华裔科学家首次发现与孕期\/早产相关基因位点

【BioArt按】 《新英格兰医学杂志》2017年9月21日发表论著《妊娠时长和自发性早产的遗传关联》（Genetic Associations with Gestational Duration and Spontaneous Preterm Birth），《NEJM医学前沿》特邀该文 第一作者张戈教授及通讯作者Louis J. Muglia教授 撰写述评，解读此项GWAS研究，并在官网及 微信公众号发表该文的中译全文。经“ NEJM医学前沿 ”授权，BioArt全文转载此文，以飨读者。

早产是新生儿和5岁以下儿童死亡的主要原因。此外，早产与许多长期的不良健康状况有着密切的关联，如肥胖、心血管代谢紊乱和很多神经精神疾病。尽管有着重要的健康意义，科学家也经过了多年努力，由于缺乏对人类出生时间控制机制的了解，预防早产的进展十分有限。

人类的妊娠是独一无二的——每个物种都有独特的机制来控制妊娠时间的长短；关于控制人类妊娠期长短的机制，动物模型仅能提供有限的信息。此外，简单的孟德尔（单基因遗传）疾病也未能提示早产的发病机制。由于这些原因，人类妊娠期长短的遗传控制仍然是一个未解之谜。

妊娠时间长短也是一种特别的表型，它受两个基因组（母体和胎儿）控制，也受到其他基于非DNA序列的跨代效应的影响。 对这些效应的研究，不仅可以揭示潜在的遗传变异的作用机制，还有助于了解不同的进化机制（如母胎冲突、共同适应、亲代效应）在人类怀孕过程中的作用。

在这项研究中，通过一个大规模的基因组关联研究（GWAS），我们第一次发现并重复了6个基因位点与妊娠期的长短或与早产的风险相关。

妊娠时间的长短是一个复杂的性状，受到多种遗传因素和环境因素的影响。检测单个基因变异的关联需要大量样本。先前关于自发早产的研究应用约1000例病例/对照，但未能发现任何可以重复的关联位点。

为了增加研究的统计功效，我们利用了来自23andMe研究的约44000名女性参与者的数据。她们回答了关于既往怀孕的问题，并同意将她们的基因组信息用于科学分析。这一庞大的发现数据为我们的基因组发现奠定了基础。

在约8000例从三个北欧国家（包括丹麦、挪威及芬兰）收集到的样本中，我们重复了从发现样本（23andMe样本）中所找到的相关基因位点。与23andMe的数据相比，这些用于重复检测的样本有着更准确的表型数据和孕周信息。

通过这一双阶段的全基因组关联研究，我们发现母体基因组中6个基因组位点（ EBF1、 EEFSEC、AGTR2、WNT4、ADCY5 和 RAP2C ）与妊娠的时间长短及早产相关。这些基因位点在子宫发育、母体营养和血管控制方面的功能作用支持了它们在控制分娩时间中的作用。例如， WNT4 位点表明子宫内层细胞（即子宫内膜）在怀孕期间有较大作用。另一个确定的基因区域（ EEFSEC ）则提示缺乏硒——一种常见于某些坚果、绿色蔬菜、肝脏和其他肉类中的膳食矿物质——可能会影响早产的风险。我们对这些基因位点的功能分析正在进行之中，以期进一步了解这些遗传关联背后的分子机制。

应该注意的是，如同其他大多数人类复杂性状，这些所发现的关联位点只有很小的作用（这6个已识别的基因位点只能共同解释 < 1%的妊娠长短或早产风险的表型变异）。因此， 这些位点并不具备预测早产的临床诊断价值。我们研究结果的主要价值体现在这些所识别的基因位点所蕴涵的新的生物学知识。

本研究所确定的六个基因位点为未来的研究奠定了起点，很多下一步的研究已在进行之中。

首先，这项研究表明，在大样本中进行全基因组分析，从而识别与妊娠期长短和早产风险相关的基因变异，是一种可行的方法。以此为基础，我们计划在更多的样本中扩大在基因组中的发现。我们将发现并重复更多与妊娠期长短和早产相关联的基因位点。这些新发现的位点与已经识别的位点结合在一起，将为人类妊娠和出生时间控制提供更多的知识。

由于妊娠期长短受母体和胎儿基因组的影响，我们将在婴儿样本中检测遗传关联，以探索潜在的胎儿基因组关联。我们设计了一种新的统计方法，可以在母亲/婴儿对中同时检测母婴的遗传关联。

早产率有着明显的种族/民族差异，例如，与欧洲或亚洲裔的个体相比，非洲裔的个体有较短妊娠期和较高的早产风险。这一种族/民族差异的一部分可能是由于不同种族/民族之间的遗传异质性所导致。我们计划将发现扩展到亚洲和非洲人群。

除了上述的遗传分析，我们还将进行功能研究，以阐明这些基因位点的遗传变异的分子机制。这些将包括辨识具备功能的遗传变异，以及在生物学相关的组织/细胞中应用合适的方法，研究这些遗传变异对转录因子（TF）结合及基因表达的调控作用。我们还将使用动物模型和基因编辑技术来证实它们的功能效应。

其中一个基因关联位点（ EEFSEC ）暗示了硒在怀孕中可能的作用。但是目前还不清楚是否因为没有摄入足够多的富含硒的食物，或者由于身体未能适当地吸收这一矿物质，而使一些女性面临更高的早产风险。我们计划在全世界收集样本，测量女性怀孕期间的硒水平，并调查这些水平是否与早产风险有关。

总而言之，我们的研究表明， 对大量女性及她们后代的基因组信息和出生时间数据的集成分析将有助于识别与妊娠期长短相关的基因位点，这些基因位点的发现将提供重要的生物知识并提示潜在的预防和治疗措施 。

Preterm birth is the single leading cause of mortality for neonates and children less than 5 years of age. In addition, preterm birth is associated with many long-term adverse health outcomes, such as obesity, cardiometabolic disorders, and neuropsychiatric conditions. Despite the health significance and years of research efforts, less progress has been made in the prevention of preterm birth largely due to the lack of understanding of the mechanisms of human birth-timing control.

