Gene Discovery in Recessive Structural Brain Disorders through Whole Exome Sequen

描述（由申请人提供）：我们将应用全外显子组测序在大量近亲结合患者中发现导致结构性脑疾病的突变。全面发现导致大脑畸形的突变，对促进对大脑发育和功能的决定因素及其后果（包括癫痫、发育迟缓和运动缺陷）的理解大有希望。最近，大脑发育异常也被认为与神经精神疾病有关，包括自闭症。由于缺乏具有良好特征的大样本，对脑畸形基因的研究一直受到阻碍。由于结构性脑疾病在一般人群中并不常见，但在近亲结合的后代中更为普遍，这些近亲患者极有可能患有由纯合突变引起的隐性疾病。这已经被证实为许多大脑结构异常，这些异常已经确定了神经元引导分子及其受体，以及其他在大脑发育中阐明了新功能的基因。出于这个原因，我们收集了世界上最大的脑结构异常患者的集合，这些患者都是近亲结合的产物。其中，我们选择了一个高度选择性的250个独立家族，通过高密度SNP基因分型证实是近亲，进行外显子组测序。这些病例假定每一个都代表一种隐性形式的疾病，允许有效地应用全外显子组测序来发现致病突变。假定的疾病突变预计是在近亲血统纯合的片段内的新颖或罕见的纯合突变。在受影响的兄弟姐妹中发现相同的纯合突变和在其他队列成员中发现相同基因的独立突变将提供强有力的遗传证据，表明疾病位点已经确定，进一步的动物模型研究可以证实其意义。由于蛋白质编码区仅占人类基因组的约1%，但在各种孟德尔疾病中占所有突变的约85%，因此长期以来人们一直认识到外显子的选择性测序应该比全基因组测序更有效和更经济。此外，在来自近亲婚姻的受影响对象中，只有约10%的基因组是纯合的，因此对疾病突变的搜索是有效的，仅限于0.1%的基因组。最后，纯合突变的检测比杂合突变的检测明显更容易，更不容易出错，并且需要更低的覆盖深度。基于这些观察结果，我们实施了基因发现的全外显子组测序，并展示了其在本项目中的实用性。与本RFA的目标一致，我们准备立即对250例精心挑选的同源性脑结构异常患者进行全外显子组重测序。发现导致这些异常的基因将使我们能够深入了解大脑发育的基本机制，并有可能为这些和相关神经精神疾病提供新的治疗方法。

DESCRIPTION (provided by applicant): We will apply whole exome sequencing to discover mutations causing structural brain disease in a large cohort of patients from consanguineous union. Comprehensive discovery of mutations that cause brain malformations holds great promise for advancing understanding of determinants of brain development and function and its consequences including epilepsy, developmental delay, and motor deficits. Recently, abnormalities in cerebral development have also been linked to neuropsychiatric disorders, including autism. The search for brain malformation genes has been hampered by the lack of large well-characterized cohorts. Because structural brain disorders are uncommon in the general population but much more prevalent among the offspring of consanguineous union, these consanguineous patients are highly likely to have recessive disease caused by homozygous mutations. This has been confirmed for a number of structural brain abnormalities, which have identified neuronal guidance molecules and their receptors, as well as other genes that have illuminated novel functions in brain development. For this reason, we have assembled one of world's largest collections of patients with structural brain abnormalities who are products of consanguineous union. Among these, we chose a highly selective group of 250 independent families, confirmed to be consanguineous by high density SNP genotyping, for exome sequencing. These cases presumptively each represent a recessive form of disease, allowing efficient application of whole exome sequencing to discover causative mutations. The presumptive disease mutations are expected to be novel or rare homozygous mutations within segments homozygous by consanguineous descent. The finding of the identical homozygous mutation in affected sibs and independent mutations in the same gene in other cohort members will provide strong genetic evidence that disease loci have been identified, and further studies in animal models can confirm their significance. Because protein coding regions represent only ~1% of the human genome but account for ~85% of all mutations in diverse Mendelian disorders, it has long been recognized that selective sequencing of exons should be more efficient and cost effective than sequencing whole genomes. Moreover, in affected subjects from 1st cousin marriages, only ~10% of the genome is homozygous by descent, so the search for disease mutations is efficient, confined to 0.1% of the genome. Finally, detection of homozygous mutations is markedly easier, less error prone and requires lower depth of coverage than detection of heterozygous mutations. Based on these observations, we have implemented whole exome sequencing for gene discovery and shown its utility for this project. Consistent with the goals of this RFA, we are ready to proceed immediately with whole exome re-sequencing of 250 carefully selected consanguineous patients with structural brain abnormalities. Discovery of genes causing these abnormalities will allow fundamental mechanistic insights into brain development and potentially allow new therapeutic approaches to these and related neuropsychiatric disorders. PUBLIC HEALTH RELEVANCE: Structural brain abnormalities are a major cause of epilepsy, developmental delay and mental retardation. More subtle forms are associated with other neurodevelopmental disorders, including autism. We propose to use exomic sequencing to discover genes that cause brain malformations in a highly selective cohort of 250 independent families, confirmed to be consanguineous by high density SNP genotyping. Discovery of genes causing these abnormalities will allow fundamental mechanistic insights into brain development and potentially allow new therapeutic approaches to these and related neuropsychiatric disorders.