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Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by a deficiency in the hepatic enzyme phenylalanine hydroxylase (PAH).[1]:541 This enzyme is necessary to metabolize the amino acid phenylalanine ('Phe') to the amino acid tyrosine. When PAH is deficient, phenylalanine accumulates and is converted into phenylpyruvate (also known as phenylketone), which is detected in the urine.[2]

Since its discovery, there have been many advances in its treatment. It can now be managed by the patient with little or no side-effects other than the inconvenience of managing the treatment. If, however, the condition is left untreated, it can cause problems with brain development, leading to progressive mental retardation, brain damage, and seizures. In the past, PKU was treated with a low-phenylalanine diet. Latter-day research now has shown that diet alone may not be enough to prevent the negative effects of phenylalanine levels. Optimal treatment involves lowering blood Phe levels to a safe range and monitoring diet and cognitive development. Lowering of phenylalanine levels to a safe range may be achieved by combining a low-phenylalanine diet with protein supplements. There is currently no cure for this disease; however, some treatments are available with varying success rates. In general, PKU is detected through newborn screening and diagnosed by a geneticist. PKU clinics around the world provide care for PKU patients to optimize phe levels, dietary intake, and cognitive outcomes.



Phenylketonuria was discovered by the Norwegian physician Ivar Asbjørn Følling in 1934[3] when he noticed that hyperphenylalaninemia (HPA) was associated with mental retardation. In Norway, this disorder is known as Følling's disease, named after its discoverer.[4] Dr. Følling was one of the first physicians to apply detailed chemical analysis to the study of disease. His careful analysis of the urine of two affected siblings led him to request many physicians near Oslo to test the urine of other affected patients. This led to the discovery of the same substance that he had found in eight other patients. The substance found was subjected to much more basic and rudimentary chemical analysis (taste). He conducted tests and found reactions that gave rise to benzaldehyde and benzoic acid, which led him to conclude the compound contained a benzene ring. Further testing showed the melting point to be the same as phenylpyruvic acid, which indicated that the substance was in the urine. His careful science inspired many to pursue similar meticulous and painstaking research with other disorders.

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