Genes are of little importance in the development of rheumatoid arthritis, finds a study in this week's BMJ.
Researchers in Denmark surveyed over 37,000 twins about rheumatic diseases. Twin studies are one of the simplest ways to unravel the relative importance of genetic and environmental effects of a disease. Twins who reported that they had rheumatoid arthritis were invited to have a clinical examination.
Rheumatoid arthritis was verified in 13 identical and 36 non-identical twins. No identical twins and only two pairs of non-identical twins both had rheumatoid arthritis, suggesting that rheumatoid arthritis is no more common in identical twins than non-identical twins.
Despite some study limitations, the authors conclude that environmental effects may be more important than genetic effects in the development of rheumatoid arthritis.
This study cannot disprove a genetic component in susceptability to rheumatoid arthritis, writes Professor Alan Silman in an accompanying commentary. However, the results emphasise that the genetic effects are weak compared with environmental ones in explaining differences in occurrence of disease.