A Preliminary Investigation of the Role of the Phenylalynine:Tyrosine Ratio in Children With Early and Continuously Treated Phenylketonuria: Toward Identification of “Safe” Levels

Abstract

Children with early and continuously treated phenylketonuria (ECT-PKU) remain at risk of developing executive function (EF) deficits. There is some evidence that a high phenylalanine to tyrosine ratio (phe:tyr) is more strongly associated with impaired EF development than high phenylalanine alone. This study examined EF in a sample of 11 adolescents against concurrent and historical levels of phenylalanine, phe:tyr, and tyrosine. Lifetime measures of phe:tyr were more strongly associated with EF than phenylalanine-only measures. Children with a lifetime phe:tyr less than 6 demonstrated normal EF, whereas children who had a lifetime phe:tyr above 6, on average, demonstrated clinically impaired EF.

Notes

* = sig. at p<.05

** = sig. at p<.01

# Recent phe:tyr = phe:tyr for each participant averaged over preceding year (2005)

+ Concurrent phe:tyr = average concurrent phe:tyr at 2 time periods (separated by 3 months).