Effects of dietary management of phenylketonuria on long- term cognitive outcome

Shelley Channon ¹, Galya Goodman ¹, Sally Zlotowitz ¹, Caroline Mockler ¹ and Philip J Lee ^1*

¹ UCL, United Kingdom

^* To whom correspondence should be addressed. E-mail: philip.lee{at}uclh.nhs.uk.

Accepted 13 October 2006

Abstract

Background and aims: Phenylketonuria (PKU) is associated with dopaminergic depletion in the dorsolateral prefrontal cortex and abnormalities of myelination. Both mechanisms may lead to deficits in cognitive functioning. Studies of cognitive outcome in early-treated children with PKU have suggested there are benefits in remaining on diet into adolescence. This study was designed to assess the nature and extent of any cognitive deficits in early-treated adults who discontinued diet in adolescence.

Method: We compared 25 patients (aged 18-38 years) who were early-diagnosed and discontinued diet in adolescence with 25 adults (aged 18-38 years) with PKU on continuous diet and with a healthy control group (n=45).

Results: The groups differed significantly on accuracy (p=.007) and speed (p=.001) of performance on an n-back working memory task and on speed of performance (p=.001) on a flanker inhibitory task, but not on flanker accuracy, object alternation learning or perceptual judgment tasks (all p>.05). The off-diet group performed significantly below the on-diet group on n-back accuracy (p=.007) and flanker speed (p=.05), and significantly below the healthy control group on n-back speed (p=.002) and flanker speed (p=.0001).

Conclusion: The findings suggest that although discontinuing diet in adolescence appears disadvantageous compared to remaining on continuous diet, any deficits are relatively subtle.

Keywords: adulthood, diet therapy, neuropsychometry, outcome, phenylketonuria

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