Prenatal DNA diagnosis of Noonan syndrome in a fetus with increased nuchal translucency using next-generation sequencing

Exome sequencing improves genetic diagnosis of fetal increased nuchal translucency

OBJECTIVE

The aim of this retrospective study is to determine the monogenic syndromes in fetuses with isolated first-trimester increased nuchal translucency (NT) in order to provide more accurate parental counseling.

METHODS

Medical trio exome sequencing (ES) was performed on DNA extracted from chorionic villi in 73 fetuses with isolated first-trimester increased NT (≥3.5 mm) and normal chromosomal microarray analysis (CMA). This testing targets coding exons for 4200 clinically relevant disease-causing genes. The interpretation of variants was performed according to the American College of Medical Genetics guidelines.

RESULTS

Pathogenic variants were detected in four cases in which phenotypes and genotypes correlate well. Medical trio ES offered a 5.5% (4/73) increase in diagnostic rate over CMA in cases with isolated increased NT. Three of four cases with pathogenic variants developed structural anomalies on ultrasound at mid pregnancy, leading to the pregnancy termination. Only one case with a pathogenic variant demonstrated normal ultrasound throughout pregnancy.

CONCLUSION

Our results indicate that after a normal CMA, fetuses with isolated first-trimester increased NT have a 1.4% (1/73) risk of significant childhood genetic syndromes caused by known disease-causing variants, which will not be detectable on prenatal ultrasound. This information may be useful in parental counseling.

Co-occurrence of hypertrophic cardiomyopathy and juvenile myelomonocytic leukemia in a neonate with Noonan syndrome, leading to premature death

We report a case of a neonate with Noonan syndrome presenting with concurrent hypertrophic cardiomyopathy and juvenile myelomonocytic leukemia, which resulted in premature death. Cases with Noonan syndrome diagnosed during the neonatal period might not necessarily show mild clinical course, and premature death is a possible outcome to be considered.

Prenatal DNA Sequencing: Clinical, Counseling, and Diagnostic Laboratory Considerations

Clinical diagnostic laboratories are producing next-generation sequencing-based test results that are becoming increasingly incorporated into patient care. Whole genome and exome sequencing on fetal material derived from amniocytes, chorionic villi, or products of conception is starting to be offered clinically in specialized centers, but it has not yet become routine practice. The technical, interpretation, and ethical challenges are greatest in the area of prenatal medicine because the fetus has a limited health history, and the physical examination is only indirectly available via prenatal sonography. Here, we provide an overview of these challenges and highlight the clinical utility, reporting, and counseling issues associated with prenatal DNA sequencing. Future considerations are also discussed. © 2017 John Wiley & Sons, Ltd.