Rheumatoid arthritis in Poland and Lithuania: different clinical course and HLA associations despite similar genetic background

A recognised feature of rheumatoid arthritis (RA) is its clinical heterogeneity, which may be caused by HLA factors. This theory is supported by observations that relatively severe and mild RA are associated with, respectively, DRB1*041 and DRB1*01.2–4 Further, comparisons between populations show that the disease course in the Mediterranean is milder than in northern Europe,5–8 correlating with a higher frequency of DRB1*01 and lower frequency of DRB1*04 in the former than in the latter region.6,7,9 Poland and Lithuania are neighbouring central European countries. During clinical practice we noted that RA was less severe in Lithuanian than in Polish patients. To test this observation we prospectively analysed 24 Polish and 20 Lithuanian randomly recruited patients with recent onset RA …