Speed of processing and executive functions in adults with phenylketonuria: Quick in finding the word, but not the ladybird

ABSTRACT

A reduction in processing speed is widely reported in phenylketonuria (PKU), possibly due to white matter pathology. We investigated possible deficits and their relationships with executive functions in a sample of 37 early-treated adults with PKU (AwPKUs). AwPKUs were not characterized by a generalized speed deficit, but instead their performance could be explained by two more specific impairments: (a) a deficit in the allocation of visuo-spatial attention that reduced speed in visual search tasks, in some reading conditions and visuo-motor coordination tasks; and (b) a more conservative decision mechanism that slowed down returning an answer across domains. These results suggest that the impairments in executive functions seen in AwPKUs are not the consequence of a generalized speed deficit. They also suggest that processing speed is linked to the efficiency of a particular cognitive component and cannot be considered a general function spanning domains. Similarities with patterns in ageing are discussed.

KEYWORDS:

• Phenylketonuria
• speed of processing
• executive functions
• ageing
• serial vs. parallel search
• feature vs. conjunction search

Acknowledgements

We thank Tarekegn Geberhiwot for allowing access to the patients.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 It is to be noted that AwPKUs show no deficits in tasks tapping phonological awareness—such as spoonerisms and phoneme deletion tasks—excluding an alternative account for difficulties in non-word reading (see Palermo et al., 2017).

Additional information

Funding

This research was supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme granted to Liana Palermo under the supervision of Cristina Romani (TREPAPHEN; Project ID: 329423).