Human genetics, the microbiome, and obesity

Editors note: Happy birthday to our intern, Becky Siegert.  She has been helping to bring you the blogs for the past 3 weeks, and we at the AMI deeply appreciate her help with them.  Enjoy the day, Becky!

An article was published last week in Cell out of Ruth Ley's lab at Cornell University that discovered a connection between host genetics and the microbiome.  In doing so, the researchers discovered which aspects of the microbiome were heritable, and how some heritable bacteria in the microbiome are related to obesity.

The researchers obtained stool samples from almost a thousand humans that were twins.  They discovered that twins had more similar microbiomes than non related individuals, and that identical twins had even more similar microbiomes than fraternal twins.  Then, by meticulously analyzing their data sets along with other published twins data they discovered which specific types of bacteria were the most heritable.  They discovered that the bacteria from the family Christensenellaceae were the most heritable.  Interestingly, this family seems to exert great influence over the existence or non existence of other important bacteria in the gut, and it often occurs with methane producing archaea.  Additionally, this family of bacteria appeared to be associated with a low body mass index (BMI), or leanness.  To test the effect of this family of bacteria on obesity the researchers performed a series of microbiome transplants from humans to germ free mice.  In one test, an obese microbiome that was amended with a Christensenellaceae bacteria prior to transplantation resulted in weight loss for the mouse.  In other tests the amount of weight gain in mice mirrored the amount of Christensenellaceae.

This study is important in many ways.  First, it unambiguously connects host genetics to the microbiome.  Second, it connects a specific family of bacteria, Christensenellaceae, to BMI.  This family is heritable and seems to play a large role in shaping the rest of the microbiome.  Altogether this paper adds a new dimension to the microbiome and nutrition.  Many studies associate certain genes with obesity, but perhaps the microbiome is actually responsible.

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