A September 5, 2014 news item from IFFGD reports that a gene mutation that appears to relate to irritable bowel syndrome has been identified in a genetic region known as SCN5A. SCN5A controls part of the function of the sodium channel, which is necessary for normal gastrointestinal motility.
This news item was based on a study of SCN5A in people with IBS that was published in Gastroenterology in June 2014. The authors included 29 researchers at the Mayo Clinic in Rochester, Minnesota and several other research centers in Sweden, Greece and Italy. The study involved genotype analysis of 584 people with IBS and 1380 people without IBS as controls. 2.2% of the people with IBS showed SCN5A encoding errors which disrupted sodium channel function. Interestingly, although diarrhea-predominant IBS was the most common subtype found in the study group with IBS, more of those found to have the SCN5A mutations were constipation-predominant rather than other IBS subtypes. Mexiletine, an anti-arrythmic drug used in restricted situations for certain cardiac conditions, resolved the disruption of the sodium channel when used on isolated cells in the laboratory. One person with IBS-C who was given mexiletine as a medication during the study also had a normal bowel pattern afterward. The overall findings of this study have been replicated 4 separate times with a total of 1745 people with IBS and unaffected control groups.The authors conclude that they have identified one mechanism of IBS and potential future treatment of it.
It should be emphasized that 2.2% is a very small subset of all people with IBS and this gene mutation is not necessarily the only potential factor leading to IBS symptoms, even in those who are eventually found to have it. At this time, it can only be identified in a research context, and cannot be tested or treated by physicians in a clinical setting. There is no single “IBS gene” that causes IBS in all people who develop it. Anecdotally, many people with IBS know that they have genetic relatives who also have IBS or commonly overlapping conditions, but many others with IBS have no known family history of the condition. There are many possible areas of continuing research into the causes of IBS. However, as with many advances over the past few years, this mutation in SCN5A is a promising partial answer and a potential source of hope for a small subset of people whose IBS cannot be adequately managed by currently available means.