Coeliac disease is an autoimmune condition with a strong genetic component, but genetics alone do not explain why the disease develops.
Many people carry the genes associated with coeliac disease and eat gluten throughout their lives without ever developing the condition. For coeliac disease to occur, several things need to happen.
Understanding how genetics, gluten exposure and environmental influences work together helps explain why some people develop coeliac disease while others do not.
This page explains the role of genetics and the factors currently believed to contribute to the development of coeliac disease.
THE GENES LINKED TO COELIAC DISEASE
Coeliac disease is genetic and a lifelong autoimmune condition. There is currently no cure, and it does not go away over time.
Most people with coeliac disease carry specific immune system genes called HLA-DQ2 or HLA-DQ8.
These genes affect how the immune system recognises certain proteins, including gluten. When people with these genes consume gluten, the immune system may mistakenly attack the lining of the small intestine, if you have diagnosed coeliac disease.
However, having these genes does not mean someone will develop coeliac disease. They simply indicate that a person has the genetic potential for the condition.
Genetic testing should be used during the diagnostic process because a negative gene test makes coeliac disease very unlikely.
Further information about genetic testing:
MANY PEOPLE CARRY THE GENES
Genes linked to coeliac disease are very common in the general population.
Research shows that:
- In Australia, up to approximately 50% of people carry HLA-DQ2 and/or HLA-DQ8
- of these people, about 1 in 40 will develop coeliac disease
- an immediate family member (parent, sibling or child) of someone with coeliac disease has a 1 in 10 chance of developing it as well
- currently, 1 in 70 people in Australia have coeliac disease, however, 80% remain undiagnosed
This means that most people with the genes will never develop the condition, however there is that unknown factor of those who remain undiagnosed.
Coeliac Australia explains that approximately half of the population carries these coeliac genes, yet only a small proportion develop the disease.
Further information:
- Coeliac Australia – Diagnosis and genetic testing (external)
- Distribution of HLA-DQ2/DQ8 in a Danish population (external)
WHY GLUTEN IS REQUIRED
Coeliac disease only develops in people who consume gluten.
Gluten is a group of proteins found in wheat, rye and barley (with oats containing a very similar protein called avenin). In people with coeliac disease, gluten triggers an immune response that damages the lining of the small intestine.
However, gluten exposure alone does not explain the disease. If it did, many more people would develop coeliac disease because gluten consumption is widespread and the genes are common.
Instead, research suggests that coeliac disease develops when genetic susceptibility, gluten exposure and other factors occur together.
Further information:
โ Read: Understanding coeliac disease
POSSIBLE ENVIRONMENTAL TRIGGERS
Researchers believe that additional environmental factors may influence whether coeliac disease develops in people who carry the genes.
Possible contributing factors currently being studied include:
- certain viral and digestive system infections
- changes in the gut microbiome
- changes in hormones, such as pregnancy, child birth or perimenopause
- severe emotional or physical stress
- other environmental or immune system influences
These factors may affect how the immune system reacts to gluten in genetically susceptible people.
It is important to note that no single trigger explains every case, and research in this area is ongoing.
Further reading:
โ Read: Newly diagnosed with coeliac disease
WHAT GENETIC TESTING CAN AND CANNOT TELL YOU
Genetic testing for HLA-DQ2 and HLA-DQ8 may sometimes be used to help rule out coeliac disease.
Important points about gene testing include:
- a positive gene result does not diagnose coeliac disease
- many healthy people carry these genes
- a negative result makes coeliac disease extremely unlikely
For this reason, genetic testing is usually used as one part of the diagnostic process, rather than as a stand-alone test.
HAVING THE GENE DOES NOT MEAN THE DISEASE IS โINACTIVEโ
It is common to hear people describe coeliac disease as a gene that is โactivatedโ or โnot activatedโ. However, this is not how coeliac disease works.
The genes associated with coeliac disease indicate genetic susceptibility, not whether the disease is active or inactive.
A person may:
- carry the genes but never develop coeliac disease
- carry the genes and later develop coeliac disease
- not carry the genes and therefore be very unlikely to develop coeliac disease
Blood tests (such as antibody tests) measure the immune systemโs response to gluten, not whether a gene has been โactivatedโ.
In coeliac disease, the genes (HLA-DQ2 or HLA-DQ8) determine whether the immune system has the potential to react to gluten. However, they do not cause the immune response on their own.
The immune response only occurs when:
- a person has the genetic susceptibility
- gluten is being consumed
- the immune system is actively reacting
This is why someone can carry the genes but have:
- normal blood tests
- no intestinal damage
- no diagnosis of coeliac disease
Once coeliac disease develops, the immune system produces antibodies in response to gluten, which is what blood tests detect.
This means that genetic testing and blood tests are measuring two different things:
- genetic testing shows whether a person is at risk
- blood tests show whether the immune system is actively reacting to gluten
Coeliac disease is not a gene that switches on and off, but an immune condition that develops when several factors come together.
SUMMARY: WHY COELIAC DISEASE DEVELOPS
Current evidence suggests that coeliac disease usually develops when several factors occur together:
- genetic predisposition (HLA-DQ2 or HLA-DQ8)
- exposure to gluten
- additional environmental or immune triggers
Many people carry the genes associated with coeliac disease, but most never develop the condition.
This is why coeliac disease is considered a complex autoimmune condition, influenced by both genetics and environmental factors.
โ Read: Everyday gluten free living
WHAT TO READ NEXT
Understanding genetics is just one part of the picture. You may also find it helpful to explore: