Autoimmune disorders constitute a diverse group of phenotypes with overlapping features and a tendency toward familial aggregation. It is likely that common underlying genes are involved in these disorders. Until very recently, no specific alleles--aside from a few common human leukocyte antigen class II genes--had been identified that clearly associate with multiple different autoimmune diseases. In this study, we describe a unique collection of 265 multiplex families assembled by the Multiple Autoimmune Disease Genetics Consortium (MADGC). At least two of nine "core" autoimmune diseases are present in each of these families. These core diseases include rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), type 1 diabetes (T1D), multiple sclerosis (MS), autoimmune thyroid disease (Hashimoto thyroiditis or Graves disease), juvenile RA, inflammatory bowel disease (Crohn disease or ulcerative colitis), psoriasis, and primary Sjogren syndrome. We report that a recently described functional single-nucleotide polymorphism (rs2476601, encoding R620W) in the intracellular tyrosine phosphatase (PTPN22) confers risk of four separate autoimmune phenotypes in these families: T1D, RA, SLE, and Hashimoto thyroiditis. MS did not show association with the PTPN22 risk allele. These findings suggest a common underlying etiologic pathway for some, but not all, autoimmune disorders, and they suggest that MS may have a pathogenesis that is distinct from RA, SLE, and T1D. DNA and clinical data for the MADGC families are available to the scientific community; these data will provide a valuable resource for the dissection of the complex genetic factors that underlie the various autoimmune phenotypes.

Objective: To determine whether the impact of tobacco exposure on rheumatoid arthritis (RA) risk is influenced by polymorphisms at the HLA-DRB1 and glutathione S-transferase M1 (GSTM1) loci. Methods: Subjects were participants from a case-control study nested within the Iowa Women's Health Study, a population based, prospective cohort study of postmenopausal women. Incident RA cases (n = 115) were identified and medical records reviewed to confirm RA diagnosis. Controls without RA (n = 466) were matched with RA cases by age and ethnic background. HLA-DRB1 typing classified subjects according to the presence of alleles encoding the RA ''shared epitope'' (SE) sequence. GSTM1 was genotyped using a multiplex polymerase chain reaction assay. Conditional logistic regression was used to estimate the odds ratios (ORs) and 95% confidence intervals. Results: Strong positive associations of smoking (OR = 6.0, p = 0.004), SE positivity (OR = 4.6, p = 0.0006), and GSTM1 null genotype (OR = 3.4, p = 0.007) with risk of RA, and significant geneenvironment interactions (smoking by SE interaction p = 0.034; smoking by GSTM1 interaction p = 0.047) were observed. Stratified analyses indicated that exposure to tobacco smoke primarily increased the risk of RA among subjects who lacked genetic risk factors for the disease (that is, SE negative or GSTM1 present). Conclusions: Although these findings require confirmation in other groups, the results support the importance of considering both genetic and environmental factors, and also their interaction, in studies of complex diseases like RA.