Understanding the causes of rheumatoid arthritis

Despite a great deal of research, the actual reasons why people develop rheumatoid arthritis remain unknown. The possible causes can broadly be divided into, those factors which are inherited and those factors which are encountered in our environment.

There is a tendency for rheumatoid arthritis to run in families. If one of a pair of identical twins has rheumatoid arthritis then the other has a 16% chance of developing the disease. This is substantially higher than the risk in the general population, which is approximately 0.8%.

Since identical twins have identical genes, the presence of the same traits in both twins exists and this high degree of what is called 'concordance', points to a major genetic contribution to the cause of rheumatoid arthritis. Yet, no single gene has been identified as the certain cause for the development of rheumatoid arthritis.

Similarly, there is no single environmental factor which is sufficient, by itself, to cause rheumatoid arthritis. However, throughout the world, rheumatoid arthritis is more common in women than in men. This suggests that hormonal factors may play a part in the development of the disease.

There has always been a widely held belief that rheumatoid arthritis is caused by an infection, but researchers have been unable to identify this as a cause. In a substantial proportion of cases, rheumatoid arthritis begins within a few weeks of an infection of some sort.

The risk of developing rheumatoid arthritis is higher in smokers. People with rheumatoid arthritis who continue to smoke are also more likely to develop what is called extra-articular disease (nodules, involvement of the lung or inflammation of the blood vessels).

In people with many of the genetic risk factors for rheumatoid arthritis, exposure to a single environmental risk factor may trigger the disease. However, in the majority of people these factors (and others which have not yet been identified) probably act cumulatively, slowly lowering the threshold for the development of rheumatoid arthritis.

Roche researchers have helped to drive advances in our knowledge of rheumatoid arthritis with their investigations during the 1990s. This research has already resulted in the discovery of innovative new therapies and potential therapeutic targets. Today, we continue to deepen our understanding of the immune system and rheumatoid arthritis with the aim of fulfilling our ambition of developing even more personalised solutions to tackle the disease.