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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.

Results: 6

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.

Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet] - John Wiley & Sons, Ltd.

Version: 2013

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.

Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet] - John Wiley & Sons, Ltd.

Version: 2010

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.

Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet] - John Wiley & Sons, Ltd.

Version: 2015

The use of sapropterin to lower phenylalanine concentration in blood in people with phenylketonuria.

Phenylketonuria occurs due to an inherited deficiency of the enzyme phenylalanine hydroxylase. If untreated it causes an excessive accumulation of the amino acid phenylalanine in the body which prevents normal brain development. The established treatment for phenylketonuria consists of dietary restriction of natural protein but with prescribed phenylalanine‐free amino acid, mineral and vitamin supplements. With this treatment the long‐term outcome for people with phenylketonuria is excellent but the diet is onerous. Sapropterin dihydrochloride, the cofactor for phenylalanine hydroxylase, could lower phenylalanine concentration significantly in phenylketonuria and might allow a relaxation of dietary restrictions. The review identified two trials of sapropterin dihydrochloride; one in children and adults with no restricted diet and one in just children whose diet was restricted. The trials used different doses of sapropterin dihydrochloride (10 mg/kg/day and 20 mg/kg/day). We could not combine any data due to different formats of presentation. We found evidence to show that some people with mild or moderate phenylketonuria can benefit from the use of sapropterin dihydrochloride in the short term; the concentration of blood phenylalanine was lowered after treatment in both trials. The trial with the higher dose also measured the outcome change in protein tolerance. It reported an increase in protein tolerance in response to sapropterin. There were no adverse effects associated with the use of sapropterin dihydrochloride in the short term. We found no evidence on the effects of long‐term treatment. We could not draw any conclusions on its benefits in severe phenylketonuria.

Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet] - John Wiley & Sons, Ltd.

Version: 2015

Carnitine supplements for treating people with inborn errors of metabolism

Inborn errors of metabolism are genetic disorders which have a wide range of symptoms. These often start at or soon after birth but may appear first at any time during adulthood. Affected individuals may need to deal with symptoms of the disease throughout their lifetime. Symptoms are often non‐specific and may affect any organ. It can be difficult to diagnose an inborn error of metabolism. However, early detection is important and screening of infants for some disorders, such as phenylketonuria, is routine in several countries. It is recommended that carnitine supplements are prescribed in the diet of individuals with certain inborn errors of metabolism, along with other standard treatments. Carnitine supplements take the form of tablet, oral liquid, paediatric liquid and injection and might be taken with food for ease of administration. Unfortunately, we did not find any good quality trials to include in the review. This does not mean that carnitine is ineffective or should not be used in treating inborn errors of metabolism; however, individuals receiving carnitine should be carefully observed and monitored. Therefore, we recommend that clinicians base their decision to prescribe carnitine on clinical experience together with individual preferences. Future trials should include patient‐reported outcomes using validated and internationally recognised scales. Any adverse events associated with the treatment should be reported. It should be carefully considered whether placebo‐controlled trials in potentially lethal diseases, e.g. carnitine transporter disorder or glutaric aciduria type I, are ethical.

Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet] - John Wiley & Sons, Ltd.

Version: 2015

Testing Treatments: Better Research for Better Healthcare. 2nd edition

How do we know whether a particular treatment really works? How reliable is the evidence? And how do we ensure that research into medical treatments best meets the needs of patients? These are just a few of the questions addressed in a lively and informative way in Testing Treatments. Brimming with vivid examples, Testing Treatments will inspire both patients and professionals.

Pinter & Martin.

Version: 2011
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