Executive functioning in context: Relevance for treatment and monitoring of phenylketonuria

•Deficits in executive functioning are characteristic of early-treated PKU.•Deficits in executive functioning in PKU are related to phenylalanine-levels.•The “hot versus cool EF”-taxonomy may be relevant for PKU.•PKU-patients experience mental health problems associated with “hot” EF-deficits.

This paper presents findings from studies of EF in individuals with early-treated PKU within the context of recent advances in neuropsychological theory and research. It focuses on means of assessment, contexts of assessment, and the best way to define and investigate EF. Several conclusions can be drawn based on the findings presented here. The first conclusion is that there is clear evidence for phenylalanine-related EF-deficits in early-treated PKU, particularly with respect to prepotent response inhibition and the manipulation or monitoring component of working memory. An important note, however, is that measurement of EF in PKU has become too fragmented, as different researchers and clinicians use different definitions of EF, and subsequently, different instruments to measure EF. This appears to be one of the most important causes of mixed results.A second conclusion is that there appears to be a need to incorporate at least one specific, relatively new taxonomy of EF in PKU-research, i.e. the taxonomy that distinguishes hot and cool EFs, where hot EF is associated with regulation of affect/emotions and motivation, or regulatory functions when the context contains such elements, while cool EF concerns decontextualized regulatory abilities. PKU in adults is increasingly associated with different mental health problems, despite supposedly good treatment standards and adherence throughout childhood and adolescence. Since hot EF is strongly associated with such mental health problems, it is recommended that the hot–cool taxonomy will feature more prominently in future PKU-studies.