三例Kleefstra综合征患儿的基因变异分析

Genetic analysis of three patients with Kleefstra syndrome

目的对3例Kleefstra综合征患儿进行EHMT1基因变异分析,探讨其可能的致病原因。方法采集患儿及其父母的外周血进行全外显子测序(whole exome sequencing,WES),其中基因拷贝数变异(copy number variation,CNV)应用Realtime-PCR验证,基因变异应用Sanger测序方法验证。结果基因测序结果显示例1的EHMT1基因存在c.823+1G>T剪接位点杂合变异,父母均未检测到变异,变异影响该基因的表达水平,根据美国医学遗传学与基因组学学会(American College of Medical Genetics and Genomics,ACMG)遗传变异分类标准与指南,判定为致病性变异(PVS1+PS2+PM2);例2的EHMT1基因存在c.439C>G(p.Leu147Val)杂合变异,父母均未检测到变异,根据ACMG遗传变异分类标准与指南,判定为可能致病性变异(PS2+PM1+PM2+PP3)。芯片结果提示例3在染色体9q34.3区域存在约520 kb的缺失,该缺失区域包括EHMT1基因,逆转录-PCR结果显示其父母该区域未见异常。结论EHMT1基因变异可能是3例患儿的致病原因,基因检测可以为临床诊断提供依据。

Objective To analyze the clinical and genetic features of three patient diagnosed with Kleefstra syndrome.Methods Whole exome sequencing(WES)was carried out for the probands and their parents.Suspected variants were validated by Sanger sequencing.Copy number variations(CNV)were detected by CNV-seq and validated by real-time PCR.Results Proband 1 was found to carry a de novo heterogeneous variant(c.823+1G>T)of the EHMT1 gene,which may affect its expression.Based on the guidelines of the American College of Medical Genetics and Genomics,the variant was predicted to be pathogenic(PVS1+PS2+PM2).Proband 2 was found to carry a de novo missense variant c.439C>G(p.L147V)of the EHMT1 gene,which was predicted to be likely pathogenic(PS2+PM1+PM2+PP3).Proband 3 was found to carry a heterozygous 520 kb deletion at 9q34.3 by CNV-seq.The deletion has encompassed the whole of the EHMT1 gene.Real-time PCR has detected no CNV of this region in her parents.Conclusion Variants of the EHMT1 gene probably underlay the disease in these paients.Genetic testing has provided a basis for their clinical diagnosis.