Clinical Utility of Prenatal Whole Exome Sequencing

Next-generation sequencing (NGS) is changing the paradigm of clinical genetic testing. Unlike highly focused single-gene tests, NGS allows one to examine gene panels, the exome, and the whole genome. With the broad array of molecular tests now available, ordering physicians face the conundrum of selecting the best diagnostic tool for patients with suspected genetic conditions. Single-gene testing is often most appropriate for conditions with distinctive clinical features and minimal locus heterogeneity. NGS-based gene panel testing, which can be complemented with chromosomal microarray analysis (CMA) and other ancillary methods, provides a comprehensive and feasible approach for well documented but genetically heterogeneous disorders. Whole exome sequencing (WES) and whole genome sequencing (WGS) have the advantage of enabling parallel interrogation of most of the genes in the human genome. To some, WES is preferable to previously used methods due to higher diagnostic yield, shorter time to diagnosis, and improved cost-efficiency.

The ability to survey the exome opens up both new opportunities and new challenges. For example, all coding regions of known genes must be analyzed when applying WES to undiagnosed cases with unclear inheritance patterns. Current limitations on variant interpretation capabilities and clinical validity raise questions about the clinical utility of WES as either a stand-alone or a first-choice diagnostic test. Additional challenges include pre- and post-test counseling with appropriate and robust informed consent, bioinformatics analysis setup and validation, variant interpretation and classification, the need for policies and protocols concerning the discovery and reporting of secondary findings unrelated to the presenting indication, a requirement for validation of WES results, assurance of conformation to quality control standards, data storage and accessibility, and reimbursement issues.

Current clinical standards recommend offering chromosomal microarray (CMA) in the prenatal setting when fetal structural anomalies are detected via prenatal ultrasound. In these cases, clinically relevant copy number variants have been reported in 6.0-9.1% of fetuses with a normal karyotype. However, informed consent processes for prenatal CMA are challenging-particularly in cases with ultrasound anomalies, as parents are absorbing challenging news and under considerable stress. Women have reported being "blindsided" by positive CMA results, or feeling that these results were "toxic information"-information they wished they did not have, particularly in cases of uncertain genetic information or uninterpretable variants. Nonetheless, in that same study women who were referred for CMA because of ultrasound anomalies reported less frequent negative reactions, since they already anticipated abnormal results.

Introducing WES into prenatal clinical care of underrepresented populations raises additional issues and considerations of payment coverage, access, and standards of care. Beyond the sheer complexity of the test and its results, clinicians and health systems must address numerous considerations, including: private and public insurance coverage; language and culture differences and their implications for genetic counseling and clinician-patient relationships; ability to access follow-up testing and clinical care; ability to access appropriate treatment and services; and particularly in the prenatal setting, local, state, and national abortion laws and decision-making about pregnancy termination. These issues and others will affect not only patients' decision-making regarding WES, but also their post-test needs for patient follow up, counseling and support. The importance of systematically assessing the clinical utility of NGS is critical for determining in which clinical and health care contexts WES will be useful and for commencing research on these considerations.

The investigator aims to examine the clinical utility of WES, including assessment of a variety of health-related and reproductive outcomes in undiagnosed prenatal cases.