[Study of de novo point mutations in known genes among patients with unexplained intellectual disability or developmental delay].

Objective: To analyze the de novo point mutations in known genes among patients with unexplained intellectual disability (ID) or developmental retardation (DD). Methods: A total of 120 outpatients with ID or DD were recruited in the Department of Neurology, Affiliated Children's Hospital of Capital Institute of Pediatrics between September 2015 and April 2017. Target gene sequencing was used to screen the candidate gene. The sequencing data were analyzed by a variety of bioinformatics software. Combining with the phenotypes of the patients, the candidate genetic/genomic variants were identified from next-generation sequencing data. The final pathogenicity of the genetic/genomic variants were interpreted according to the guideline of the American College of Medical Genetics and Genomics (ACMG) for variants after segregation analysis in the parents and necessary family members by Sanger sequencing. The comprehensive physiological function and signaling pathways of 20 disease genes with de novo point mutation discovery was also studied. Results: Among the 120 patients, 23 patients were found to carry clear pathological changes, and the incidence of de novo point variation was 19.2%. The patients included 12 males and 11 females, with an age of 2 months to 6-year-6-month. Five patients were diagnosed with early onset of epileptic encephalopathy. Seven had mental retardation type 5, 6, 8, 19, 20, 22, 39, respectively. Weill-Marchesani syndrome type 2 was found in one case, Wiedemann-Steiner syndrome in one case, Coffin-Siris syndrome in two cases, Rubinstein-Taybi syndrome in one case, GLUT1 deficiency syndrome in one case, Rett syndrome in one case, cardio-facio-cutaneous syndrome 3 in one case, neurodegeneration with brain iron accumulation in one case, corpus callosum local dysplasia in one case, and congenital fibrosis of the extra-ocular muscles in one case. A total of 20 novel mutations were reported in this study. No somatic mutation was found in the samples of 6 patients with mutation and their parents' peripheral blood DNA samples by amplicon-based deep sequencing. This study found that the main disease genes were involved in chromatin remodeling, transcriptional regulation, autophagy body assembly, MAPK signal pathway, DNA methylation, potassium, sodium ion transport, cell skeleton assembly and skeletal muscle development. These genes were significantly enriched in the following biological processes: Ras signaling pathways, transcription factor binding and cancer related signaling pathway. Conclusions: The etiology of children affected with intellectual disability or developmental delay is complex. Harmful de novo point mutation plays an important role in these diseases. Targeted exome/genome sequencing based on the core family is helpful for the molecular diagnosis of patients and the discovery of more genes.目的： 分析不明原因智力障碍或发育迟缓患儿已知基因的新生点变异。 方法： 收集首都儿科研究所附属儿童医院神经内科门诊2015年9月至2017年4月就诊的120例智力障碍或发育迟缓患儿，采用目标基因捕获测序技术进行遗传病因诊断，根据美国医学遗传学与基因组学学会对基因变异解读的指南，利用多种生物信息学软件分析测序数据，结合患儿的表型，对明确或疑似致病性基因变异采用Sanger测序方法进行验证及父母传递分析，同时对新生点变异患儿的致病基因的生理功能及分子信号通路进行比较。 结果： 120例患儿中发现23例携带明确致病性新生点变异，新生点变异发生率为19.2%，23例患儿中男12例、女11例，年龄2个月～6岁6个月。早发性癫痫脑病5例，精神发育迟滞5、6、8、19、20、22、39型各1例，Weill-Marchesani综合征2型1例，Wiedemann-Steiner综合征1例，Coffin-Siris综合征2例，Rubinstein-Taybi综合征1例，GLUT1缺陷综合征1例，Rett综合征1例，心面皮肤综合征3型1例，神经退行性变伴脑铁沉积1例，胼胝体局部发育不全1例，先天性眼外肌纤维化1例，其中共发现了20种新突变。对其中6例新生点变异的携带者及其父母外周血DNA样本进行基于扩增子的深度测序，均未发现体细胞变异。20个致病基因主要参与染色质重塑、转录调控、自噬体装配、MAPK信号通路、DNA甲基化、钾离子及钠离子转运、细胞骨架装配及骨骼肌发育等，显著富集于以下几个生物学过程：Ras信号通路、转录因子结合及癌症相关信号通路等。 结论： 智力障碍或发育迟缓病因复杂，有害的新生点变异在不明原因智力障碍或发育迟缓疾病发生中具有重要作用，基于核心家系的目标外显子组捕获测序有助于患者的明确诊断和更多基因的发现。.