Genetics of Axial Spondyloarthritis

Genes are passed down from parents to their children. They are composed of DNA that dictates things like your eye color and your height. Genes also play a role in risk for certain diseases.¹

Scientists have found several genes that are linked to axial spondyloarthritis (axSpA), a type of arthritis that mainly affects the spine. Researchers are still working to understand all the ways that genes may be involved in the condition. This knowledge is helping them develop better treatments.²

HLA-B27

HLA-B27 is a protein found on the surface of white blood cells. This genetic marker is involved in the immune response. It is also linked to certain autoimmune diseases. It is commonly found in radiographic axSpA, also called ankylosing spondylitis (AS).³

People who have the HLA-B27 protein and are diagnosed with AS are more likely to have:⁴

• Bony growths of the spine, which could lead to the bones growing together (fusion)
• Severe damage to the spine and joints around the spine, seen on X-ray

It is important to understand that many people who are HLA-B27 positive will never develop axSpA or AS. Also, many who are HLA-B27 negative are diagnosed with axSpA or AS. This is confusing for many, including the doctors who treat and manage axSpA. More studies are needed to understand the relationship between HLA-B27 and axSpA.²

ERAP1

The endoplasmic reticulum aminopeptidase 1 (ERAP1) gene helps the immune system by reducing how many chemical signals can be sent into cells. This affects how your body deals with inflammation.⁵

ERAP1 also breaks down proteins into smaller pieces that your immune system can recognize. If your immune system sees something it thinks is a virus or bacteria, it will tell the infected cell to destroy itself.⁵

ERAP1 is important for the normal functioning of the immune system. It also helps protect the body against autoimmune disorders and cancer. But changes (mutations) in the ERAP1 gene have been found to increase the risk of AS. Other factors, like the environment or other genes, likely add to this risk.⁵

IL1A

The interleukin-1 alpha (IL1A) gene makes a protein of the same name. This protein is part of a group of proteins known as interleukins. These proteins are part of the body's immune system. IL1A proteins promote inflammation to help the immune system fight foreign substances such as viruses.⁶

Studies have shown that people with a mutation on the IL1A gene are more likely to develop axSpA than those without the mutation. But not everyone with the IL1A mutation will develop axSpA. It is unclear why some people are affected while others are not.^6,7

The IL1A genetic marker is an important clue in our knowledge of this complex disorder. But more research is needed to understand it better.^6,7

IL23R

The IL23R gene is responsible for making interleukin 23 (IL23) receptors. IL23 receptors sit on the outside of immune system cells, waiting for other IL23 proteins to fit in them like a key in a lock.⁸

IL23 proteins help the body to recognize bacteria, viruses, and other diseases. When the proteins join with the receptors, they create inflammation to help the body fight off infections.⁸

Variations in IL23R genes may rearrange many of the building blocks of IL23 receptors. Some of these changes may lead to axSpA.^7,8

There is still much to know about how genes relate to axSpA. More studies are needed to get exact answers. Talk to your doctor about your genetic risks and how they may connect to axSpA.