Date Published: 10 July 2011

Ankylosing Spondylitis (AS), a common auto-immune arthritis research latest

How does an individual's genetic make-up predispose him or her to Ankylosing Spondylitis ?

Ankylosing Spondylitis (AS) is a common auto-immune arthritis which causes pain and stiffness of the spine, and in serious cases, progressive fusion of the vertebrae and other affected joints. Unlike most forms of arthritis, ankylosing spondylitis usually begins in young adulthood, and so can significantly impair the patient's ability to work It oftens involves life-long treatment because there is currently no known cure for ankylosing spondylitis via conventional modern medical techniques. That said, a recently developed group of drugs called TNF blockers are said to show considerable promise in helping alleviate some of the symptoms.

A team of researchers from the Universities of Bristol (pictured on the right)l, Queensland (Australia), Oxford, Texas and Toronto, used a technique called genome-wide association in which millions of genetic markers are measured in thousands of people that have the disease as well as thousands of healthy individuals. Markers which are more frequent in individuals with the disease are more likely to be involved in the condition.

Using this approach the investigators found an additional seven genes likely to be involved in the condition, bringing the total number of genes known to predispose to ankylosing spondylitis to thirteen. Many of the new genes are already known to be involved in inflammatory and immune processes, providing researchers with further clues about how the disease arises. Two of the new genes are also known to predispose to other auto-immune conditions including Crohn's disease (a form of inflammatory bowel disease) and Celiac disease (an auto-immune intestinal disease).

Researchers were also able to demonstrate an interaction between a genetic mutation called HLA-B27 and a mutation in a gene called ERAP1. Specifically, the ERAP1 mutation only predisposed to disease in those individuals who tested positive for the HLA-B27 mutation.

Dr David Evans from Bristol University said:

" This finding is important in a number of ways. First of all it's one of the first convincing examples we have of one mutation influencing the effect of another mutation in the development of a relatively common disease. This is exciting because it implies that there may be other examples of this phenomenon in other common diseases that we don't know about yet.
_ Second, the interaction itself tells us something very fundamental about how ankylosing spondylitis is caused. Prior to this study there were a number of competing theories about how the disease was caused. Our study suggests very strongly which one of these competing hypotheses is likely to be correct."

Finally, the researchers also identified a single genetic marker which could be used to assist in diagnosis of ankylosing spondylitis.

" Ankylosing Spondylitis (AS) is notoriously difficult to diagnose in its early stages which can lead to costly delays in its treatment," said Dr Evans. "Typically diagnosis consists of a combination of X-rays, patient symptoms and expensive immunological assays in the laboratory. This genetic marker could easily take the place of an expensive immunological assay. What would normally cost £40-£50 could be done easily for a fraction of the price."

Reference to Paper:
'Interaction between ERAP1 and HLA-B27 in ankylosing spondylitis implicates peptide handling as the mechanism for HLA-B27 in disease susceptibility' by Evans et al in Nature Genetics

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