Children and adolescents with phenylketonuria (PKU) have more extensive deficits in executive function — a set of cognitive skills that help in setting goals and getting things done in daily life – than those with autism spectrum disorder (ASD), a study has found.
Yet, those with PKU do not exhibit problems in adaptive and emotional behaviors as ASD patients do, suggesting that such behavioral difficulties are not dependent on executive function deficits.
The research also indicates that comparing neurodevelopmental disorders may help understand the nature of disease-specific behaviors.
The study, “Executive functioning, adaptive skills, emotional and behavioral profile: A comparison between autism spectrum disorder and phenylketonuria,” was published in the journal Molecular Genetics and Metabolism Reports.
People with ASD have persistent problems in communicating and interacting socially, and exhibit repetitive patterns of behavior.
These patients are known to have deficits in executive functions regulating goal-directed behaviors. However, it is not clear whether such cognitive deficits are the cause of other disease features, such as problems adapting to distinct environments, difficulty regulating or expressing emotions, or outbursts in response to external triggers.
To learn more, a team at Sapienza University of Rome, in Italy, compared deficits in executive function, as well as adaptive, emotional and behavior problems in young people with ASD to those with PKU, who also have deficits in executive function.
“If behavioral and emotional difficulties present in ASD originate, at least partially, from EF [executive function] deficits, we would expect that clinical groups with comparable EF deficient profiles should present similar behavioral and emotional patterns,” the team wrote.
Researchers examined data from 21 ASD patients without intellectual disability, 15 PKU patients on a phenylalanine restricted diet since early in life, and 14 controls recruited from city schools. All participants were age 7 to 14 years, and had similar IQ scores.
Each participant underwent a set of tests assessing three main domains of executive function: working memory, which refers to the ability to maintain and manipulate information; response inhibition, or self-control; and cognitive flexibility, which refers to the ability to adapt to new demands or needs.
Their parents also filled questionnaires assessing emotional and behavioral problems, as well as adaptive behaviors in these children and adolescents.
Results showed that ASD patients exhibited impaired cognitive flexibility compared with controls. But the extent of executive function deficits was greater in PKU patients, who had impairments in both cognitive flexibility and response inhibition compared with the control group.
Regarding behavior, children and adolescents with ASD had more emotional problems — which can include depression, social withdrawal, and anxiety — than controls or PKU patients. They also had higher scores in total problems, which quantifies the overall extent of both emotional and behavioral problems.
General and social adaptive skills also were worse in ASD patients compared with both PKU children and controls.
Overall, the findings confirm the presence of executive function impairments in both ASD and PKU patients, as well as general difficulties in adaptive and emotional functioning in those with ASD.
While executive function plays a critical role in the development of adaptive and emotional domains, the results suggest that deficits in executive function alone cannot explain the behavioral problems experienced by people with ASD.
“These results support a relative independence of adaptive and emotional behavioral difficulties from difficulties of executive functions and suggest that other dysfunctions might contribute to the multidimensional phenotype of individuals with ASD,” the researchers wrote.
“Comparisons of the commonalities and differences between EF deficits in different clinical conditions can allow greater understanding of the neuropsychology of the single disorders,” they concluded.