GSTM1 and rheumatoid arthritis: Since most mentioned previously published studies were cross sectional with long lasting RA (median 11 years [16], <5 years [23], 7 years [19]) and our study was preformed in incident cases, differences in results may have occurred due to an influence of GSTM1 variations on disease development and thus on which cases were available for recruitment in a long-lasting RA population.