Our genetic makeup influences whether we are fat or thin by shaping which types of microbes thrive in our body, according to a study by researchers at King's College London and Cornell University.
By studying pairs of twins at King's Department of Twin Research, researchers identified a specific, little known bacterial family that is highly heritable and more common in individuals with low body weight. This microbe also protected against weight gain when transplanted into mice.
The results, published today in the journal Cell, could pave the way for personalised probiotic therapies that are optimised to reduce the risk of obesity-related diseases based on an individual's genetic make-up.
Previous research has linked both genetic variation and the composition of gut microbes to metabolic disease and obesity. Despite these shared effects, the relationship between human genetic variation and the diversity of gut microbes was presumed to be negligible.
In the study, funded by National Institutes of Health (NIH), researchers sequenced the genes of microbes found in more than 1,000 fecal samples from 416 pairs of twins. The abundances of specific types of microbes were found to be more similar in identical twins, who share 100 per cent of their genes, than in non-identical twins, who share on average only half of the genes that vary between people. These findings demonstrate that genes influence the composition of gut microbes.
The type of bacteria whose abundance was most heavily influenced by host genetics was a recently identified family called 'Christensenellaceae'. Members of this health-promoting bacterial family were more abundant in individuals with a low body weight than in obese individuals. Moreover, mice that were treated with this microbe gained less weight than untreated mice, suggesting that increasing the amounts of this microbe may help to prevent or reduce obesity.
Professor Tim Spector, Head of the Department of Twin Research and Genetic Epidemiology at King's College London, said: 'Our findings show that specific groups of microbes living in our gut could be protective against obesity -- and that their abundance is influenced by our genes. The human microbiome represents an exciting new target for dietary changes and treatments aimed at combating obesity.
'Twins have been incredibly valuable in uncovering these links -- but we now want to promote the use of microbiome testing more widely in the UK through the British Gut Project. This is a crowd-sourcing experiment that allows anyone with an interest in their diet and health to have their personal microbes tested genetically using a simple postal kit and a small donation via our website (www.britishgut.org). We want thousands to join up so we can continue to make major discoveries about the links between our gut and our health.'
Ruth Ley, Associate Professor at Cornell University in the United States, said: 'Up until now, variation in the abundances of gut microbes has been explained by diet, the environment, lifestyle, and health. This is the first study to firmly establish that certain types of gut microbes are heritable -- that their variation across a population is in part due to host genotype variation, not just environmental influences. These results will also help us find new predictors of disease and aid prevention.'

參考譯文：

腸道菌群研究越來越受到重視，已經有研究證據提示腸道細菌是人體不可或缺的一部分。

以往的研究也已發現宿主遺傳變異和腸道菌群組成與代謝性疾病和肥胖之間存在相關性。但是，人類遺傳變異和腸道菌群多樣性之間的關系仍被假定為可忽略不計。

10月6日發表在CELL雜志上的一項研究顯示，一個腸道菌家族具有高度遺傳性，更常見于瘦人。將其移植進小鼠腸道可以防止實驗鼠體重增加。

由NIH資助的這項研究中，來自倫敦大學國王大學和康奈爾大學的研究人員對取自416對雙胞胎的超過1000份糞便樣品中微生物基因進行測序發現，與僅有一半基因相同的異卵雙胞胎比較，具有完全相同基因的同卵雙胞胎腸道某種特定微生物的相對含量更相似。結果表明，遺傳因素對于腸道群種類的影響大于環境因素。

這個相對含量極大程度上受宿主遺傳影響的腸道益生菌家族被命名為“Christensenellaceae”。這個益生菌家族成員菌被發現在瘦人腸道豐度高于肥胖人群。而且，接受這類細菌移植的小鼠不容易長胖，說明增加腸道中這類細菌的量可能有助于防止或減輕肥胖。

本研究的意義在于： 1）第一次確立了宿主遺傳因素決定腸道細菌種類的相對含量； 2）證明多種可遺傳菌種可共存共現； 3）最受遺傳影響的Christensenellaceae益生菌與宿主體重指數相關； 4）預示著將來可以通過“糞便移植”幫助防治肥胖和肥胖相關疾病。