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Phenylketonuria (PKU)

Phenylketonuria (PKU) is an inborn error of metabolism involving impaired metabolism of phenylalanine, one of the amino acids. Untreated PKU can lead to intellectual disability, seizures, and other serious medical problems.

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About PKU

Phenylketonuria (pronounced fen-l-kee-toh-NOOR-ee-uh), often called PKU, is an inherited disorder that that can cause intellectual and developmental disabilities (IDDs) if not treated. In PKU, the body can't process a portion of a protein called phenylalanine, which is in all foods containing protein. If the phenylalanine level gets too high, the brain can become damaged.

All children born in U.S. hospitals are tested routinely for PKU soon after birth, making it easier to diagnose and treat affected children early.

Children and adults who are treated early and consistently develop normally.

Depending on the level of phenylalanine and tolerance for phenylalanine in the diet, PKU is classified into two different types: classic, which is the severe form, and moderate. Therefore, each patient needs an individualized treatment plan. Some people may benefit from a medication called sapropterin dihydrochloride (brand name Kuvan®) that treats the disorder...Read more about PKU NIH - National Institute of Child Health and Human Development

What works? Research summarized

Evidence reviews

Systematic review of large neutral amino acids for treatment of phenylketonuria

Bibliographic details: Lindegren ML, Krishnaswami S, Reimschisel T, Fonnesbeck C, Sathe NA, McPheeters ML.  Systematic review of large neutral amino acids for treatment of phenylketonuria. Journal of Pediatric Biochemistry 2013; 3(4): 181-186

Adjuvant treatment for phenylketonuria (PKU)

Bibliographic details: Lindegren ML, Krishnaswami S, Fonnesbeck C, Reimschisel T, Fisher J, Jackson K, Shields T, Sathe NA, McPheeters ML.  Adjuvant treatment for phenylketonuria (PKU). Rockville, MD, USA: Agency for Healthcare Research and Quality. Comparative Effectiveness Review; 56. 201222457884

Adjuvant Treatment for Phenylketonuria (PKU) [Internet]

We systematically reviewed evidence on adjuvant treatment of phenylketonuria (PKU) and evidence for a target phenylalanine (Phe) level to minimize cognitive impairment.

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Summaries for consumers

Adding the amino acid tyrosine to the diet of people with phenylketonuria

Phenylketonuria is an inherited disease. People with phenylketonuria can either not process phenylalanine from their diet at all or only in part. High blood levels of phenylalanine can cause brain or nerve damage. A diet avoiding foods high in phenylalanine can be hard to follow. People with phenylketonuria can have low levels of the amino acid tyrosine in their blood. We searched for trials which compared adding tyrosine to diet along with or instead of a phenylalanine‐restricted diet. We were able to include three trials with 56 people in the review. Although the amount of tyrosine measured in the blood of those taking the supplement was higher, there were no differences noted in any other outcome measures. There is no evidence to suggest that tyrosine should be routinely added to the diet of people with phenylketonuria. Further randomised controlled trials are needed to provide more evidence.

Using diet to manage phenylketonuria

Phenylketonuria (PKU) is an inherited disease that affects the breakdown of protein. High levels of the amino acid phenylalanine in the blood damage the nervous system and can also lead to mental handicap. Newborn babies with PKU are given a special diet low in phenylalanine. Other studies suggest that a low‐phenylalanine diet can reduce blood phenylalanine levels. The review includes four studies, but we were not able to combine many results. Results from one study showed that blood phenylalanine levels were lower and intelligent quotient higher for people on a special diet. We recommend that a low‐phenylalanine diet should be followed from the time of diagnosis. More research is needed to show if it is safe to relax this diet later on.

The impact of protein substitute on the nutrition status, growth, and neuropsychological performance of children and adults with phenylketonuria

People with phenylketonuria (PKU) who follow a low‐phenylalanine diet are required to take protein substitute to ensure adequate consumption of protein, energy, and other nutrients. The need for protein substitute has been established through clinical experience and observational data. Randomised, controlled trials are needed to confirm this need as well as its proper dosage and frequency of use. We performed a systematic review of randomised control trials investigating the impact of the use, dosage, and distribution of protein substitute on physical and neuropsychological outcomes in the treatment of PKU. Trials of children and adults diagnosed with PKU in the newborn period who were treated early and continuously were included. We planned to pool the results of the trials to estimate treatment effect. Three trials met the inclusion criteria for the review. One trial evaluated the impact of protein substitute versus no protein substitute on neuropsychological status, plasma amino acid concentrations, and nutrient intake. The remaining two trials investigated the impact of differing dosages of protein substitute on plasma amino acid concentrations and nutrient intake. No trials investigating daily protein substitute distribution were eligible for inclusion in the review. Results are presented in text form only since adequate information for data pooling was not provided. The investigators will be contacted for further information. Currently data are insufficient to reach any conclusions regarding the use, dosage, and distribution of protein substitute in the treatment of PKU. Further randomized or controlled clinical trials are needed to provide evidence for the effectiveness, dosage, and distribution of protein substitute in the treatment of PKU.

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Terms to know

Amino Acids
A chemical building block of proteins. There are 20 standard amino acids. A protein consists of a specific sequence of amino acids.
Congenital
Present since birth.
Enzymes
Protein made by the body that brings about a chemical reaction - for example, the enzymes produced by the gut to aid digestion.
Inborn Errors of Metabolism
Inborn errors of metabolism form a large class of genetic diseases. In most of the disorders, problems arise due to accumulation of substances which are toxic or interfere with normal function, or to the effects of reduced ability to synthesize essential compounds.
Metabolism
The chemical changes that take place in a cell or an organism. These changes make energy and the materials cells and organisms need to grow, reproduce, and stay healthy. Metabolism also helps get rid of toxic substances.

More about Phenylketonuria

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Also called: Phenylketonurias

Other terms to know: See all 5
Amino Acids, Congenital, Enzymes

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