通过基因组测序获取人类自身具有基因敲除效应的突变，并用于新药研发。

最近几十年来，生物学家多通过在小鼠或其它实验动物身上失活某个基因，来观察这个基因的功能。现在，这种基因敲除研究功能的模式又有了新的更理想的物种材料：人类自身。

这种方法可不是在实验室中通过基因工程制备基因突变的人，研究人员通过扫描成千上万的人基因组序列，来找寻自然发生的突变所致特定基因的失活。通过观察这些突变如何影响健康，研究者希望获得疾病的生物学根源并找到新的治疗方式。

上周，在加州圣地亚哥美国人类遗传学会（American Society of Human Genetics）会议的分会上，遗传学家们讨论了几个这种大规模（测序数据）的效应。来自波士顿马省总医院（Massachusetts General Hospital）的基因组学家Daniel MacArthur说，我们现在所有认知都是基于小鼠和大鼠的，而不是基于人。他的研究组通过扫描超过9万人的基因组蛋白编码区，已经确定了大约15万自然发生的敲除基因。“现在我们发现了拥有某特定失活的基因或者特定修饰的基因，我们可以直接利用他们来检验我们的假设。”

平均每个人都携带不少的基因突变，这些突变导致至少1/200基因出现单拷贝失活，导致大约1/20基因出现双拷贝失活。然而，要得到任何一个基因的敲除突变却很难，因此需要大人口规模来研究其效应。这类功能缺失突变在特定疾病中，例如囊肿性纤维化，被广泛采用。多数突变对健康并无损害，一些突变甚至对携带者有益。“（很多突变不导致疾病，因而）我们不会在临床上看到，但是他们在生物学上依旧很有价值”，MacArthur说。MacArthur及其研究组将关注的焦点放在基因组数据上，他们现在也开始通过患者—健康记录来确定哪些相对微弱突变导致的效应。在一项有超过36000芬兰人参与的研究中(发表于PLoS Genet. 10, e1004494; 2014)，MacArthur的团队发现缺失LPA基因可能有心脏保护作用，另一种敲除突变，在芬兰人中有2.4%的人为该突变的单拷贝携带者，这种突变如果以双拷贝形式出现则容易引起流产。

来自休斯敦德克萨斯健康科学中心大学（University of Texas Health Science Center）的Bing Yu在会上说，他的团队将1300多人的基因敲除突变数据与血液中300多分子数据进行了比较，发现基因SLCO1B1上的突变与高脂肪酸有关，高脂肪酸是心衰的风险因子。英国Hinxton之Wellcome Trust Sanger研究所的一个研究组报道：在小鼠中失活具有致死效应的43个基因，在人体这些基因失活时人却看上去很健康，并不呈现致死效应。

宣传海报

循此方式可以揭开人类成千未知功能基因的作用。并可能通过确认具有保护性（让人免受疾病困扰）的基因或生物通路来辅助药物研发。

人类基因敲除效应的宣传海报（poster child）是一类新型、可阻止PCSK9基因的药物(Nature 496, 152–155; 2013)。PCSK9基因于本世纪早期在高胆固醇的法国人家族中被发现。研究人员很快发现：在PCSK9单拷贝失活这样一种罕见突变的人群中，胆固醇含量低，少有心脏病发生。首个阻止PCSK9的药物将在明年问世，并预计将在未来五年中产生250亿美元的销量收入。

加利福尼亚La Jolla 的Scripps转化科学研究所（Scripps Translational Science Institute）领导人Eric Topol说：“将来会有成百，甚至成千个像PCSK9基因样的故事出现”。药物可以模拟功能缺失型突变。耶鲁大学的生物信息学家Mark Gerstein则认为人类基因突变在研发对抗衰老性疾病上尤其重要。“你可以想象状况，某个基因在你25岁的时候对你有益，而当你75岁的时候，它或许对你有害了。”

“通过这些基因敲除数据，你可以很容易的理解为什么现在越来越多的人通过基因组测序来寻求自己所患疾病的解决方案了吧。” 伦敦肿瘤研究所的医学遗传学家Nazneen Rahman说。Rahman在会上展示了她的团队对1000个英国人基因敲除突变的分析结果，这些信息确切无疑的表明发生在人类的基因突变比我们先前想象的多许多。

当利用人类基因组测序确认某神秘疾病的原因时，任何敲除型突变都是可疑原因。拥有这些突变的完整清单以及它们的健康效应（或缺失效应）将有助于确定疾病的真是原因，Rahman说。

MacArthur团队上周刚释放了约63000人的敲除及其它信息，已经有人在利用这些数据了。“当我看到这些数据时，我做的第一件事就是查看我所关注的严重疾病有关基因，看是否有什么人在这数据库中，我还真发现了他们”，休斯敦Baylor医学院的医学遗传学家John Belmont说。（在这批人中）他发现了11个人携带有马凡氏综合征相关基因突变，这种疾病累及结缔组织，如果不予处理，可能引起突发性心力衰竭。

这些人可能属于潜伏的病例，他们可能具有保护性、防止发病的机制或是存在测序错误。Belmont说：“携带致病的突变基因而不发病，这太迷人了，我们将好好关注它，这或许预示着马凡氏综合征的新治疗方式。

链接：http://www.nature.com/news/geneticists-tap-human-knockouts-1.16239

文题：Geneticists tap human knockouts

Sequenced genomes reveal mutations that disable single genes and can point to new drugs.

