Impact of Genetic Variation on Folate Metabolsim: Etiology of Neural Tube Defects

描述（由申请人提供）：神经管缺陷（NTDs）是一种常见的、昂贵的、致命的人类先天性异常，其病因在很大程度上仍然未知。关于被忽视热带病病因的最有希望的线索之一是，在怀孕早期使用含有叶酸的维生素的妇女患被忽视热带病的怀孕风险要低得多。然而，叶酸有助于降低这些风险的潜在机制尚不清楚。最普遍的假设是叶酸摄入通过补偿个体遗传易感性来预防ntd，尽管通过关联研究明确确定遗传决定因素已被证明是难以捉摸的。我们提出的进一步确定神经管缺陷和叶酸预防治疗背后的分子遗传机制的方法植根于一项初步研究的结果，该研究旨在确定损害功能的维生素依赖酶的非同义替代，但可以通过提高维生素浓度来增强。这个试点已经证明，深度测序揭示了大量的低频，非同义的叶酸途径基因变异（频率<=1%），迄今为止被忽视。此外，使用基于酿酒酵母互补的强大检测平台，我们已经证明了大约一半的这些低频变异影响酶功能，并鉴定了新的叶酸补救等位基因。我们假设叶酸代谢的遗传易感性可能是ntd的病因，这些易感性可能由低频和常见变异以及它们之间可能的协同作用赋予。为了验证这一假设，我们将对来自250名ntd患儿和250名对照人群的19个叶酸代谢基因的编码区域进行重新排序，我们也有关于母亲营养摄入的信息。我们将测试所有酶变体的功能影响和叶酸修复，并将功能研究与临床表型和营养数据相关联。我们希望能更好地定义ntd的因果关系，了解叶酸补充剂的治疗作用，并确定额外补充叶酸是否可以预防。我们汇集了独一无二的科学专家来执行这项研究计划。

DESCRIPTION (provided by applicant): Neural tube defects (NTDs) are common, costly, and deadly human congenital anomalies whose etiologies remain largely unknown. One of the most promising clues to the causes of NTDs is that women who use vitamins containing folic acid in early pregnancy are at much lower risk for NTD-affected pregnancies. However, the underlying mechanisms by which folic acid contributes to these reduced risks are unknown. The most commonly held hypothesis is that folate intake prevents NTDs by compensating for individual genetic susceptibilities, although clear identification of genetic determinants through association studies has proven elusive. The approach we propose to further define the molecular genetic mechanisms behind neural tube defects and folate-prevention therapy is rooted in the results of a pilot study to identify nonsynonymous substitutions in vitamin-dependent enzymes that impair function, yet are augmentable by elevated vitamin concentration. This pilot has demonstrated that deep sequencing reveals a substantial amount of low frequency, nonsynonymous variation in folate pathway genes (frequencies <=1%) that has gone unnoticed thus far. Furthermore, using a robust assay platform based on complementation in S. cerevisiae, we have demonstrated that approximately one-half of these low frequency variants affect enzyme function and have identified novel folate-remedial alleles. We hypothesize that genetic susceptibilities in folate metabolism can be etiological for NTDs and that these susceptibilities can be conferred by both low-frequency and common variants and by the possible synergy between these. To test this hypothesis, we will resequence the coding regions in 19 folate metabolic genes from a population of 250 NTD-affected infants and 250 controls, for which we also have information on maternal nutritional intake. We will test all enzyme variants for functional impact and folate remediation, and correlate functional studies with clinical phenotype and nutritional data. We hope to better define the causality of NTDs, understand the remedial role of folate supplementation, and determine whether additional folate supplementation may be preventative. We have assembled a unique combination of scientific expertise to execute this research plan. Relevance: This proposal should reveal the causes of a common form of birth defect known as neural tube defects. Ultimately, this research may lead to better diagnostic and preventive strategies.