Phenylketonuria (PKU) is a rare metabolic disorder that is caused by a deficiency of the enzyme phenylalanine hydroxylase. This enzyme is responsible for converting the amino acid phenylalanine into tyrosine, which is essential for normal development and metabolism. As a result, when a person has PKU, an excess of phenylalanine builds up in their body, and if not treated, can lead to serious health complications.
The medical term for PKU is phenylketonuria, but it is also sometimes referred to as "PKU syndrome" or "Følling's disease". It was first described in 1934 by a Norwegian physician, Asbjørn Følling, who noticed that the urine of some of his patients had an unusual odor and contained an unusual compound, phenylpyruvic acid. Følling's work led to the discovery of the enzyme deficiency responsible for the disorder, and the term "phenylketonuria" was coined in his honor.