DNA Variants on Chromosome 9 Appear To Be Associated With Irritable Bowel Syndrome (IBS) in Some Women
In April 2018, the journal Gastroenterology published an article that an international collaboration of researchers headed by the Karolinska Institutet in Sweden, has identified several DNA variants on Chromosome 9 that may be associated with higher risk of IBS in women, particularly IBS with constipation. This possible correlation was not found in men. The identified chromosomal regions are similar to those believed to influence the timing of sex hormones, puberty and first menstruation, and may partially explain why known cases of IBS are more common in women than men in most countries of the world.
According to an English-language news summary on the Karolinska Institutet website, these findings were based on extensive data from 300,000 individuals whose genomes were available in the United Kingdom’s Biobank and 2045 people with IBS associated with research and treatment centers in Sweden, Belgium, the Netherlands and the United States. Author information on the journal article in question reveals the involvement of scientists in Sweden, the United States, Australia, Germany, Italy, Spain and the Netherlands. In most of the listed countries, research centers from multiple universities were represented.
While these are exciting discoveries, more research is needed. It should be emphasized that IBS is a complex disorder arising from many factors that likely vary with the individual. The researchers have not identified the specific genes on Chromosome 9, nor is this recent discovery the full answer. Over the past three decades, various studies have established that people with IBS are more likely to have close relatives with IBS than the general population, but the percentages of those self-reporting known family history have varied, and represent only a subset of all people with IBS. It is still not definitively established how much influence genetics have versus a range of environmental factors, even within families, and many people with IBS have no known prior family history of IBS.
Furthermore, there may be other genes on other chromosomes involved in some cases of IBS as well. As reported by Yuri Saito Loftus, MD, MPH of the Mayo Clinic in the U.S. in 2011, “To date, over a hundred genetic variants in over 60 genes from various pathways have been studied in a number of candidate gene studies with several positive associations reported.” On September 26, 2014, this blog alerted readers to another international collaboration, this one led by the Mayo Clinic, that identified a specific gene mutation thought to account for an estimated 2.2% of cases of IBS, although this cannot be tested clinically in specific patients at this time.
Genetics are among the many areas of IBS research that continue to be actively pursued, including by the GENIEUR.EU network established several years ago by IBS experts to collaborate for this purpose. Its membership has grown over time, now including 25 European countries, Australia, Chile, Israel and the United States, again, often with several participating research centers per country. The continuing work of all of these researchers and many others is a reason for hope that in the future, there will be clearer answers on the origins of irritable bowel syndrome and related disorders.