Clinical Review

Update on prenatal exome sequencing

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Prenatal genetic testing is boldly going to the next frontier: exome sequencing. Here, experts consider studies that explore the technology’s potential utility and offer practical society guidance on use.


 

Prenatal diagnosis of genetic anomalies is important for diagnosing lethal genetic conditions before birth. It can provide information for parents regarding pregnancy options and allow for recurrence risk counseling and the potential use of preimplantation genetic testing in the next pregnancy. For decades, a karyotype was used to analyze amniocentesis and chorionic villus sampling specimens; in recent years, chromosomal microarray analysis provides more information about significant chromosomal abnormalities, including microdeletions and microduplications. However, microarrays also have limitations, as they do not identify base pair changes associated with single-gene disorders.

The advent of next-generation sequencing has substantially reduced the cost of DNA sequencing. Whole genome sequencing (WGS) can sequence the entire genome— both the coding (exonic) and noncoding (intronic) regions—while exome sequencing analyzes only the protein-coding exons, which make up 1% to 2% of the genome and about 85% of the protein-coding genes associated with known human disease. Exome sequencing increasingly is used in cases of suspected genetic disorders when other tests have been unrevealing.

In this Update, we review recent reports of prenatal exome sequencing, including studies exploring the yield in fetuses with structural anomalies; the importance of prenatal phenotyping; the perspectives of parents and health care professionals who were involved in prenatal exome sequencing studies; and a summary of a joint position statement from 3 societies regarding prenatal sequencing.

Prenatal whole exome sequencing has potential utility, with some limitations

Petrovski S, Aggarwal V, Giordano JL, et al. Whole-exome sequencing in the evaluation of fetal structural anomalies: a prospective cohort study. Lancet. 2019;393:758-767.

Lord J, McMullan DJ, Eberhardt RY, et al; for the Prenatal Assessment of Genomes and Exomes Consortium. Prenatal exome sequencing analysis in fetal structural anomalies detected by ultrasonography (PAGE): a cohort study. Lancet. 2019;393:747-757.

Exome sequencing has been shown to identify an underlying genetic cause in 25% to 30% of children with an undiagnosed suspected genetic disorder. Two studies recently published in the Lancet sought to determine the incremental diagnostic yield of prenatal whole exome sequencing (WES) in the setting of fetal structural anomalies when karyotype and microarray results were normal.

Continue to: Details of the studies...

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