In a report published in the New England Journal of Medicine yesterday, two scientists have sketched out what doctors need to know in order to use genome-based sequencing technology effectively to diagnose illnesses, particularly rare childhood diseases. Leslie G. Biesecker, MD, of the National Human Genome Research Institute, and Robert C. Green, MD, MPH, of Brigham and Women’s Hospital and Harvard Medical School, Boston, note that several thousand physicians already have ordered clinical genome or exome sequencing (CGES) for their patients. Biesecker, chief of NHGRI’s Medical Genomics and Metabolic Genetics Branch, predicts that about 10,000 such tests will be ordered this year, and even more than that next year.
“The technologies that were used for the Human Genome Project are now distilled down to practical tools that clinicians can use to diagnose and, hopefully, treat diseases in patients that they couldn’t treat before,” Biesecker says. “It’s come much faster and developed more quickly, and become more useful clinically, than I think any reasonable person would have suggested just 10 years ago.”
Exome sequencing amounts to an abridged version of the more complete, but more costly, genome sequencing. Instead of targeting three billion base pairs of a human’s genome, exome sequencing focuses on the DNA segments, known as exons, that code for proteins. These make up 1% to 2% of the human genome and account for about 20,000 genes. Once a patient’s DNA is extracted and the exons sequenced, computer programs identify differences between the patient’s DNA and a reference sequence for the human genome. These variants may point to the cause of disease. Learn more from a National Institutes of Health news release.Read more