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To investigate whether smoking and HLA–DR shared epitope (SE) genes may interact in triggering immune reactions to citrulline‐modified proteins. In a case–control study involving patients with recent‐onset rheumatoid arthritis (RA), we studied interactions between a major environmental risk factor (smoking), major susceptibility genes included in the SE of HLA–DR, and the presence of the most specific autoimmunity known for RA (i.e., antibodies to proteins modified by citrullination). Immunostaining for citrullinated proteins in cells from bronchoalveolar lavage fluid was used to investigate whether smoking is associated with citrullination in the lungs.Previous smoking was dose‐dependently associated with occurrence of anticitrulline antibodies in RA patients. The presence of SE genes was a risk factor only for anticitrulline‐positive RA, and not for anticitrulline‐negative RA. A major gene–environment interaction between smoking and HLA–DR SE genes was evident for anticitrulline‐positive RA, but not for anticitrulline‐negative RA, and the combination of smoking history and the presence of double copies of HLA–DR SE genes increased the risk for RA 21‐fold compared with the risk among nonsmokers carrying no SE genes. Positive immunostaining for citrullinated proteins was recorded in bronchoalveolar lavage cells from smokers but not in those from nonsmokers.We identified an environmental factor, smoking, that in the context of HLA–DR SE genes may trigger RA‐specific immune reactions to citrullinated proteins. These data thus suggest an etiology involving a specific genotype, an environmental provocation, and the induction of specific autoimmunity, all restricted to a distinct subset of RA. [ABSTRACT FROM AUTHOR]

Abstract An editorial in this issue explains that the degree of biological interaction between risk factors is measured as the deviation from additivity by the corresponding disease rates and not for example as deviation from multiplicativity. It is the purpose of this article to describe how a logistic regression model, or a Cox regression model, can be defined in order to produce the output that is needed for assessment of biological interaction. We will also demonstrate how common software can be programmed to deliver this output. Finally, we show how this output can be used as input in an Excel sheet that is set up to calculate the measures of biological interaction to be used for the assessment. [ABSTRACT FROM AUTHOR]

The main genetic risk factor for rheumatoid arthritis (RA) is the shared epitope (SE) of HLA–DR, while smoking is an important environmental risk factor. We studied a potential gene–environment interaction between SE genes and smoking in the etiology of the 2 major subgroups of RA: rheumatoid factor (RF)–seropositive and RF‐seronegative disease. A population‐based case–control study involving incident cases of RF‐seropositive and RF‐seronegative RA (858 cases and 1,048 controls) was performed in Sweden. Cases and controls were classified according to their cigarette smoking status and HLA–DRB1 genotypes. The relative risk of developing RA was calculated for different gene/smoking combinations and was compared with the relative risk in never smokers without SE genes.The relative risk of RF‐seropositive RA was 2.8 (95% confidence interval [95% CI] 1.6–4.8) in never smokers with SE genes, 2.4 (95% CI 1.3–4.6) in current smokers without SE genes, and 7.5 (95% CI 4.2–13.1) in current smokers with SE genes. Smokers carrying double SE genes displayed a relative risk of RF‐seropositive RA of 15.7 (95% CI 7.2–34.2). The interaction between smoking and SE genes was significant, as measured by the attributable proportion due to interaction, which was 0.4 (95% CI 0.2–0.7) for smoking and any SE, and 0.6 (95% CI 0.4–0.9) for smoking and a double SE. Neither smoking nor SE genes nor the combination of these factors increased the risk of developing RF‐seronegative RA. The disease risk of RF‐seropositive RA associated with one of the classic genetic risk factors for immune‐mediated diseases (the SE of HLA–DR) is strongly influenced by the presence of an environmental factor (smoking) in the population at risk. [ABSTRACT FROM AUTHOR]

To study the frequency of allele A of polymorphism PD‐1.3 of the PDCD1 gene in patients with rheumatoid arthritis (RA) and its subsets, based on the presence of rheumatoid factor (RF) and the shared epitope (SE) alleles.A total of 1,175 patients with RA and 3,404 controls were genotyped for the PD‐1.3 A/G polymorphism, which previously was identified as being involved in susceptibility to systemic lupus erythematosus (SLE) in patients of European descent.We first detected a trend for association of allele A of the single‐nucleotide polymorphism PD‐1.3 with RA (P = 0.053, odds ratio [OR] 1.18, 95% confidence interval [95% CI] 0.99–1.41). To further clarify the nature of this association, patients with RA were divided into 4 groups according to the presence of RF and the SE alleles. Association was found only in the group of patients negative for both RF and the SE alleles (P = 0.0054 [corrected P = 0.015], OR 1.75, 95% CI 1.15–2.65).Patients negative for both RF and the SE alleles showed association with the same allele that we previously identified as being involved in susceptibility to SLE. These results provide the first evidence of the involvement of the human PDCD1 gene in arthritis. [ABSTRACT FROM AUTHOR]

The relative risk of disability pension due to musculoskeletal disorders has been studied with regard to occupation and work load. The study population comprised men born 1915 to 1934, living in Stockholm county. 1307 men who received a disability pension during 1979, 1980, 1981 and 1984 due to disorders from the low back, neck/shoulder, hip, and knee were compared with 298 randomly selected men concerning occupation and occupational work load. Disability pensions were more common both in men with medium and high physical work load compared to men with low physical work load. Construction workers and metal workers had a high relative risks of receiving disability pensions because of disorders in all four body regions, and men in many other occupations had disorders in two or three regions. In office workers the risk of disability pension because of musculo-skeletal disorders was low. [ABSTRACT FROM PUBLISHER]