Ulcerative colitis (UC) appears to run in families, suggesting that genetic factors may play a role. In addition, scientists have identified changes in a number of genes that may contribute to the development of UC.

However, experts are still working to establish the precise role specific genes play, if any.

While the exact cause of UC for each individual is unknown, experts believe that it results from an abnormal immune response or changes in the protective barrier of the intestine.

There is also a complex interplay of genetic susceptibility and environmental triggers. These may make a person more likely to develop an inappropriate immune response, resulting in inflammatory bowel disease (IBD) such as UC or Crohn’s disease.

This article discusses the genetic factors linked with ulcerative colitis and other triggers that may set off the disease.

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Ulcerative colitis is a long-term condition affecting the gastrointestinal tract.

UC is a form of IBD and is an autoimmune condition. A fault in the immune system may cause the body to mistakenly attack healthy cells and fight nonexistent infections — viral or bacterial — leading to chronic inflammation in the inner surface of the colon. This inflammation results in sores, which doctors refer to as ulcers, developing in the intestines.

Symptoms vary from person to person, but they generally include:

People with UC will have periods of active disease, known as flares, and periods of remission, when they may not experience any symptoms.

Learn more from our IBD hub about living with ulcerative colitis.

A 2017 study found 242 susceptibility loci – DNA sequence – for IBD. Experts associated 50 of these with very early onset inflammatory disease. A 2019 study also found six genes responsible for the progression of UC.

UC also shares a genetic architecture with multiple sclerosis, another autoimmune-mediated disease, according to a 2021 study.

There are also other factors linking genetics to an increased susceptibility to having UC, including:

Family history

A 2018 study stated that having a first-degree relative with UC such as a parent, sibling, or offspring, increases the risk of having UC within the family.

This study also demonstrates that 8–12% of people with IBD report a positive family history. Although, they concluded that Crohn’s disease may show a more frequent familial pattern than UC.

This study also described a cumulative effect, with the highest incidence reported in families where the disease affects three or more family members.

Twin studies

Since identical twins (monozygotic) share the same genetic material, twin studies help researchers understand which traits are due to genes and which are the result of environmental factors.

The risk for identical twins is significantly higher for Crohn’s than for UC. While in non-identical (dizygotic) twins the rates are lower for both forms of IBD.

The study also mentioned that children with parents who both have IBD have a higher risk.

Ethnicity

The frequency of UC is much higher in certain ethnic groups.

The Ashkenazi Jewish population has a fourfold increased risk of IBD. Researchers considered to have a higher risk of IBD if a first, second, or more distant relative had a diagnosis of Crohn’s or UC.

IBD is also more common in white people than people of African and Asian descent.

However, a meta-analysis showed a higher incidence of UC in people of South Asian descent who had immigrated to the United Kingdom and Canada. In this instance, environmental factors may play a more significant role in determining UC than other triggers.

Gender

Generally, IBD affects males and females equally. However, those diagnosed with UC when older are more likely to be males.

However, research from 2019 suggests that UC is more common in males than in females. In addition, males are more likely to receive a diagnosis between 50 and 60 years old.

A person’s environment seems to also play a role in increasing their risk of developing UC. Other triggers may relate to a person’s health and treatments from a young age, lifestyle, and levels of stress a person may experience.

Environment

A study from 2017 demonstrated that people living in rural households might have a lower risk of both UC and Crohn’s than those in urban residences.

These comparisons of a person’s environment relate to:

  • population size
  • population density
  • economic and social factors from neighboring regions

Lifestyle

Smoking has a stronger link with Crohn’s disease than UC. However, a 2021 study found a 2.3-fold risk of UC in current smokers. Another 2021 study also found a potential positive association between UC and the age when a person started smoking.

Diet may also trigger UC. Research from 2019 shows the effects of one type of diet, the Western-style diet (WSD), on a person’s likelihood of developing IBD. In the long term, the number of refined carbohydrates present in the WSD may alter the gut microbiota, increasing the risk for many diseases, including IBD.

The study showed that the fecal microbiota of people on a specific carbohydrate diet had a higher biodiversity index — a healthier gut environment — than people eating a WSD.

A 2021 study also found that a low-fat and high-fiber diet may reduce inflammation markers in UC, leading to improved quality of life.

Read about diets for people with UC here.

Stress

A 2016 study found a bi-directional relationship between stress and depression and IBD. A 2022 study also found that inflammation in the central nervous system can trigger depressive symptoms.

Experts believe that the gut-brain axis plays a crucial role in the disease progression and relapse of IBD symptoms.

Read more on UC and the gut-brain link here.

Childhood

A 2016 study found that taking antibiotics in childhood and adolescence increases a person’s risk of IBD, namely Crohn’s.

Both forms of IBD may also occur in people who drank breast milk as a baby because breast milk influences a child’s microbiome.

Other possible triggers linked to UC include:

Doctors do not routinely request genetic testing to diagnose UC in current practice.

UC has no specific genetic test checks, especially since medical professionals associate many gene variations with the disease.

However, genetic markers show a great potential to identify the outlook and treatment outcomes of people with IBD. A 2019 study found genetic variants linked with medication side effects in people with IBD.

Ulcerative colitis is a chronic condition which may affect a person’s quality of life.

It has no known cure. However, treatments can help induce remission and reduce the severity of its symptoms. Most people require ongoing medications and lifestyle changes, while some may need surgery.

Current studies aim to better understand the biological processes that drive the disease to develop strategies that can help prevent its progression.

Ulcerative colitis is a complex disease caused by genetic and environmental factors. Certain genes put a person at risk of developing the disease. If a parent or sibling has UC this increases the risk of developing the condition within the family.

While it runs in families, it is crucial to understand that UC can occur in anyone, even in people with no family history of UC. There are other factors to consider, such as the environment someone grows up in, their lifestyle, factors such as stress and diet, along with other possible triggers.