Inborn Errors of Metabolism (IEM) are genetic disorders that affect the body's ability to break down and use certain nutrients. These disorders can cause a wide range of symptoms, including mental retardation, physical disabilities, and even death. IEMs are caused by mutations in genes that are responsible for the production of enzymes that are necessary for the body to break down and use certain nutrients. Treatment for IEMs typically involves dietary changes, enzyme replacement therapy, and/or medication.