利用高通量测序技术鉴定纤毛相关疾病-Joubert综合征的致病基因

Cilia/flagella are highly conserved microtubule-based organelles, which are present on almost every cell type in the human body. It served as a key organelle in numerous physiological and developmental processes. Defects in ciliary assembly and function lead to a wide range of human disease symptoms, including polycystic kidney disease, hydrocephalus, retinal degeneration, infertility etc., which collectively termed "ciliopathies". The list of ciliopathies and their associated genes continues to grow. Revealing the genetic mechamism of ciliopathies will give an insight to developing the molecular prenatal diagnosis technique to reduce the birth defect. It will also provide clues for ciliopathies therapy..Joubert syndrome (JBTS, OMIM 213300) or Joubert syndorme related disorders (JSRD) is the most common neurodevelopmental disorder among the "ciliopathies" spectrum, which are thought to be caused by disorder of structure and function of primary cilia..Joubert syndrome is characterized by cerebellar hypoplasia, ataxia, psychomotor delay and abnormal eye movement with a distinct mid-hindbrain malformation presenting the "molar tooth sign" on brain MRI. Although 22 genes have been found for JBTS, they count for less 50% of the case, and no relevant research work have been reported in China..We have recruited the JBST affected cases throughout the whole countries. We plan to investigate the genetic mechanism of Joubert syndrome combined high thoughout targeted genome sequencing with whole-exome sequencing. Till now, 12 out of 24 Joubert syndrome patients have been screened by targeted genome sequencing based on Ion Ampliseq platform, 6 of which were proved to be caused by the known causative genes and whole-exome sequencing was performed to the rest of 5 patients. We are aimed to screen at least 50 cases to get the genetic spectrum of Chinese JBTS and identify the new causative gene, which will facilitate prenatal diagnosis of JBTS and provide clues for the study of other ciliopathies.

纤毛是以微管为主要结构组成的亚细胞结构。纤毛结构及功能缺陷导致的人类疾病统称为“纤毛相关疾病”，是国外研究的热点。Joubert 综合征是一种罕见的神经系统发育疾病，属常染色体隐性遗传病，具有高遗传异质性。虽已发现22 个Joubert 综合征致病基因，但仍有60%病例未找到已知致病基因的突变，且未见中国人群相关研究。本课题以中国人群Joubert 综合征患者及家系为研究对象，结合多重扩增子靶向基因组测序、全外显子组捕获测序等技术鉴定其致病基因及突变位点。目前我们已对24个样本中的12个样本进行了已知致病基因的筛查和群体验证，并对5个未发现突变的样本进行了外显子组测序。我们拟进一步扩大样本量，在3年内完成50-100例样本的已知致病基因筛查，并利用全外显子组测序的方法鉴定新的Joubert综合征致病基因，不仅可以为该病的产前分子诊断奠定基础，也将为其它纤毛疾病的遗传机制解析提供线索。

Joubert综合征是一种罕见的神经系统发育疾病，主要特征是小脑蚓部发育不良，主要表现为常染色体隐性遗传的模式。其临床表现有肌张力减低、共济失调、发育迟缓、智力障碍、呼吸节律异常、眼球运动障碍等，部分患者合并视网膜、肾脏、肝脏、骨骼等多器官受累。目前国外研究已发现30多个Joubert综合征的致病基因，并对基因型和表型的关系做了初步探索。我们首次对中国人群Joubert综合征遗传机制进行系统的研究，完成了63个Joubet综合征家系样本的收集，建立了中国第一个Joubert综合征病友组织-Joubert综合征关爱之家；建立了基于多重扩增子技术以及高通量测序技术的Joubert综合征致病基因检测panel，完善了分析流程，目前已初步完成52个家系的测序工作，阳性率达到65.4%，为至少34个家庭明确了致病基因及位点，这些位点分别位于C5ORF42, CC2D2A, CEP290, AHI1, TMEM67, NPHP1，CSPP1, INPP5E, TCTN1等基因上，其中C5orf42是中国人群Joubert综合征最主要的致病基因，而CEP290的突变在Joubert综合征合并先天性黑曚的患儿中多见。这一研究是中国首次对该罕见病进行系统的研究，积累了该疾病的突变数据库，为该病的产前诊断及出生缺陷防治提供强有力的分子生物学支持。