Yale University researchers have made a clinical relevant diagnosis for the first time using comprehensive DNA sequencing of all the protein-coding genes in the genome.  Called whole exome sequencing because it selectively analyzes the 1 % of the genome that contains genes that code for proteins, this new approach is a marriage of advanced DNA sequencing technology and microarray protocols that can selectively sequence protein-coding regions of the genomes. The methodology can identify genetic mutations with great precision at a cost 10 to 20 times less than sequencing the entire genome.  In this first-ever successful application of this technology, the information changed the course of treatment of a baby boy suffering from symptoms of dehydration thousands of miles away in Turkey. The Yale team was asked conduct the genetic study by a Turkish doctor with a five-month old patient suspected to have Bartter syndrome, a potentially fatal kidney problem that causes dehydration. After sequencing the protein-coding parts of his DNA, the Yale team found that the initial diagnosis was incorrect. The baby actually had a mutation in a gene that causes problems in the intestines, leading to congenital chloride diarrhea. By only sequencing the parts of the genome that code for proteins, they were able perform the analysis for about a tenth the cost.  “We believe this heralds the dawn of a new era in genetics and personalized medicine,” predicts Richard Lifton, from Yale University’s Department of Genetics.