 Approximately one in three admissions to tertiary care pediatric hospitals results from conditions with a genetic basis. Although the majority of these conditions are rare, they collectively account for a disproportionate amount of illness and death in children. Discovery of the genetic basis of rare conditions often uncovers the pathophysiological basis of common diseases. This is particularly true for genetic diseases of impaired metabolism inborn errors of metabolism, IEMs. There are many more genetic and metabolic disorders yet to be discovered. Of approximately 20,000 known human genes, less than one-fifth are currently associated with a disease phenotype. IEMs are a particular area of focus for us for two major reasons. First, of the several hundred known IEMs, many are already effectively treated with dietary modifications andor medical therapy. This indicates to us that discovery of new IEM genes has great potential to produce clinically actionable insights into pathophysiology and therapeutic opportunities, ultimately leading to treatment of children that would otherwise be impossible to treat. Second, the PI of this study, Dr. Ralph DeBerardinis, is an expert in metabolomics, the practice of identifying and quantifying metabolites from biological systems. We will therefore implement research-based metabolomic profiling to the evaluation of patients with suspected IEMs or other genetic diseases. This detailed analysis will substantially increase the likelihood of identifying clinically relevant metabolic perturbations in children with growth failure, acidosis, hypoglycemia, hyperammonemia, and other abnormalities of putative genetic origin. It would also enable us to interpret mutations uncovered by clinical or research-based genomic sequencing. We believe that establishing a systematic procedure to evaluate both the metabolome and the genome in sick children will produce new insights into the genetic basis of pediatric disease, and ultimately new ways to treat these conditions. 