Sequencing a patient’s entire genome to discover the source of his or her disease is not routine – yet. But geneticists are getting close. A case report, published February 2, 2012 in the American Journal of Human Genetics, shows how researchers can combine a simple blood test with an “executive summary” scan of the genome to diagnose a type of severe metabolic disease. Researchers at Emory University School of Medicine and Sanford-Burnham Medical Research Institute used “whole-exome sequencing” to find the mutations causing a glycosylation disorder in a boy born in 2004. Mutations in the gene (called DDOST) that is responsible for the boy’s disease had not been previously seen in other cases of glycosylation disorders. Whole-exome sequencing is a cheaper, faster, but still efficient strategy for reading the parts of the genome scientists believe are the most important for diagnosing disease. The report illustrates how whole-exome sequencing, which was first offered commercially for clinical diagnosis in 2011, is entering medical practice. Emory Genetics Laboratory is now gearing up to start offering whole-exome sequencing as a clinical diagnostic service. It is estimated that most disease-causing mutations (around 85 percent) are found within the regions of the genome that encode proteins, the workhorse machinery of the cell. Whole-exome sequencing reads only the parts of the human genome that encode proteins, leaving the other 99 percent of the genome unread. The boy in the case report was identified by Dr. Hudson Freeze and his colleagues. Dr. Freeze is director of the Genetic Disease Program at Sanford-Burnham Medical Research Institute. A team led by Dr. Madhuri Hegde, associate professor of human genetics at Emory University School of Medicine and director of the Emory Genetics Laboratory, identified the gene responsible.
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