Modifiers of Retinal Phenotypes in Ciliopathies

影响纤毛结构和功能的遗传性损害导致了广泛的遗传性 异质性和临床重叠的疾病，统称为纤毛疾病，这些疾病是 以表型重叠和可变的外显率和表现力为特征的。在视网膜中，一种改良的 纤毛在光感受器的蛋白质运输中起着不可或缺的作用，对视网膜结构至关重要。 和功能，这一事实从进行性感光细胞退化是许多 纤毛病。越来越多的证据表明，在某些纤毛疾病中突变的基因可能对两者都有贡献 纤毛病谱中的因果和修饰等位基因，引发了顺式和反式的想法 作用等位基因可导致睫状肌病患者的突变负荷，并提供了一种可能性 了解纤毛疾病的遗传结构可能会揭示表型背后的机制 人类遗传疾病中的可变性。为了探索这一概念，我们之前已经进行了公正的医疗 已知/预期对大型临床纤毛生物发生和功能重要的基因的重新测序 不同的患者队列，严重程度各不相同。在RPGRIP1L中，一种已知导致新生儿的基因 致命的Meckel-Gruber综合征(MKS)和中度严重的Joubert综合征(JBTS)，我们发现了一个 高度保守的A229T改变，存在于中等群体频率，并显著 富含于视网膜退行性变患者。使用跨学科的方法，我们继续展示了 Thr229等位基因是一种非中性的改变，它破坏了RPGRIP1L和RPGR之间的直接相互作用， X-连锁视网膜色素变性(XLRP)最常见的遗传原因。这些数据为我们提供了机会 探讨睫状体病变视网膜表型第二位点修饰的遗传机制(S)，并 开发可用于进一步研究此类现象的模型。我们提出了两个目标。首先，动机是 有机会开发一个稳健的模型来研究上位性，我们将通过引入A229T来对其变化进行建模 并随后将Thr229等位基因杂交成具有敏化睫毛功能的系 确定该等位基因是否会诱发或加剧视网膜表型。第二，因为我们的初选 数据表明，RPGRIP1L也可能在非综合征性视网膜变性中贡献上位等位基因，我们 将RPGRIP1L的突变分析扩大到非综合征患者的扩大队列，并 配对的对照组。使用我们之前建立的体内互补策略，然后我们将测试 新发现的等位基因的致病潜力，并赋予功能数据，我们将确定 RPGRIP1L等位基因在视网膜变性中的全面富集性。我们的研究完成后，将会确定 视网膜变性患者的候选修饰等位基因，产生了研究此类疾病的新模型 并有可能告知表型变异的遗传基础，这反过来又会 有助于更好地诊断和长期管理患者。

Genetic lesions affecting ciliary structure and function give rise to a broad collection of genetically heterogeneous and clinically overlapping disorders, known collectively as the ciliopathies, which are characterized by both phenotypic overlap and variable penetrance and expressivity. In the retina, a modified cilium plays an integral role in protein transport across the photoreceptor and is critical for retinal architecture and function, as evidenced by the fact that progressive photoreceptor degeneration is a hallmark of numerous ciliopathies. Accumulating evidence suggests that genes mutated in some ciliopathies can contribute both causal and modifying alleles across the ciliopathy spectrum, giving rise to the idea that both cis and trans acting alleles can contribute to the mutational load of ciliopathy patients and offer the possibility that understanding the genetic architecture of ciliopathies might inform the mechanisms that underlie phenotypic variability in human genetic disorders. To explore this notion, we have previously conducted unbiased medical resequencing of genes known/expected to be important to ciliary biogenesis and function in a large, clinically diverse cohort of patients that span the spectrum of severity. In RPGRIP1L, a gene known to cause neonatal lethal Meckel-Gruber Syndrome (MKS) and moderately severe Joubert Syndrome (JBTS), we identified a highly-conserved A229T change which was present at intermediate population frequency, and was significantly enriched in patients with retinal degeneration. Using an interdisciplinary approach, we went on to show that the Thr229 allele is a non-neutral change that disrupts the direct interaction between RPGRIP1L and RPGR, the most frequent genetic cause of X-linked Retinitis Pigmentosa (XLRP). These data offer us the opportunity explore the genetic mechanism(s) of second-site modification in retinal phenotypes in ciliopathies, and to develop models that can be used to probe such phenomena further. We propose two aims. First, motivated by the opportunity to develop a robust model to study epistasis, we will model the A229T change by introducing it into a mouse model and subsequently crossing the Thr229 allele into lines with sensitized ciliary function to determine if this allele will either induce or exacerbate retinal phenotypes. Second, because our preliminary data suggest that RPGRIP1L might also contribute epistatic alleles to non-syndromic retinal degeneration, we will expand the mutational analysis of RPGRIP1L to an extended cohort of non-syndromic patients and matched controls. Using our previously established in vivo complementation strategy, we will then test the pathogenic potential of newly discovered alleles, and, empowered with functional data, we will determine the overall enrichment of RPGRIP1L alleles in retinal degeneration. The completion of our studies will identify candidate modifier alleles in patients with retinal degeneration, generate new models to study such phenomena and has the potential to inform the genetic basis of phenotypic variability, which in turn will contribute to the better diagnosis and long-term management of patients.