Clinical genomics: when whole genome sequencing is like a whole-body CT scan.

Although we have witnessed major improvements in genomic testing in the past 5 years, multiple challenges need to be solved before clinical genomic testing becomes routine (1 ). The clinical implementation of genomic testing parallels the challenges we have faced with other transformative technologies. For the past decade, the medical community has been discussing the impact on healthcare and society of direct-toconsumer marketed whole-body computed tomography (CT)8 scanning (2 ). The CT scan is a technology that uses X-rays to produce cross-sectional images of the human body. There are clinical scenarios in which the CT scan is invaluable: disease diagnosis, evaluation after trauma, and monitoring response to oncologic therapy. However, CT scan is also being marketed as a preventive diagnostic for healthy individuals (3 ). Genomics can parallel CT scanning in scenarios of (a) first line diagnostic testing, (b) last ditch diagnosis, and (c) inappropriate clinical use. Genomic testing implies the examination of the nucleic acid sequence of multiple, if not all, known genes. Broadly, this includes microarray tests that survey changes in single nucleotide polymorphisms (SNPs) and copy-number variation across the entire genome, sequencing the exome or whole genome by nextgeneration sequencing, and sequencing large panels of clinically significant genes. Genomic testing is currently moving from academic research practice to commercialization and direct-to-consumer marketing. Although genomic testing is not yet routine, DNA testing targeted to single genes, viruses, or bacteria is commonplace and performed in many clinical laboratories. The use of genetic information has evolved over the past decade from targeted single-gene tests to broader genomic tests that encompass thousands of genes. Numerous ethical, economic, and technological challenges need to be addressed before widespread adoption of clinical genomic testing. For example, a patient may not want to know their future risk of disease; a patient (and society) may not be able to afford genomic testing. In addition, genomic testing may not be appropriate for all diseases.