智力障碍致病基因突变对脑发育的影响及其机制

Intellectual disability (ID) is often caused by the gene mutations and chromosome abnormalities. However, it remains to be investigated whether there are specific ID-related gene mutations in Chinese population. To screen the ID-related gene mutations in Chinese ID children, we used gene sequencing and identified some novel gene mutations, including fibroblast growth factor 13 (FGF13) and solute carrier family 6 member 8 (SLC6A8). Our previous study has reported that FGF13 regulates axonal growth by polymerizing and stabilizing microtubules, and FGF13-deficient mice exhibit weakened learning and memory. In this project, we will study the pathogenicity and related mechanisms of mutations including FGF13 and SLC6A8 genes etc. We will perform the experiments such as whole genome sequencing, genetic analysis of family tree, induced human neuronal stem cells and neurons, construction of gene mutation knockin mice, electrophysiological recording and behavioral tests, to identify the roles of FGF13 and SLC6A8 gene mutations in ID. We will examine the effects of the gene mutations on the RNA function and protein translation, and the development and function of neurons and neural circuits, to reveal the mechanisms of pathogenicity. This study will provide ID-related pathogenic genes and mechanisms in Chinese population, and theoretical basis and methods for the clinical diagnosis of ID.

先天性智力障碍（智障）多由基因突变和染色体异常造成，中国人群智障是否有不同于其他人群的致病基因突变尚待研究。我们对中国智障儿童进行了基因测序筛查，发现了一些新的基因突变，包括成纤维细胞生长因子13（FGF13）和溶质运载蛋白家族6成员8（SLC6A8）等基因的点突变。我们以往的研究发现，FGF13通过作用于微管调控轴突发育，FGF13基因的缺失会导致小鼠学习和记忆能力下降。本项目将研究FGF13和SLC6A8等基因突变的致病性及其机制。通过全基因组测序、家系遗传学分析、诱导人源神经干细胞和神经元、位点突变的基因敲入小鼠构建、电生理记录和行为学检测等方法，确认FGF13和SLC6A8等基因突变的致病性，揭示其对自身RNA功能和蛋白质翻译、神经元和神经环路发育及功能的影响，解析其致病机制。本研究将发现中国人群中FGF13等基因突变及其智障致病机制，为临床筛查智障致病基因突变提供依据和技术方法。

先天性智力障碍(智障)多由基因突变和染色体异常造成。我们对患有严重智力障碍的中国汉族儿童进行基因组测序并筛选其基因突变，在其中三名男性患者中发现一个共有的单核苷酸多态性位点（SNP，Single nucleotide polymorphism），其位于成纤维细胞生长因子13（FGF13，Fibroblast growth factor 13，又称FHF2）基因的5’端非翻译区（5’-UTR，5’-untranslated region）。在HEK293细胞系以及患者来源的诱导多能干细胞系（iPSCs，Induced pluripotent stem cells）中，引入该多态性位点都可以降低FGF13蛋白质翻译水平，而FGF13是一种在发育的神经元中维持微管稳定所必需的蛋白。同时，通过物种同源性比较得到小鼠中Fgf13基因的位于5’端非翻译区的同源位点，并以此构建转基因的点突变小鼠，发现该小鼠的皮层发育过程中存在皮层神经元的迁移障碍，以及成年小鼠表现出学习和记忆能力的下降。进一步地，该多态性位点的突变能够降低Fgf13 5’-UTR与多聚嘧啶结合蛋白2（PTBP2，Polypyrimidine-tract-binding protein 2）的结合，从而导致在皮层神经元中FGF13蛋白质翻译的降低。因此，以上结果表明新发现的FGF13单核苷酸多态性位点通过降低FGF13蛋白翻译，导致大脑发育和认知功能的障碍。本研究有助于进一步理解FGF13对大脑发育的调控机制，并为临床上对智力障碍疾病的早期筛查和诊断提供新的鉴定位点和研究证据。