Dietary interventions for phenylketonuria (Cochrane Review)

A substantive amendment to this systematic review was last made on 04 May 1999. Cochrane reviews are regularly checked and updated if necessary.

Background: Phenylketonuria is an inherited disease treated with dietary restriction of the amino acid phenylalanine. The diet is initiated in the neonatal period to prevent mental handicap however it is restrictive and can be difficult to follow. Whether the diet can be relaxed or discontinued during adolescence or should be continued for life remains a controversial issue which we aim to address in this review.

Objectives: To assess the effects of a low-phenylalanine diet commenced early in life for people with phenylketonuria. To assess the possible effects of relaxation or termination of the diet on intelligence, neuropsychological outcomes and mortality, growth, nutritional status, eating behaviour and quality of life.

Search strategy: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and abstract books of conference proceedings. Most recent search of the Group's trials register: October 2002.

Selection criteria: All randomised or quasi-randomised controlled trials comparing a low-phenylalanine diet to relaxation or termination of dietary restrictions in people with phenylketonuria.

Data collection and analysis: Two reviewers independently assessed study eligibility and methodological quality and extracted the data.

Main results: Four studies were included in this review (251 participants). Few significant differences were found between treatment and comparison groups for the outcomes of interest. Blood phenylalanine levels were significantly lower in subjects with phenylketonuria following a low-phenylalanine diet compared to those on a less restricted diet (weighted mean difference (WMD) at three months -672.20, 95% confidence interval (CI) -813.80 to -530.61). Intelligence quotient was significantly higher in subjects who continued the diet than in those who stopped the diet (WMD after 12 months -5.00 (95% CI -9.60 to -0.40)). However, these results came from only one study.

Reviewers' conclusions: The results of non-randomised studies have concluded that a low-phenylalanine diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcome. No randomised controlled studies have assessed the effect of a low-phenylalanine diet versus no diet from diagnosis. In view of evidence from non-randomised studies, such a study would be unethical and it is recommended that low-phenylalanine diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. This should be addressed by randomised controlled studies.

Citation: Poustie VJ, Rutherford P. Dietary interventions for phenylketonuria (Cochrane Review). In: The Cochrane Library, Issue 3, 2003. Oxford: Update Software.

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This is an abstract of a regularly updated, systematic review prepared and maintained by the Cochrane Collaboration. The full text of the review is available in The Cochrane Library (ISSN 1464-780X).

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