Abstract
Phenylketonuria (PKU) is a hereditary metabolic disorder characterized by the inability to metabolize phenylalanine, leading to neurotoxic accumulation of phenylalanine and significant cognitive impairment. While extensive research has focused on the cognitive outcomes in middle childhood, adolescence, and early adulthood, there is a notable paucity of studies addressing the cognitive functioning of very young and older PKU patients. This review underscores the necessity for further research in these populations, particularly because of the importance of early cognitive development for later cognitive and behavioral functioning and because of the potential implications of PKU and metabolic control for age-related cognitive decline.