Date of Award

Summer 8-2017

Author's School

Graduate School of Arts and Sciences

Author's Department


Degree Name

Master of Arts (AM/MA)

Degree Type



Phenylketonuria (PKU) is a recessive disorder characterized by disruption in the metabolism of the amino acid phenylalanine. Using a verbal fluency task, previous studies demonstrated that word production is reduced in individuals with PKU relative to controls. Beyond word production, verbal fluency output can be scored for clustering and switching, which enable characterization of verbal and executive processes, respectively. The present study is the first to evaluate clustering and switching in PKU within a longitudinal design, thereby elucidating the developmental time course of core cognitive processes. To this end, semantic (animals, food/drink) and phonemic (S words, F words) fluency data were obtained at three longitudinal time-points in children with early- and continuously-treated PKU (n = 23; 11 males, 12 females) and age-matched controls (n = 44; 22 males, 22 females). Age ranged from 7-19 years at the outset of the study; approximately 12-18 months elapsed between each time-point. Word production, clustering, and switching scores were analyzed using hierarchical linear modeling (HLM) to account for longitudinal dependencies and to allow evaluation of the individual contributions of age, group, and the interaction between age and group. Results indicated impairments in frontally-mediated executive processes in children with PKU relative to controls, and these impairments were exacerbated with increasing age. Additionally, children with PKU relied more on verbal processes relative to controls, suggesting that they may use compensatory strategies to overcome executive deficits. Continued efforts to characterize cognitive development in children with PKU will inform our understanding of the disorder across the lifespan.


English (en)

Chair and Committee

Desirée White

Committee Members

Denise Head, Janet Duchek


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