Inborn Errors of Metabolism Inborn errors of metabolism are rare genetic disorders that affect the body’s metabolism. Metabolism describes the body’s ability to convert food and drink into energy, as well as get rid of certain wastes made during that process. It’s a complex process that uses many different chemicals, enzymes, hormones, cells, and organs to work properly. With inborn errors of metabolism, certain enzymes don’t work properly or the body doesn’t make enough of an enzyme. This disrupts the process of metabolism. The body may be blocked from using substances it needs to function. Or, waste substances can build up in the body and become toxic. These issues can cause health problems, including serious developmental problems in young children. There are several different inborn errors of metabolism, including: Fructose intolerance Fructose intolerance Maple sugar urine disease (MSUD) Phenylketonuria (PKU) Urea Cycle Disorder (UCD)