Role of a BHLHB9 polymorphism in the etiology of a developmental disorder

 描述(申请人提供)：患者的高通量基因组筛查为识别罕见的、未诊断的疾病的生物学机制提供了希望，并可能为更常见的疾病类别提供更广泛的洞察力。然而，变异鉴定只是第一步；必须建立变异和表型之间的因果关系，而治疗策略的制定需要对细胞和蛋白质病理学有全面的了解。NIH未诊断疾病计划最近描述了一名男性患者UDP1757的特征，他在15个月时病情恶化，10岁时死亡，新生儿出现运动功能障碍、认知障碍、脑容量减少和周围神经病变。遗传筛查发现位于X染色体上的BHLHB9基因座(C318R)存在半合子单点突变。BHLHB9已被证明可以防止细胞凋亡，促进神经元分化和轴突形成。我们假设C318R导致功能丧失或功能减退的突变，导致神经细胞死亡增加和轴突生长减少，从而导致皮质萎缩和广谱神经功能障碍。这项建议的目的是确定C318R突变在神经元异常死亡、神经元分化和轴突形成减少中的作用。为此，我们建议在体外对小鼠神经干细胞和患者来源的中性分化的iPS细胞中的BHLHB9基因进行修改，以确定细胞病理学。我们还将使用引入Bhlhb9突变的小鼠模型，确定行为表型，并从解剖学上定义中枢神经系统影响。我们预计小鼠将概括UDP1757的临床表型，细胞分析和解剖成像都将产生与我们的假设一致的数据，即BHLHB9 C318R是功能丧失或功能减退的突变。优势是一支在儿科遗传学和罕见疾病、基因工程、转基因小鼠和iPS细胞技术、啮齿动物行为评估以及神经元培养和定量方面具有互补技能的专家团队。此外，该提案还利用了堪萨斯智力和发育障碍研究中心丰富的核心资源。这项探索性/发展性研究资助奖将通过建立对一种未确定的临床表型负责的细胞过程而做出重大贡献，并将为使用本研究中开发的体外和体内工具进行后续研究提供基础，以制定、筛选和测试治疗策略，以改善这种和相关的破坏性发育障碍。

 DESCRIPTION (provided by applicant): High-throughput genome screening of patients provides hope for identifying biological mechanisms in rare, undiagnosed disorders, and may provide broader insight into more common disease categories. However, variant identification is only a first step; a cause-effect relationship between variant and phenotype must be established, and therapeutic strategy formulation requires a thorough understanding of cellular and protein pathologies. The NIH Undiagnosed Disease Program recently characterized a male patient, UDP1757 with neonatal onset of motor dysfunction, cognitive deficiencies, low brain volume, and peripheral neuropathy, worsening at 15 months, and who died at 10 years of age. Genetic screening showed a hemizygous single point mutation in the BHLHB9 locus (C318R) located on the X chromosome. BHLHB9 has been shown to prevent apoptosis and to promote neuronal differentiation and axonogenesis. We hypothesize that C318R results in a loss- or reduction-of-function mutation that results in increased neuronal cell death and reduced axon outgrowth, hence leading to cortical atrophy and broad-spectrum neural dysfunction. The objective of this proposal is to establish a role of the C318R mutation in abnormal neuronal death and reduced neuronal differentiation and axonogenesis. To do so, we propose in vitro assays involving modifications of the BHLHB9 gene in mouse neural stem cells and patient-derived, neutrally differentiated iPS cells in order to define cellular pathologies. We will additionally use mouse models in which Bhlhb9 mutations are introduced, behavioral phenotype determined, and CNS impact defined anatomically. We anticipate that the mouse will recapitulate the clinical phenotype of UDP1757, and that both cell assays and anatomical imaging will yield data consistent with our hypothesis that BHLHB9 C318R is a loss- or reduction-of-function mutation. A strength is a team of experts with complementary skills in pediatric genetics and rare diseases, genetic engineering, transgenic mouse and iPS cell technologies, rodent behavioral assessment, and neuronal culture and quantitation. Additionally, the proposal draws on the rich core resources of the Kansas Intellectual and Developmental Disabilities Research Center. This Exploratory/Developmental Research Grant Award will make significant contributions by establishing cellular processes responsible for an uncharacterized clinical phenotype, and will provide a basis for subsequent studies using the in vitro and in vivo tools developed in this study to formulate, screen and test therapeutic strategies to ameliorate this and related devastating developmental disorders.