The impact of phenylalanine levels on cognitive outcomes in adults with phenylketonuria: effects across tasks and developmental stages

Cristina Romani*, Liana Palermo, Anita MacDonald, Ellie Limback, S. Kate Hall, Tarekegn Geberhiwot

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


OBJECTIVE: Phenylketonuria (PKU) is due to an inability to metabolize the amino acid phenylalanine (Phe), leading to its accumulation in the brain. Phe levels can be controlled following a protein-free diet, but cognitive impairments are still present. A number of questions remain to be answered related to which type of metabolic control is important, the age when it is important, the cognitive functions which are most affected and, the best tests to use to monitor cognitive health.

METHOD: We investigated the impact of metabolic control at different ages on cognitive performance in 37 early treated adults with PKU.

RESULTS: (a) Phe variation was as associated to performance as average Phe showing that stable dietary control is as important as strict control; (b) For some tasks, current and adult Phe were stronger predictors of performance than childhood or adolescent Phe, showing the importance of a strict diet even in adulthood; and (c) The relationship between performance and Phe levels varied depending on time and cognitive domain. For some functions (sustained attention, visuomotor coordination), Phe at the time of testing was the best predictor. While for other functions (visual attention, executive functions) there was a diminishing or stable relationship across time.

CONCLUSION: Results show the importance of selecting the right tasks to monitor outcomes across ages, but also that the impact of bio-chemical disruptions is different for different functions, at different ages. We show how inherited metabolic diseases offer us a unique vantage point to inform our understanding of brain development and functioning. (PsycINFO Database Record

Original languageEnglish
Pages (from-to)242-254
Number of pages13
Issue number3
Publication statusPublished - 1 Mar 2017

Bibliographical note

This article has been published under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Copyright for this article is retained by the author(s). Author(s) grant(s) the American Psychological Association the exclusive right to publish the article and identify itself as the original publisher.


  • cognitive skills
  • development
  • memory and learning
  • phenylalanine fluctuations
  • PKU


Dive into the research topics of 'The impact of phenylalanine levels on cognitive outcomes in adults with phenylketonuria: effects across tasks and developmental stages'. Together they form a unique fingerprint.

Cite this