三个连续发生非免疫性胎儿水肿家系的父母-胎儿全外显子测序分析

Analysis of three families with recurrence of non-immune hydrops fetalis by trio whole exome sequencing

目的对3个连续发生非免疫性胎儿水肿(non-immune hydrops fetalis,NIHF)的家系进行分析,探讨在拷贝数变异测序(copy number variation sequencing,CNV-seq)结果为阴性时,联合父母-胎儿全外显子测序(trio whole exome sequencing,trio WES)在明确非免疫性胎儿水肿病因中的应用价值。方法收集孕妇妊娠的羊水或胎儿流产物,对孕妇羊水进行CNV-seq检测,确认结果为阴性后,取胎儿双亲外周血进行trio WES。结果家系1胎儿检测出SOX18基因c.976G>T(p.Glu326*)杂合变异,RYR1基因c.844C>T(p.Arg282Trp)和c.9472+1G>A复合杂合变异,这3个变异遗传自胎儿父母,根据美国医学遗传学以及基因组学学会(American College of Medical Genetics and Genomics,ACMG)遗传变异分类标准与指南,SOX18基因c.976G>T变异为致病性变异(PVS1+PM2+PP3+PP4),RYR1基因c.844C>T变异为可能致病性变异(PM1+PM2+PP3),RYR1基因c.9472+1G>A变异为致病性变异(PVS1+PM2+PP3);家系2胎儿检测出PIEZO1基因c.6682C>T(p.Gln2228*)和c.4373_4383del(p.Val1458Alafs*63)复合杂合变异,这两个变异遗传自胎儿父母,根据ACMG指南评级证据,PIEZO1基因c.6682C>T变异和c.4373_4383del变异均判定为致病性变异(PVS1+PM2+PP4,PVS1+PM2);家系3检测出TTN基因c.29860G>C(p.Asp9954His)和c.21107A>T(p.Asp7036Val)复合杂合变异,这两个变异遗传自胎儿父母,基因变异有临床意义,考虑可以解释胎儿表型,根据ACMG指南评级证据,TTN基因c.29860G>C变异和c.21107A>T变异均为可能致病性变异(PM1+PM2+PP3)。结论建议在胎儿确诊为NIHF以后,同时进行CNV-seq和trio WES的检测,trio WES可在CNV-seq检测结果为阴性时提高其检出率。

Objective To explore the genetic basis of three families with recurrence of non-immune hydrops fetalis(NIHF)but negative result by copy number variation sequencing(CNV-seq).Methods Amniotic fluid sample and/or abortive tissues of the fetuses were collected and subjected to CNV-seq analysis.Peripheral blood samples of the parents were also taken for trio whole exome sequencing(trio WES).Results Fetus 1 was found to harbor heterozygous c.976G>T(p.Glu326*)variant of the SOX18 gene in addition with compound heterozygous variants c.844C>T(p.Arg282Trp)and c.9472+1G>A of the RYR1 gene.The three variants were all inherited from its parents and have been associated with the etiology of NIHF.Based on the American College of Medical Genetics and Genomics(ACMG)standards and guidelines,the c.976G>T variant of SOX18 gene and c.9472+1G>A of RYR1 gene were predicted to be pathogenic(PVS1+PM2+PP3+PP4,PVS1+PM2+PP3),and c.844C>T variant of RYR1 gene to be likely pathogenic(PM1+PM2+PP3).Fetus 2 was found to harbor compound heterozygous variants c.6682C>T(p.Gln2228*)and c.4373_4383del(p.Val1458Alafs*63)of the PIEZO1 gene.Both variants were also inherited from its parents and are associated with the etiology of NIHF.Based on ACMG standards and guidelines,both c.6682C>T and c.4373_4383del variants of PIEZO1 gene were predicted to be pathogenic(PVS1+PM2+PP4,PVS1+PM2).Fetus 3 was found to harbor compound heterozygous variants of the TTN gene c.29860G>C(p.Asp9954His)and c.21107A>T(p.Asp7036Val),which were respectively inherited from its parents.Both variants have been strongly associated with the phenotype,though the connection between the etiology of NIHF and variants of the TTN gene remains elusive.Based on ACMG standards and guidelines,the c.29860G>C and c.21107A>T variants of TTN gene were predicted to be likely pathogenic(PM1+PM2+PP3).Conclusion Trio WES can improve the diagnosis rate of NIHF with a negative result by CNV-seq.Considering the urgency of prenatal diagnosis,CNV-seq and trio WES should be carried out at the same time for fetuses with NIHF.