A diverse set of chronic diseases such as metabolic and autoimmune disorders may be caused by the bacteria in your gut microbiome. Factors like diet, antibiotics, and lifestyle choices play a major role in why the microbial composition varies from person to person; however, specific gene variants and mutations are also related to a higher risk for developing disease. Researchers now believe the microbiome influences your genes, potentially triggering disease.
Researchers at the University of Colorado Denver chose specific genes with a compelling link to disease and the hosts' microbiome, including variants of the NOD2 gene. They then compared the microbiomes of people with known mutations and higher risk of disease with those of "healthy" microbiomes without mutations.
The gut microbiomes of the mutation carriers were found to have an increased risk of IBD, as well as a dysbiotic gut microbiome.
Comparing twins is thought to be a much more definitive way of observing the effects of genetic variation because 100 percent of their genes are shared while fraternal twins only share 50 percent. In addition, twins are typically raised in similar environments, thus their gut microbiomes should, in theory, be alike.
If the microbiomes of the identical twins are more alike than those of the fraternal twins, we can hypothesize that genes have probably influenced this difference. If microbial variation within identical and fraternal twins is about the same, a shared genome has likely had no additional effect.
Early twin studies did not detect any significant differences in the microbiomes of identical twins. But recent studies have compared nearly 500 twin pairs, a sample size large enough to show an obvious genetic effect on the relative abundance of a specific set of bacteria. In addition, lean twins were shown to have more genetic bacteria, or bacteria influenced by genetics, than the obese twins.
One microbe, Christensenella minuta, was shown to definitively affect the host phenotype. Germ-free mice, which live in sterile environments and are underweight, were given a fecal transplant from a human. Within days of receiving the transplant, the mice gained a significant amount of weight. Researchers believe that the bacteria found within the transplant aided the mice in digestion and metabolism. Mice were found to be thinner when the human samples lacked C. minuta, which was often the case for transplants from obese donors. These results reveal that C. minuta is capable of moderating adiposity in mice.
The research indicates that our genes can affect the gut microbiome’s composition and ultimately affect our phenotypes. Future studies hope to find specific genes that might be implicated and how influencing the microbiome might minimize the chances of developing chronic disease, suggesting potential novel treatments for obesity and other metabolic disorders.
Ley, Ruth E. "Genes and Microbes Influence One Another, Scientists Find." Scientific American. March 03, 2015. http://www.scientificamerican.com/article/genes-and-microbes-influence-one-another-scientists-find/.