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Identical twins, different microbes
The twin puzzle
That puzzle pulled an epidemiologist, someone who studies risk factors across thousands of people at a time, away from joints and bones and into twin research. Clones raised together should turn out the same, and they don't.
What microbes explain
After about ten years of searching, he looked at the gut microbes in twins and found they were different. In 30 years, it is the only thing he has found that really sets identical twins apart.
That difference accounts for why one twin gets cancer while the other doesn't, and why one has an autoimmune disease or depression while the other is happy. It sent the research into nutrition, where much of what had been taught suddenly made sense in a new light.
How do twin studies separate genes from environment?
Identical twins come from one fertilized egg and share essentially all of their DNA, while fraternal twins share about half of the genes that vary between people. If identical pairs resemble each other more than fraternal pairs on a trait, genes are likely contributing to it. The method dates to Francis Galton in the 1870s. The TwinsUK registry at King's College London, founded in 1992, has enrolled about 14,000 twins.
Which gut microbes are inherited?
In a 2014 paper in Cell, Julia Goodrich and colleagues analyzed the gut microbes of 416 twin pairs from TwinsUK. They found that a family of bacteria called Christensenellaceae was among the most heritable and was more common in leaner people. Most other groups varied far more with environment than with genes. In the same study, mice given Christensenellaceae minuta gained less weight.
How do gut microbes affect cancer treatment?
In 2018, the journal Science published three studies, from groups led by Laurence Zitvogel, Jennifer Wargo, and Thomas Gajewski, linking gut bacteria to responses to immunotherapy. Patients whose tumors shrank on drugs that block PD-1 tended to have more diverse gut communities. When researchers transferred stool from responders into mice, the mice's tumors responded better to treatment.
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