Doctors don’t know exactly what causes ulcerative colitis (UC), a type of inflammatory bowel disease (IBD). But genetics seem to play an important role.

UC runs in families. In fact, having a family history of UC is the biggest risk factor for the disease. It’s likely that people inherit a genetic risk for UC. In addition, certain factors in their environment seem to play a role in their immune system’s attack on their large intestine, setting off the disease.

Families with UC share some common genes. Dozens of genetic variations, or changes, have been linked to the condition. Genes may trigger UC by altering the body’s immune response or disrupting the intestines’ protective barrier.

What’s still unknown is whether genes directly cause the condition, and if so, which ones.

Researchers have looked into several factors that link genetics to an increased risk for UC. These include:

Clusters in families

UC tends to run in families — especially among close relatives. About 10 to 25 percent of people with UC have a parent or sibling with IBD (either UC or Crohn’s disease). The risk of UC is also higher among more distant relatives, like grandparents and cousins. UC that affects multiple family members often starts at an earlier age than it does in people with no family history of the condition.

Twins

One of the best ways to study genes in UC is to look at families.

Twins in particular offer an ideal window into the genetic roots of the disease, because their genes are most similar. Identical twins share most of the same DNA. Fraternal twins share about 50 percent of their genes. Twins who grow up in the same home also share many of the same environmental exposures.

For people who have UC and are an identical twin, research finds that about 16 percent of the time, their twin will also have UC. In fraternal twins, that number is about 4 percent.

Ethnicity

UC is also more common among people of certain ethnicities. Caucasians and Ashkenazi Jews (Jews of European descent) are more likely to have the disease than other ethnic groups.

Genes

Researchers have been looking at dozens of genetic changes that may be involved in UC. They still don’t know how these changes trigger the disease, but they have a few theories.

Some of the genes that have been linked to UC are associated with the body’s ability to produce proteins that form a protective barrier on the surface lining inside the intestine. This barrier keeps normal flora bacteria and any toxins inside the intestine. If this protective barrier is broken, bacteria and toxins may come into contact with the epithelial surface of the large intestine, and this could trigger an immune system response.

Other genes linked to UC affect T cells. These cells help your immune system identify bacteria and other foreign invaders in your body and attack them.

Certain genetic makeups may cause T cells to either mistakenly attack the bacteria that normally live in your intestines or have too aggressive of a response to pathogens or toxins passing through your colon. This excess immune response may contribute to the disease process in UC.

A 2012 study discovered more than 70 susceptibility genes for IBD. Many of these genes had already been associated with other immune disorders, such as psoriasis and ankylosing spondylitis.

Genes play an important role in the development of UC, but they’re just one part of the puzzle. Most people who get this condition have no family history.

In general, IBD affects more people in developed countries, and especially those living in urban areas. Pollution, diet, and chemical exposure may have to do with this increased risk.

Possible triggers that have been linked to UC include:

  • a lack of exposure to bacteria and other germs in childhood, which prevents the immune system from developing normally (called the hygiene hypothesis)
  • a diet that’s high in fat, sugar, and meat and low in omega-3 fatty acids and vegetables
  • vitamin D deficiency
  • antibiotic exposure in childhood
  • use of aspirin (Bufferin) and other nonsteroidal anti-inflammatory drugs (NSAIDs)
  • infections with bacteria and viruses, such as E. coli, Salmonella, and measles

Q:

If my sibling has UC, can I be genetically tested to see if I have it too?

A:

Typically, genetic testing isn’t routinely done to check for UC. A sibling with UC increases your risk for having UC. But because of the many gene variations that may be associated with a higher risk for having UC, there is currently no single genetic test specific for UC.

Making a diagnosis of UC is typically based on a combination of clinical history (family history, past medical history, environmental exposure history, and your gastrointestinal symptoms and signs) and diagnostic tests (usually a combination of blood, stool, and imaging studies).

Stacy Sampson, DOAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.