Caring for Crohn's & UC

IBD & Genes: A confusing relationship

December 6, 2012 at 9:15 pm Rebecca K. 4 comments

In a recent post about IBD myths, I talked about how while there is some genetic relationship with IBD, there is no one gene that can be tied to the diseases. Today’s post is about how wrong I was about that!

I did a little digging around about genes associated with IBD and found some pretty interesting information. So here is my attempt to digest the extremely scientific information into something concise and understandable (and please forgive me if I get some of it wrong or if my explanation is confusing!).

Last month, researchers at the National Institutes of Health discovered 71 new genes associated with bowel diseases. That brings the number of genes associated with IBD up to 163. That is a whole lot of genes associated with these diseases- way more than I imagined there would be.

It’s important to note that while these genes are associated with IBD, it does not mean that if you have one of these genes, you will develop the disease. What it means is that you have an increased risk of developing Crohn’s or UC.

For this study, DNA samples were taken from people with Crohn’s Disease (20,076), Ulcerative Colitis (15,307), and people without either disease (25,445) from 15 countries. These samples were analyzed and showed the 71 genes that are associated with Crohn’s and UC.

Of the 163 genes now associated with IBD, 110 are associated with Crohn’s Disease and Ulcerative Colitis. Thirty genes are specific to Crohn’s Disease and 23 are specific to Ulcerative Colitis.

According to Cedars-Sinai, the number of genes now associated with IBD is

“significantly more genes than have been identified for any other complex genetic condition.”

Cedars-Sinai also reports that:

“In addition to uncovering the link between IBD and other immune disorders through these genes, the new research also suggests overlap between IBD susceptibility genes and genes tied to the immune system’s response to mycobacterial infections, including tuberculosis and leprosy. This suggests that the ability of humans to resist these infections over many thousands of years may have resulted in the presence of these genetic variants that increase the risk of IBD.”

Genes associated with Crohn’s Disease

There are a few genes that are specifically associated with Crohn’s Disease. They include:

• ATG16L1: The NIH reports that “At least one variation in the ATG16L1 gene is associated with an increased risk of Crohn’s disease, particularly a form of the disorder that affects the lower part of the small intestine (the ileum).”

• NOD2: There are approximately 40 variations of this gene that can be linked to an increased risk of developing Crohn’s. According to the NIH, “Studies suggest that changes in the NOD2 gene prevent the protein from recognizing bacteria, allowing these microbes to grow unchecked and invade cells that line the intestine. An abnormal immune response to these bacteria may contribute to chronic inflammation and the digestive problems characteristic of Crohn disease.”

• IL23R: The NIH reports that several variations of this gene influence the risk of developing Crohn’s. However, “Although it is unclear how this change protects against Crohn’s disease, researchers believe that the receptor’s role in triggering inflammation in the intestinal walls may underlie its connection with this disorder.”

• IRGM: Some variations of this gene are associated with an increased risk in developing Crohn’s. Specifically, “Researchers suspect that changes involving the IRGM protein may disrupt the autophagy process, preventing the immune system from destroying harmful bacteria effectively. An abnormal immune response to bacteria in the intestinal walls may lead to chronic inflammation and the digestive problems characteristic of Crohn’s disease.”

There are also some chromosome variations that can be associated with Crohn’s Disease.

• Chromosome 5: There are several parts of Chromosome 5 that are associated with an increased risk of developing Crohn’s. Some of the regions contain other genes that may influence Crohn’s Disease risk, including SLC22A4 and SLC22A5. The NIH writes, “For example, a combination of genetic variations in a region of DNA on the long (q) arm of the chromosome (5q31) has been shown to increase a person’s chance of developing Crohn disease. Together, these variations are known as the inflammatory bowel disease 5 (IBD5) locus.”

• Chromosome 10: Similar to Chromosome 5, variations in a part of Chromosome 10 have been associated with a risk of developing Crohn’s. According to the NIH, “Researchers refer to this part of chromosome 10 as a “gene desert” because it contains no known genes. However, it may contain stretches of DNA that help regulate nearby genes such as ERG2. This gene has a potential role in immune system function, and researchers are interested in studying the gene further to determine whether it is associated with Crohn’s disease risk.”

Genes associated with Ulcerative Colitis

Unfortunately, in my brief research, I couldn’t find specific genes mentioned that are associated with Ulcerative Colitis like I did for Crohn’s. That being said, there are some chromosomes that have a link to Ulcerative Colitis including chromosomes 16, 12, 6, 14, 5, 19, 1, and 3.  However, none of these have been shown consistently at fault (NOTE: this information came from Wikipedia, I am not sure how reliable it is).

The bottom line

According to the NIH:

“The inheritance pattern of Crohn’s disease is unclear because many genetic and environmental factors are likely to be involved. This condition tends to cluster in families, however, and having an affected family member is a significant risk factor for the disease.”

Similarly, the NIH writes about Ulcerative Colitis:

“The inheritance pattern of ulcerative colitis is unknown because many genetic and environmental factors are likely to be involved. Even though the inheritance pattern of this condition is unclear, having a family member with ulcerative colitis increases the risk of developing the condition.”

It is obvious that there is a possible genetic link with inflammatory bowel disease. For most of the gene variations, the risk is even more increased among Caucasians and those of Eastern European descent.

However, as I stated earlier, this does not mean that if you have the gene, you will develop Crohn’s or UC. So you shouldn’t worry yourself about whether or not you carry an IBD gene or if you will pass it on to your children because there are too many other factors related to the development of these diseases.

NOTE: All of the scientific information above came from the National Institutes of Health’s Genetics Home Reference.

If I missed anything, please let me know- I’d love to learn more about IBD and genetics!

Entry filed under: Genetics. Tags: crohn's, crohn's disease, Crohn's Sucks, genetics, ibd, uc, ulcerative colitis.