Rheumatoid arthritis affects about 1.3 million Americans. Women are more likely to have this chronic autoimmune disease than men at a rate of 70 per cent compared to 30 per cent.

When you have RA your immune system doesn't function properly. White blood cells that normally protect your body from infection start to attack your body's healthy tissue, mistaking it for a foreign invader. This reaction causes swelling, pain and fever, which are all symptomatic of inflammation. Over the long term inflammation damages the joints, and at the extreme can also harm organs.

Better understanding of the causes and activity of RA allows health professionals to more effectively treat it - and maybe to one day, a cure.

What is a genetic marker?

The National Human Genome Research Institute defines a genetic marker as a segment of DNA with an identifiable physical location on a chromosome whose inheritance can be followed. It can be a gene, or a section of DNA with no known function. It can be used to track the inheritance pattern of genes that have not yet been identified, but whose approximate locations are known.

Evidence of the roles of genetic markers in RA

Several genetic markers have been associated with a heightened risk of getting rheumatoid arthritis. However, scientists are unable to make a causal relationship between any marker and RA. Some studies have shown that while a marker may be factors for people with RA in one country, they may not play a role in arthritis sufferers somewhere else.

The first gene strongly associated with RA is called the HLA shared isotope. It lies in the HLA region, which is found on white blood cells and controls immune responses. The Arthritis Foundation reports that people with this genetic marker are five times more likely to develop RA than people who do not have it. More than 66 per cent of white Americans with RA have the shared epitope compared to only 20 per cent of the general population.

Since that landmark discovery, other genes have been implicated in RA development or activity. HLA-DR4 is one of them, and it's also associated with Lyme disease, an arthritis-related condition transmitted through deer ticks. People with the HLA-DR4 gene have more severe forms of RA and respond poorly to antibiotic treatment.

In a recent study conducted the North American Rheumatoid Arthritis Consortium (NARAC) analyzed DNA from 2,500 patients with RA or lupus. Through genetic mapping researchers were able to identify STAT4 on chromosome 2 as a culprit in the risk of developing both diseases. In America this particular form of STAT4 increases the risk of developing RA by 30 per cent.

In another study reported in Arthritis & Rheumatism, researchers discovered that men with rheumatoid arthritis were more likely to have a gene called HLA-DBR1, a subtype of the genetic marker HLA-DR4. Also, women with brothers who had RA were more likely to have the gene than women whose brothers didn't have RA. This gives even more strength to the idea that this autoimmune disease runs in families.