 years within a defined area of Peninsular Malaysia were evaluated in a case-control study between August 2005 and December 2009. A case was defined as a person with early diagnosed RA using the 1987 American College of Rheumatology criteria for RA. Controls were randomly selected matched for sex, age, and residential area. Cases and controls answered a questionnaire on a broad range of issues, including lifestyle factors and smoking habits wherein current and former smoking was classified as ever-smoking. The presence of anti-citrullinated peptide antibodies (ACPA) was determined for cases and controls. We found that ever-smokers had an increased risk of developing ACPA-positive RA [odds ratio (OR) = 4.1, 95% confidence interval (CI) 1.9-9.2] but not ACPA-negative RA (OR = 0.7, 95% CI 0.3-2.0), compared with never-smokers. A significant dose-response relationship between cumulative dose of smoking and risk of ACPA-positive RA was observed (<20 pack-years OR = 3.3, 95% CI 1.1-9.8; at least 20 pack-years OR = 5.2, 95% CI 1.6-17.6). Hence, smoking is associated with an increased risk of ACPA-positive RA in the Malaysian population, in which the genetic context is similar to several other Asian countries.
BACKGROUND: To investigate the associations between HLA-DRB1 shared epitope (SE) alleles and rheumatoid arthritis in subsets of rheumatoid arthritis defined by autoantibodies in three Asian populations from Malaysia.
METHODS: 1,079 rheumatoid arthritis patients and 1,470 healthy controls were included in the study. Levels of antibodies to citrullinated proteins (ACPA) and rheumatoid factors were assessed and the PCR-SSO method was used for HLA-DRB1 genotyping.
RESULTS: The proportion of ACPA positivity among Malay, Chinese and Indian rheumatoid arthritis patients were 62.9%, 65.2% and 68.6%, respectively. An increased frequency of SE alleles was observed in ACPA-positive rheumatoid arthritis among the three Asian ethnic groups. HLA-DRB1*10 was highly associated with rheumatoid arthritis susceptibility in these Asian populations. HLA-DRB1*0405 was significantly associated with susceptibility to rheumatoid arthritis in Malays and Chinese, but not in Indians. HLA-DRB1*01 did not show any independent effect as a risk factor for rheumatoid arthritis in this study and HLA-DRB1*1202 was protective in Malays and Chinese. There was no association between SE alleles and ACPA- negative rheumatoid arthritis in any of the three Asian ethnic groups.
CONCLUSION: The HLA-DRB1 SE alleles increase the risk of ACPA-positive rheumatoid arthritis in all three Asian populations from Malaysia.
INTRODUCTION:Rheumatoid arthritis (RA) is a multifactorial autoimmune disease in which genetic and environmental factors interact in the etiology. In this study, we investigated whether smoking and HLA-DRB1 shared-epitope (SE) alleles interact differently in the development of the two major subgroups of rheumatoid arthritis (RA), anti-citrullinated proteins antibody (ACPA)-positive and ACPA-negative disease, in a multiethnic population of Asian descent.
METHODS: A case-control study comprising early diagnosed RA cases was carried out in Malaysia between 2005 and 2009. In total, 1,076 cases and 1,612 matched controls participated in the study. High-resolution HLA-DRB1 genotyping was performed for shared-epitope (SE) alleles. All participants answered a questionnaire on a broad range of issues, including smoking habits. The odds ratio (OR) of developing ACPA-positive and ACPA-negative disease was calculated for smoking and the presence of any SE alleles separately. Potential interaction between smoking history (defined as "ever" and "never" smoking) and HLA-DRB1 SE alleles also was calculated.
RESULTS: In our multiethnic study, both the SE alleles and smoking were associated with an increased risk of developing ACPA-positive RA (OR SE alleles, 4.7; 95% confidence interval (CI), 3.6 to 6.2; OR smoking, 4.1; 95% CI, 1.9 to 9.2). SE-positive smokers had an odds ratio of ACPA-positive RA of 25.6 (95% CI, 10.4 to 63.4), compared with SE-negative never-smokers. The interaction between smoking and SE alleles was significant (attributable proportion due to interaction (AP) was 0.7 (95% CI, 0.5 to 1.0)). The HLA-DRB1*04:05 SE allele, which is common in Asian populations, but not among Caucasians, was associated with an increased risk of ACPA-positive RA, and this allele also showed signs of interaction with smoking (AP, 0.4; 95% CI, -0.1 to 0.9). Neither smoking nor SE alleles nor their combination was associated with an increased risk of ACPA-negative RA.
CONCLUSIONS: The risk of developing ACPA-positive RA is associated with a strong gene-environment interaction between smoking and HLA-DRB1 SE alleles in a Malaysian multiethnic population of Asian descent. This interaction seems to apply also between smoking and the specific HLA-DRB1*04:05 SE allele, which is common in Asian populations but not in Caucasians.