Human gestation is unique – each species has a unique mechanism for controlling gestational length and animal models provide limited information about the mechanisms behind the control of human gestational length. In addition, simple Mendelian disorder has not shed light on the pathogenesis of preterm birth. For these reasons, the genetic control of human gestational length is still an unsolved mystery.

Gestational length is a unique phenotype, in a sense that it is defined by two genomes (maternal as well as fetal) and also influenced by non-DNA sequence-based transgenerational effect. The fine dissection of these effects will not only reveal the mode-of-action of the underlying genetic variants, but also help the understanding of the different evolutionary forces (e.g. maternal-fetal conflict, co-adaptation, parental effect) in human pregnancy.

In this study, we performed a large-scale genomewide association study and we discovered and replicated, for the first time, six genetic loci in the maternal genome that are associated with length of gestation or risk to preterm birth.

The length of gestation is a complex trait – influenced by multiple genetic and environmental factors. The detection of individual genetic variant association requires large sample size. Previous studies of spontaneous preterm birth approximately with 1000 cases/controls failed to identify any replicated association signal.

To increase the study power, we utilized the data from more than 44,000 women who were research participants of 23andMe. These women also answered questions about their past pregnancies and agreed that their genetic information could be analyzed for science. This large discovery data set built the foundation of our genome-wide discoveries.

We replicated the findings identified from the discovery samples (23andMe samples) in ~8,000 samples collected from three Nordic countries, including Denmark, Norway and Finland. Compared with the 23andMe discovery data set, the phenotype data and the gestational length information in these replication samples were more accurately measured.

Through this two-stage genome-wide association study, we identified six genomic loci ( EBF1, EEFSEC, AGTR2, WNT4, ADCY5 and RAP2C ) in the maternal genome robustly associated with gestational length and preterm birth. The functional roles of these loci in uterine development, maternal nutrition, and vascular control support their mechanistic involvement in birth timing control. For example, the association at the WNT4 loci suggests that cells within the lining of the uterus (i.e. endometrium) play a larger-than-expected role in the length of pregnancy. Another identified gene region ( EEFSEC ) raises important questions about how a lack of selenium — a common dietary mineral found in some nuts, certain green vegetables, liver and other meats — might affect preterm birth risk. Functional analyses of these genomic loci were underway to future understand the molecular mechanisms underlying the genetic associations.

It should be noted that, like most other human complex traits, the effect sizes of the identified associations are uniformly small (in combination, the six identified loci only explain <1% of phenotypic variation in length of gestation or preterm birth risk), and therefore, these identified loci have no clinical diagnostic value in prediction of preterm birth. The major value of our findings lays in the novel biological insights implicated by these identified gene loci.

The six gene areas identified by the project serve as the starting point for future research, some of which has already begun.

First, this study confirmed that genome-wide analysis in large samples is a feasible approach to identify genetic variants associated with gestational duration and preterm birth risk. With this foundation, we plan to expand genomic discovery in more samples. We anticipate discovering and replicating more genomic loci associated with gestational length and preterm birth. Together with the six already identified loci, these newly discovered loci will provide additional insights into human gestation and birth timing control.

Since length of gestation is influenced by both maternal and fetal genomes, we will test for genetic associations in infant samples to explore potential fetal genomic associations. We designed a statistical approach to jointly test maternal and fetal genetic associations simultaneously in mother/infant pairs.

There are significant racial/ethnic disparity in rate of preterm birth, e.g. individuals of African ancestry tend to have shorter gestational length and higher risk of preterm birth compared with individuals of European or Asian ancestry. Part of this racial/ethnic disparity might be attributable to genetic heterogeneities between different racial/ethnic groups. We plan to extend our findings to Asian and African populations.

In addition to the aforementioned genetic analyses, we will conduct functional studies to elucidate the molecular mechanisms of the genetic variants underlying the identified genetic loci. These will include prioritize putative causal variants and interrogation of their regulatory effects on transcription factor (TF) binding and gene expression by appropriate functional assays in biologically relevant tissue/cells. We will also use animal model and gene editing technology to confirm their functional effects.

One gene association ( EEFSEC ) points to the possible role of selenium in pregnancy. However, it remains unclear whether some women face higher risk of preterm birth simply because they do not eat enough selenium-rich food, or whether their bodies do not properly absorb the mineral. We plan to measure selenium levels during pregnancy in women throughout the world and investigate whether those levels are associated with risk for preterm birth.

To summarize, our study suggests that integration of genomic information from a large sample of women and their offspring, with birth timing data, will allow identification genomic loci associated with length of gestation and these genomic findings will provide important biological knowledge and potentially new options for preventative and therapeutic measures.

本文由《NEJM医学前沿》编辑部负责翻译及编写，内容以英文原版为准，中译全文由马萨诸塞州医学会NEJM集团独家授权。欢迎转发至朋友圈，如需转载，请联系[email protected]。未经授权的翻译是侵权行为，版权方将保留追究法律责任的权利。

Copyright ©2017 Jiahui Medical Research and Education Group. All Rights Reserved