Phenylketonuria (PKU) is an inherited genetic disorder that interferes with the metabolism of a specific amino acid. Those born with it are unable to process part of a protein called phenylalanine (Phe). All babies born in U.S. hospitals must have a screening test for PKU. This makes it easier to diagnose and treat the problem early. Many adults with PKU who were diagnosed through newborn screening and have been treated since birth have high educational achievement, successful careers, and fulfilling family lives.