Over the last few years, researchers have found some of the genes that are important in IBD. One of these is called CARD15: changes in this gene may be present in up to 30% of people with Crohn's disease (CD). 

This gene is not important in the development of Ulcerative Colitis (UC), and is not relevant in some parts of the world. For instance, it is not important in Japanese people with CD.

The CARD15 gene makes a protein that is important in the responses of the surface of the bowel to bacteria. Changes in the gene lead to abnormal responses from the surface of the bowel, which leads to inflammation.

The other genes which seem to be important in CD also affect how the surface of the bowel responds to foreign materials.

At present tests for genes are not routinely available. Many researchers around the world are doing studies to work out more about the genes in IBD. Over time, we should understand more about these important parts to the cause of IBD.

Because of the importance of genes in the development of IBD, it is not surprising that IBD can run in families. In around 30% of people diagnosed with IBD, there is someone else in their family with IBD. Also, IBD is seen more commonly in twins.

In health, the digestive tract is home to billions of bacteria. Many of the bacteria have vital roles, such as breaking down food and destroying harmful waste products of food digestion.

For some time, it has been clear that the bacteria in the bowel play important roles in the development of IBD. Researchers have tried to see if people with IBD have had any particular infection; however, no specific bacteria or virus infection has been identified to-date.

Groups from Europe and North America have shown that there are big differences between the patterns of bacteria in the digestive tract of people with IBD compared to people without IBD. The cells in the lining of the GI tract in healthy people recognise and interact with these bacteria.

It has been suggested that living in very clean conditions, such as in Western society, changes the type of bacteria in your intestine and this may increase your likelihood of developing IBD. This is called the 'hygiene hypothesis', however this is yet to be proven as a definitive cause of IBD.

The surface of the bowel has many functions in defending the body from invasion. These include keeping GI cells held tightly together, production of mucus, secretion of numerous proteins and development of other responses.

In the healthy body there is a harmony between the bacteria and the lining of the GI tract. If pathogenic (harmful) bacteria get into your intestine, the body's defences swing into action to clear the pathogenic bacteria as quickly as possible.

Once the pathogenic bacteria are cleared, the body's defences then wind down to return the intestine back to its harmonious state. In IBD, the body's defences become active and don't wind down, even when there are no pathogenic bacteria present. It is this constant and uncontrolled activation of the body's defences that cause the symptoms of IBD.