Ewen Callaway

For decades, biologists have studied gene function by inactivating the gene in question in mice and other lab animals, and then observing how it affects the organism. Now researchers studying such gene ‘knockouts’ have another, ideal model at their disposal: humans.

The approach does not involve genetically engineering mutant people in the lab, as is done in mice. Instead, researchers scan the genomes of thousands or millions of people, looking for naturally occurring mutations that inactivate a particular gene. By observing how these mutations affect health, researchers hope to gain insight into basic biology and to unearth new disease treatments.

Geneticists discussed several such large-scale efforts during a packed session at the American Society of Human Genetics meeting in San Diego, California, last week. “So much of what we know is based on mice and rats, and not humans,” says Daniel MacArthur, a genomicist at Massachusetts General Hospital in Boston, whose team identified around 150,000 naturally knocked-out genes by trawling the protein-coding portion of the genome, or exome, in more than 90,000 people. “Now we can find people who actually have a particular gene inactivated or somehow modified, and that allows us to test hypotheses directly.”

On average, every person carries mutations that inactivate at least one copy of 200 or so genes and both copies of around 20 genes. However, knockout mutations in any particular gene are rare, so very large populations are needed to study their effects. These ‘loss of function’ mutations have long been implicated in certain debilitating diseases, such as cystic fibrosis. Most, however, seem to be harmless — and some are even beneficial to the persons carrying them. “These are people we’re not going to find in a clinic, but they’re still really informative in biology,” says MacArthur.

His group and others had been focusing on genome data, but they are now also starting to mine patient-health records to determine the — sometimes subtle — effects of the mutations. In a study of more than 36,000 Finnish people, published in July (E. T. Lim et al. PLoS Genet. 10, e1004494; 2014), MacArthur and his team discovered that people lacking a gene called LPA might be protected from heart disease, and that another knockout mutation, carried in one copy of a gene by up to 2.4% of Finns, may cause fetuses to miscarry if it is present in both copies.

Bing Yu of the University of Texas Health Science Center in Houston told the meeting how he and his collaborators had compared knockout mutations found in more than 1,300 people with measurements of around 300 molecules in their blood. The team found that mutations in one gene, called SLCO1B1, were linked to high levels of fatty acids, a known risk factor for heart failure. And a team from the Wellcome Trust Sanger Institute in Hinxton, UK, reported that 43 genes whose inactivation is lethal to mice were found to be inactivated in humans who are alive and apparently well.

Poster child

Following up on such insights will help researchers to unpick the functions of the thousands of human genes about which little or nothing is known, say MacArthur and others. It might even aid drug discovery by identifying genes or biological pathways that could protect against disease.

The poster child for human-knockout efforts is a new class of drugs that block a gene known as PCSK9 (see Nature 496, 152–155; 2013). The gene was discovered in French families with extremely high cholesterol levels in the early 2000s. But researchers soon found that people with rare mutations that inactivate one copy of PCSK9 have low cholesterol and rarely develop heart disease. The first PCSK9-blocking drugs should hit pharmacies next year, with manufacturers jostling for a share of a market that could reach US$25 billion in five years.

 “I think there are hundreds more stories like PCSK9 out there, maybe even thousands,” in which a drug can mimic an advantageous loss-of-function mutation, says Eric Topol, director of the Scripps Translational Science Institute in La Jolla, California. Mark Gerstein, a bio-informatician at Yale University in New Haven, Connecticut, predicts that human knockouts will be especially useful for identifying drugs that treat diseases of ageing. “You could imagine there’s a gene that is beneficial to you as a 25-year-old, but the thing is not doing a good job for you when you’re 75.”

The human-knockout data presented last week will also make it easier to interpret the growing number of genomes being sequenced from people seeking treatment, says Nazneen Rahman, a medical geneticist at the Institute for Cancer Research in London. Rahman told the meeting about her team’s analysis of knockout mutations in 1,000 British people. “The take-home message is that these types of mutations occur much more commonly than people thought,” she says.

When a person’s genome is sequenced to identify the cause of a mysterious illness, any knockout mutations that turn up are obvious suspects. Having a complete list of such mutations and their health effects (or lack thereof) should help to identify the true causes of a disease, Rahman says.

To that end, MacArthur’s team last week released knockout and other data from some 63,000 people — and others are already making use of this trove. “One of the first things I did when they released the data was to look at all my favourite genes for very severe diseases, to see if there are people in those databases — and there are,” says John Belmont, a medical geneticist at Baylor College of Medicine in Houston. He found 11 people with mutations associated with Marfan syndrome, a disorder that affects connective tissue and that can cause sudden heart failure if left untreated.

However, these people may be silent cases, they might somehow be protected against the disease or their genomes might have been sequenced incorrectly. People who carry disease-causing mutations but don’t get sick are especially intriguing, he says. “We should pay attention to them,” Belmont says. “They may hold a key for new treatments.”

上文由群晓科苑翻译整理，科学推广，服务民众。他人或机构如需使用，请提供该原始链接地址。

北京群晓科苑生物技术有限公司主要经营生物医药领域的试剂、耗材和仪器。群晓生物致力于为用户提供优质的材料、技术和实验整体性解决方案，完美配合用户的科研创意和灵感。群晓生物立志把一流的产品、专业的技术和完善的售后服务献给广大用户。

北京群晓科苑生物技术有限公司

www.qbioscience.com

www.qbiotec.com

Tel: 010-84504282/64880108

qbioscience@126.com