An inborn error of metabolism in which the body lacks the ability to break down the amino acid fenylananin in the blood, causing accumulation of phenylalanine and its metabolic products in body tissues and fluids. It is the most common inborn error of the amino acid metabolism. The affected children, who are usually blond and blue-eyed, appear normal at birth but psychomotor developments is delayed and mental retardation begins during the first year of life. The mental defect is severe. Other neurologic manifestations include seizures, hyperkinesia, aggressive behaviour, and microcephaly. Inability to talk or walk are common features. Both sexes equally affected. Inheritance is autosomal recessive. The syndrome is most common in northern Europe. The disease is discovered by a urine test – Følling's test. The patient may have a normal development if a strict diet is followed.
Other variants of phenylketonuria are Phenylketonuria II (PKU II, dihydropteridine reductase deficiency) and Phenylketonuria, Tourian and Sidbury type (hyperphenylalaninemia VI).
- A. Følling:
Über Ausscheidung von Phenylbrenztraubensäure in den Harn als Stoffwechselanomalie in Verbindung mit Imbezilität.
Hoppe-Seylers Zeitschrift für physiologische Chemie, 1934, 227: 169-176.
- K. Bartholome, D. J. Byrd:
Tetrahydrobiopterin treatment of variant form of phenylketonuria.
The Lancet, London, 1975, 2: 1042.
- A. Y. Tourian, J, B. Sidbury:
In: J. B. Stanbury, J. B. Wyngaarden, D. S. Fredrickson, editors: Metabolic Basis of Inherited Disease. 4th edition, New York, McGraw-Hill, 1978, pp. 240-255.