早发性严重视网膜营养不良一家系TULP1和CNGB1基因突变

Novel mutations in the TULP1 and CNGB1 genes in a family affected with early onset severe retinal dystrophy

目的确定早发性严重视网膜营养不良(EOSRD)一家系的致病基因突变。方法回顾性临床研究。2018年8月于河南省立眼科医院检查确诊的一个汉族EOSRD家系中1例患者及3名家系成员纳入研究。详细采集患者病史后,对受试者行最佳矫正视力(BCVA )、裂隙灯显微镜联合前置镜、眼底彩色照相、频域光相干断层扫描(SD-OCT)及全视野视网膜电图(ff-ERG)检查。采集受试者外周静脉血5 ml,提取全基因组DNA。应用包含441个致病基因的遗传眼病捕获芯片进行靶向捕获富集高通量测序,对明确的致病突变位点进行Sanger测序验证;应用分析软件对突变位点进行生物信息学分析。结果先证者女,6岁,于1岁以后出现双眼夜间视力差。双眼BCVA均为0.1。视盘颜色稍淡;视网膜血管管径稍变细,血管弓外视网膜可见广泛色素改变。SD-OCT检查可见双眼黄斑中心凹处外界膜、椭圆体带及嵌合体带结构欠清、断续;中心凹外可视区神经上皮外丛状层、外核层、外界膜、椭圆体带及嵌合体带逐渐消失,色素上皮层厚度欠均匀。ff-ERG检查,双眼视锥、视杆系统功能严重下降。基因检测结果显示,先证者Tubby样蛋白1 (TULP1)基因存在c.921C>A纯合突变,环核苷酸门控通道β1 (CNGB1)基因存在c.3121C>T、c.3488G>A复合杂合突变。氨基酸保守性分析结果显示,上述3个突变位点在多个物种中均高度保守。生物信息学分析结果显示,TULP1基因c.921C>A (p.Cys307*)在蛋白质保守区出现翻译终止,CNGB1基因c.3121C>T (p.Arg1041Trp)、c.3488G>A (p.Gly1163Glu)在蛋白质保守区出现氨基酸极性变化,导致蛋白质空间结构产生较大改变。结论 TULP1基因c.921C>A纯合突变、CNGB1基因c.3121C>T和c.3488G>A复合杂合突变为该EOSRD家系的突变位点。

Objective To identify the pathogenic gene mutations in a family with early onset severe retinal dystrophy(EOSRD).Methods A retrospective clinical study.One patient and three family members from a Han of EOSRD who were diagnosed at Henan Eye Hospital in August 2018 were included in the study.After the detailed history of the patients was collected,all participants underwent best corrected visual acuity(BCVA),slit-lamp,fundus biomicroscopy with the slit lamp,untra-widefield fundus color photography,spectral-domain optical coherence tomography(SD-OCT)and full-field electroretinography(ff-ERG).The subject's peripheral venous blood of 5 ml was collected and the whole genome DNA was extracted.A genetic eye disease capture chip containing 441 disease-causing genes was used for targeted capture and enrichment of high-throughput sequencing,and Sanger sequencing was performed for the clear pathogenic mutation sites;the analysis software was used for bioinformatics analysis of the mutation sites.Results A 6-year-old female proband developed poor night vision in both eyes after 1 year old.The BCVA of both eyes were 0.1.The color of the optic disc was slightly lighter;the diameter of the retinal vessels was slightly reduced,and extensive pigment changes can be seen in the retina outside the vascular arch.SD-OCT examination showed that the outer membrane,ellipsoid zone and chimera zone in the central fovea of both eyes were unclear and intermittent.The visual area outside the fovea was neuroepithelial outer plexiform layer,outer nuclear layer,outer membrane,ellipsoid zone.The chimera zone gradually disappeared,and the thickness of the pigment epithelial layer was not uniform.In ff-ERG examination,the functions of the binocular cone and rod system were severely decreased.The results of genetic testing showed that there were c.921C>A homozygous mutations in the Tubby-like protein(TULP1)gene of the proband,and c.3121C>T and c.3488G>A compound heterozygous mutations in the cyclic nucleotide gated channel beta 1(CNGB1)gene.Amino acid conservation analysis results showed that the above three mutation sites were highly conserved in multiple species;bioinformatics analysis results showed that TULP1 gene c.921C>A(p.Cys307^*)had translation termination in the protein conserved region,CNGB1 gene c.3121C>T(p.Argl041Trp)and c.3488G>A(p.Glyl 163Glu)had amino acid polarity changes in the protein conserved region,which led to major changes in the protein spatial structure.Conclusion TULP1 gene c.921C>A homozygous mutation,CNGB1 gene c.3121C>T and c.3488G>A compound heterozygous mutation are the mutation sites of this EOSRD family.