Molecular Genetics of BBS

数以千计的患者外显体和基因组的产生，在加速诊断的同时，也突显了 以前认为的“简单”特征的复杂性。据报道，现在有许多患者患有 多个基因中的有害等位基因。在某些情况下，表型反映了两种疾病的混合；在另一些情况下，它 是基因相互作用的产物。此外，最近基于外显子组或小组的组的重新测序 已知的导致一系列显性或隐性疾病的基因开始报告了一种罕见的 患者中的变异，突出了突变负担的概念。Bardet-Biedl综合征(BBS) 纤毛病，一直是研究这些现象和开始了解 这样的等位基因对非外显性和可变表现力有影响。这是因为：(A)大多数隐性的 目前已知BBS的负担，约80%的BBS患者在22个基因上存在隐性突变；(B)大多数 BBS蛋白是纤毛结构/功能所必需的，并组装成特定的复合体；以及(C)我们和 其他人已经开发了定量的体外和体内工具来评估纤毛的总功能输出； 以确定变异的影响；并测量遗传交互作用。本次更新重点关注三个主题。 首先，我们将利用前几个周期中广泛的遗传和功能数据，建立一个全面的 生物模块中的突变分布图。通过对两个独立论坛的严谨分析 在患者队列中，我们观察到已知BBS基因的罕见变异增加了2.5倍 隐性驱动程序。这种变异不是随机分布的，而是暗示了突变之间的相互作用 映射到不同的大分子复合体。使用已建立的BBS的老鼠模型，我们将询问这些 相互作用可能会增强或加剧离散的BBS内表型。第二，我们将利用 最近在人类和小鼠纤毛疾病模型中观察到顺式和反式作用的作用 遗传修饰物。关注TTC21B/IFT139，一种导致因果和修饰突变的基因 在整个睫毛病疾病谱中，我们将检验该基因座突变对 通过利用斑马鱼模型中的大量数据并测试 老鼠体内的范例。同时，使用计算和生物工具的组合，会问 该基因座离散点突变可以解释致病等位基因的可变活性 P.P209L，人类中的一种低晶型，但在老鼠中为零等位基因。最后，根据最近的观察， 来源于全基因组遗传抑制筛选，蛋白酶体的增强改善了BBS 在体外和体内，我们将使用我们最近开发的蛋白酶体传感器筛选范例来执行 小分子筛选新的治疗线索。这些研究将使我们全面了解 一种遗传异质性、表型可变的样本疾病的体系结构，同时， 允许理性地发现新的治疗范例。

The generation of 1000s of patient exomes and genomes, while accelerating diagnoses, has also highlighted the complexity of previously-considered “simple” traits. Numerous examples are now reported of patients with deleterious alleles in multiple genes. In some, the phenotype reflects an amalgam of two disorders; in others, it is the product of genetic interactions. Moreover, recent exome- or panel-based resequencing of groups of genes known to cause a host of dominant or recessive disorders are beginning to report an enrichment of rare variants in patients, highlighting the concept of mutational burden. Bardet-Biedl syndrome (BBS), a founding ciliopathy, has been a model for studying these phenomena and for beginning to understand the contribution of such alleles to non-penetrance and variable expressivity. This is because: (a) the majority of the recessive burden in BBS is now known, with ~80% of BBS patients harboring recessive mutations in 22 genes; (b) most BBS proteins are necessary for cilia structure/function and assemble into defined complexes; and (c) we and others have developed quantitative in vitro and in vivo tools to assess the total functional output of the cilium; to establish the effect of variants; and to measure genetic interactions. This Renewal focuses on three themes. First, we will capitalize on extensive genetic and functional data from previous cycles to build a comprehensive map of mutational distribution in a biological module. Through the rigorous analysis of two independent BBS patient cohorts, we have observed a 2.5-fold increase of rare variants in known BBS genes beyond the recessive driver. This variation is not distributed randomly but intimates an interaction between mutations that map to different macromolecular complexes. Using established, mouse models of BBS, we will ask how these interactions might potentiate or exacerbate discrete BBS endophenotypes. Second, we will take advantage of recent observations in humans and mouse models of ciliopathies to dissect the role of cis- and -trans acting genetic modifiers. Focusing on TTC21B/IFT139, a gene that contributes causal and modifying mutations across the ciliopathy disease spectrum, we will test the hypothesis that mutations in that locus contribute to the development of renal disease in BBS, by leveraging extensive data from zebrafish models and testing the paradigm in the mouse. In parallel, using a combination of computational and biological tools, will ask whether discrete point mutations in that locus can account for the variable activity of the disease-causing allele p.P209L, a hypomorph in human but a null allele in the mouse. Finally, grounded on recent observations derived from a genome-wide genetic suppressor screen that augmentation of the proteasome ameliorates BBS in vitro and in vivo, we will employ our recently-developed proteasome sensor screening paradigm to perform a small molecule screen for new therapeutic leads. These studies will provide a comprehensive look at the architecture of a genetically heterogeneous, phenotypically variable exemplar disorder, while at the same time, allowing the rational discovery of new therapeutic paradigms.