Triplet repeat expansion-associated inherited corneal disease: from genetic mechanism to clinical consequences

Fuchs角膜内皮营养不良（FECD）是一种常见的视力损害疾病，影响4.5%的50岁以上的人群。双眼通常都会受到影响，这是因为角膜，眼睛前面的透明窗口，失去了从外层去除多余液体的能力，变得肿胀和浑浊。晚期FECD的唯一有效治疗方法是角膜移植。在英国，80%的FECD病例是由一种称为“CTG18.1重复扩增”的常见遗传疾病引起的，这种遗传密码的短序列重复并扩展到导致疾病的阈值。FECD是英国角膜移植最常见的原因。然而，手术费用昂贵，而且全球供体组织短缺。为了减少对角膜组织的需求，多种创新的治疗方案正在出现，包括我们实验室开发的基因疗法。这些疗法的长期成功将依赖于识别有发生FECD风险的个体，并在不可逆损伤发生之前开始早期治疗。更好地了解FECD的遗传机制将有助于实现这些目标。在其他更好地理解的疾病引起的异常重复的遗传密码（如。强直性肌营养不良），致病遗传密码重复越多，发病越早，患者症状越严重。此外，这些重复的遗传密码的数量在受影响的组织中更大。我们还知道，在这些情况下，当疾病从一代传到下一代时，致病遗传密码的数量会增加，导致每一代人更早和更虚弱的疾病。该项目旨在了解这些临床上重要的模式是否也发生在FECD中，FECD目前是一种知之甚少的疾病。我们的研究将在UCL眼科研究所的实验室环境中进行，在那里我们已经对一大群FECD患者进行了广泛的遗传分析。目标1.我将生成新的遗传数据，并使用统计模型来检查我们招募的患者的CTG18.1重复数与他们需要角膜移植时的年龄之间的关系。根据我的初步工作，我希望看到CTG18.1重复序列较大的患者更早需要角膜移植的趋势。这些知识将使我们能够根据遗传信息预测疾病进展的速度。目标二。我将使用一种称为单分子（SM）-PCR的创新技术来分析角膜移植手术期间从FECD患者中取出的受影响角膜组织中的DNA。由于技术限制，以前没有成功地进行过患病角膜细胞的分析。由于角膜是受FECD影响的唯一组织，我预测角膜细胞中CTG18.1重复的数量可能比同一患者的血细胞中的多得多。目标3：我将分析FECD患者的兄弟姐妹的DNA，以评估携带CTG18.1扩增的个体也发展FECD的比例。还将招募FECD患者的成年子女，以发现重复序列在传递给后代时的行为（即它是否变大或变小）。这将使我们能够更好地了解CTG18.1在家庭中的变化及其与FECD相关的风险。目前，尚不清楚FECD的致病基因如何改变其临床特征。这项重要的研究将帮助我们更深入地了解FECD，并可能使医生能够就FECD的进展及其对下一代FECD患者的风险影响提供更准确的遗传咨询。对受影响角膜细胞中CTG18.1重复序列的了解也可能为新的治疗选择开辟研究。

Fuchs endothelial corneal dystrophy (FECD) is a common vision-impairing disease that affects 4.5% of the population over 50 years of age. Both eyes are generally affected, and this is because the cornea, the transparent window at the front of the eye, loses its ability to remove excess fluid from its outer layers and becomes swollen and cloudy. The only effective treatment for advanced FECD is corneal transplantation. In the UK, 80% of the FECD cases are caused by a common genetic disorder called a 'CTG18.1 repeat expansion', where this short sequence of genetic code repeats and expands to a threshold that causes disease. FECD is the most common reason for corneal transplant in the UK. However, the surgery is costly, and there is a global shortage of donor tissue. In an effort to reduce the demand for corneal tissue, multiple innovative treatment options are emerging, including a gene therapy developed at our lab. The long-term success of these therapies will rely on identifying individuals at risk of developing FECD and initiating early treatment before irreversible damage occurs. Having a better understanding of the genetic mechanism in FECD would help to achieve these. In other better-understood diseases caused by abnormally repeated genetic codes (eg. myotonic dystrophy), the more the disease-causing genetic code is repeated, the earlier the onset of disease and the more severe symptoms patients will have. Moreover, the number of these repeated genetic codes is larger in the affected tissues. We also know that in these conditions, the number of the disease-causing genetic code increases when the disease is passed down from one generation to the next, resulting in earlier and more debilitating disease in each succeeding generation. This project aims to find out whether these clinically important patterns also occur in FECD, which is currently a poorly understood disease. Our study will take place in the laboratory setting at UCL Institute of Ophthalmology, where we have already performed extensive genetic analysis of a large group of FECD patients. Aim 1. I will generate new genetic data and use statistical models to examine the relationship between the number of CTG18.1 repeats of our recruited patients and their age when they require a corneal transplant. Following my preliminary work, I expect to see a trend where patients with larger CTG18.1 repeats require corneal transplants earlier. This knowledge will enable us to predict how fast disease will progress based on genetic information. Aim 2. I will use an innovative technique called Single Molecule (SM)-PCR to analyse the DNA in the affected corneal tissues removed from FECD patients during corneal transplant surgery. Due to technical limitations, analysis of diseased corneal cells has not been successfully performed before. As the cornea is the only tissue affected by FECD, I predict the number of CTG18.1 repeats in corneal cells may be a lot larger than in the blood cells of the same patient. Aim 3. I will analyse the DNA of FECD patients' siblings to assess the proportion of individuals carrying the CTG18.1 expansion that also develop FECD. Adult children of FECD patients will also be recruited to discover how the repeats behave (i.e. if it gets bigger or smaller) when passed onto successive generations. This will enable us to have a better understanding of how CTG18.1 changes within families and its risk associated with FECD. Currently, it is not known how the disease-causing gene of FECD modifies its clinical features. This important research will help us gain more in-depth knowledge about FECD, and potentially allow doctors to give more accurate genetic counselling on the progression of FECD and its risk implication to the next generation of FECD patients. Knowledge of CTG18.1 repeats in affected corneal cells may also open up research for new treatments options.