The prefrontal cortex of the brain has been shown to play a
crucial role in working memory, and age-related changes in
prefrontal function may contribute to the improvements in working
memory that are observed during childhood. We examined the
developmental trajectory of working memory in school-age children
with early-treated phenylketonuria (PKU), a metabolic disorder
that results in prefrontal dysfunction. Using a recognition
procedure, we evaluated working memory for letters, abstract
objects, and spatial locations in 20 children with PKU and 20
typically developing control children. Children in both groups
ranged from 6 to 17 years of age. Our findings revealed poorer
performance across all three types of materials for children
with PKU. In addition, there was a significant difference in
the developmental trajectory of working memory for children
with PKU as compared with controls. Specifically, deficits were
not apparent in younger children with PKU. Instead, deficits
were observed only in older children, suggesting the presence
of a developmental deficit rather than a developmental delay
in the working memory of children with PKU. (JINS,
2002, 8, 1–11.)