Modifiers of Retinal Phenotypes in Ciliopathies

影响纤毛结构和功能的遗传性病变引起广泛的遗传性 异质性和临床重叠的疾病，统称为纤毛病变， 以表型重叠和可变的遗传率和表现力为特征。在视网膜中， 纤毛在蛋白质通过光感受器的运输中起着不可或缺的作用，并且对视网膜结构至关重要 事实证明，进行性感光细胞变性是许多视网膜病变的标志， 纤毛病变越来越多的证据表明，在某些纤毛病变中发生突变的基因可能同时导致 病因和修饰等位基因在整个睫状体病谱，从而产生的想法，无论是顺式和反式 作用等位基因可导致纤毛病变患者的突变负荷， 了解纤毛病的遗传结构可能会告知表型 人类遗传疾病的变异性。为了探索这一概念，我们以前进行了无偏见的医学研究。 已知/预期对纤毛生物发生和功能重要的基因的重新测序， 不同严重程度的患者队列。在RPGRIP 1 L中，一种已知引起新生儿 致命的Meckel-Gruber综合征（MKS）和中度严重的Joubert综合征（JBTS），我们确定了一个 高度保守的A229 T改变，其存在于中间群体频率，并且显著地 在视网膜变性患者中富集。使用跨学科的方法，我们继续表明， Thr 229等位基因是一个非中性的改变，它破坏了RPGRIP 1 L和RPGR之间的直接相互作用， X连锁视网膜色素变性（XLRP）的最常见的遗传原因。这些数据为我们提供了机会 探索睫状体病视网膜表型中第二位点修饰的遗传机制， 开发可用于进一步探测此类现象的模型。我们提出两个目标。第一，动机是 有机会开发一个强大的模型来研究上位性，我们将通过引入A229 T变化来建模， 进入小鼠模型，随后将Thr 229等位基因杂交到具有致敏纤毛功能的细胞系中， 确定该等位基因是否会诱导或加剧视网膜表型。第二，因为我们的初步 数据提示RPGRIP 1 L也可能对非综合征性视网膜变性有上位等位基因，我们 将RPGRIP 1 L的突变分析扩展到非综合征患者的扩展队列， 匹配的控制。使用我们先前建立的体内互补策略，我们将测试 新发现的等位基因的致病潜力，并与功能数据授权，我们将确定 视网膜变性中RPGRIP 1 L等位基因的总体富集。我们的研究完成后， 候选修饰等位基因在视网膜变性患者中，产生新的模型来研究这种 现象，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.