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Published on: June 25, 2010

Metabolic phenotypes of phenylketonuria. Kinetic and molecular evaluation of the Blaskovics protein loading test

U Langenbeck1, P Burgard, U Wendel

  • 1Institute of Human Genetics, Frankfurt University Hospital, Frankfurt/Main, Germany. ulrich.langenbeck@gmx.net

Journal of Inherited Metabolic Disease
|July 18, 2009
PubMed

Insights

Phenylalanine (Phe) metabolism in infants with phenylketonuria (PKU) was studied using a kinetic model. The intermediate Phe response type shows accelerated disposal, with significant variability despite identical PAH genotypes.

Area of Science:

  • Biochemistry
  • Genetics
  • Pediatrics

Background:

  • Phenylketonuria (PKU) is a metabolic disorder affecting phenylalanine (Phe) metabolism.
  • A German study classified infant Phe responses into three types.
  • Type II represents mild PKU with specific blood Phe level dynamics.

Purpose of the Study:

  • To classify and characterize the intermediate Phe response kinetically and molecularly.
  • To estimate the phenotypic variability in Phe disposal.
  • To understand the biochemical basis of mild PKU.

Main Methods:

  • Applied a kinetic model (zero-order protein synthesis, first-order Phe disposal) to 157 protein loading tests.
  • Analyzed blood Phe levels over three days in infants at 6 months of age.
  • Correlated kinetic data with specific PAH genotypes.

Main Results:

  • An exponentially saturated activation model described accelerated Phe disposal in the intermediate type.
  • Eleven p.Y414C hemizygotes and two p.R261Q homozygotes showed this kinetic type.
  • Phe metabolic disposal rates varied widely but correlated with 72-hour Phe levels.

Conclusions:

  • The intermediate Phe response involves accelerated disposal, suggesting adaptive mechanisms.
  • Phenotypic variability in Phe disposal exists even with identical PAH genotypes.
  • Kinetic modeling provides insights into PKU pathophysiology and genotype-phenotype correlations.
Abstract

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