Beyond executive function: Non-executive cognitive abilities in individuals with PKU

Individuals with early-treated phenylketonuria (ETPKU) most often present with impairment in executive function (EF) and average intelligence compared to the general population. The topic of this review, which is less often discussed, is non-EF impairments that may be associated with ETPKU. Studies that have included assessment of non-EF cognitive functions such as information processing speed, fine motor skills, and perception and visual–spatial abilities suggest that individuals with ETPKU are compromised in these areas. Those assessing non-EF cognitive functions of language skills, long-term memory, and learning skills have yielded mixed results, with some suggesting impairment and others suggesting intact abilities. Although more studies are required, research to date suggests that mechanisms for non-EF deficits may include prefrontal cortex dopamine deficiency and/or white matter abnormalities related to elevated blood phenylalanine levels. For individuals with ETPKU to reach their full potential in life, it is vital to address the challenges associated with EF and non-EF deficits by identifying impairments and appropriate treatment strategies.