Gene Discovery in Recessive Structural Brain Disorders through Whole Exome Sequen

描述(申请人提供)：我们将应用完整的外显子组测序，在一大群血缘结合的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，对于促进对大脑发育和功能及其后果(包括癫痫、发育迟缓和运动缺陷)的决定因素的理解具有很大的希望。最近，大脑发育异常也与包括自闭症在内的神经精神障碍有关。由于缺乏大量具有良好特征的队列，对大脑畸形基因的搜索一直受到阻碍。由于结构性脑部疾病在普通人群中并不常见，但在近亲结合的后代中更为普遍，因此这些近亲患者极有可能患有由纯合子突变引起的隐性疾病。这一点已经在许多大脑结构异常中得到证实，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照亮新功能的基因。出于这个原因，我们聚集了世界上最大的结构性脑异常患者之一，他们是血缘关系的产物。其中，我们选择了一个由250个高密度SNP基因分型证实为血缘关系的独立家系组成的高度选择性的组进行外显子组测序。这些病例推测每个病例都代表一种隐性的疾病形式，从而允许有效地应用整个外显子组测序来发现致病突变。推定的疾病突变预计是新的或罕见的纯合子突变，在血缘关系纯合的片段中。在受影响的同胞中发现相同的纯合子突变，而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学证据，证明疾病基因已被识别，进一步的动物模型研究可以证实它们的意义。由于蛋白质编码区只占人类基因组的1%，但却占到了各种孟德尔疾病所有突变的85%，所以人们很早就认识到，外显子的选择性测序应该比测序整个基因组更有效和更经济。此外，在第一次表亲婚姻中受影响的受试者中，只有10%的基因组是血统纯合的，因此寻找疾病突变是有效的，仅限于0.1%的基因组。最后，与检测杂合突变相比，检测纯合子突变明显更容易，更不容易出错，并且需要更低的覆盖深度。基于这些观察，我们已经实现了用于基因发现的整个外显子组测序，并展示了它在这个项目中的有效性。与本RFA的目标一致，我们准备立即对250名精心挑选的患有结构性脑异常的血缘患者进行完整的外显子组重新测序。导致这些异常的基因的发现将允许对大脑发育的基本机械洞察，并有可能为这些和相关的神经精神疾病提供新的治疗方法。 公共卫生相关性：脑部结构异常是癫痫、发育迟缓和智力低下的主要原因。更微妙的形式与其他神经发育障碍有关，包括自闭症。我们建议使用外显子组测序在250个独立家系的高度选择性队列中发现导致脑畸形的基因，这些家系经高密度SNP基因分型证实是近亲。导致这些异常的基因的发现将允许对大脑发育的基本机械洞察，并有可能为这些和相关的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.