Cognitive outcomes in early-treated adults with phenylketonuria (PKU): a comprehensive picture across domains

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

Research output: Contribution to journalArticlepeer-review


OBJECTIVE: Phenylketonuria (PKU) is an inherited metabolic disease which affects cognitive functions due to an inability to metabolize phenylalanine which leads to the accumulation of toxic by-products (Phe) in the brain. PKU can be effectively treated with a low phenylalanine diet, but some cognitive deficits remain. Studies have reported impairments, especially for processing speed and executive functions, but there is a lack of comprehensive assessment across cognitive domains. Moreover, it is important to establish outcomes in early treated adults with PKU (AwPKU) who have better metabolic control than groups previously reported in the literature.

METHOD: We tested 37 AwPKU with an unprecedented number of tasks (N = 28) and measures (N = 44) and compared results with 30 controls matched for age and education.

RESULTS: We found (a) group impairments, particularly in tasks tapping speed of processing and complex executive functions; (b) high variability across participants, with a sizable number of AwPKU with completely normal performance (about 38%); (c) but also a sizable number of participants who were clearly impaired (about 24%); and (d) good performance in tasks tapping verbal learning, verbal memory and orthographic processing, indicating no generalized learning impairment.

CONCLUSION: Our results indicate good outcomes, but also that deficits are still present with current treatment policies. (PsycINFO Database Record

Original languageEnglish
Pages (from-to)255–267
Number of pages13
Issue number3
Publication statusPublished - 12 Jan 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.

Supplemental materials:


  • adult PKU
  • metabolic diseases
  • cognitive impairments
  • executive functions and speed of processing
  • memory and learning


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