Looking back at the neonatal period in early-treated phenylketonuric patients

Current research on the clinical outcome of phenylketonuria (PKU) patients has mainly explored the possible consequences of late exposure to high phenylalanine (Phe) levels in early-treated adult and elderly patients. However, despite the progressively earlier diagnosis and treatment of PKU, the neonatal and infancy periods remain the most vulnerable periods of the brain to Phe, which may cause permanent impairment of early- and late-emerging cognitive functions. The few studies that have measured Phe exposure during the first month of life, before metabolic control is achieved, confirm Phe exposure during the first month as a factor contributing to the final outcome of the disease.