The UCGS Exome Sequencing Test evaluates the protein-coding regions of the human genome, which represents approximately 20,000 genes. These regions of DNA are referred to as ‘exome’. The exome accounts for approximately 2% of the genome and comprises the majority of DNA variations that cause human disease. Exome sequencing is a useful and powerful tool for diagnostic applications and has been utilized to identify mutations in disorders that are both genetically and phenotypically heterogeneous and to identify mutations in genes associated with Mendelian disorders. Exome sequencing has been observed to identify the underlying genetic defect in approximately 25 – 35% of patients referred for evaluation of a possible genetic condition.