Asbj�rn F�lling and the Discovery of Phenylketonuria

In 1934, the Norwegian biochemist and physician Asbjørn Følling described an inherited metabolic disorder characterized by severe intellectual impairment, motor problems, and skin abnormalities. He found that affected individuals could be identified by the abnormal excretion of phenylpyruvic acid in their urine. The disorder, which Følling initially termed imbecillitas phenylpyrouvica, would later come to be known as phenylketonuria or PKU. The present paper focuses on the story of Følling's discovery and his subsequent contributions to the area of study. In the years that have followed, research on PKU has continued to play a major role in the neurosciences, shaping our understanding of genetic disorders, human metabolism, and brain development.