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Non-PKU mild hyperphenylalaninemia (MHP)--the dilemma

W B Hanley1

  • 1Division of Clinical Genetics, Department of Paediatrics, The Hospital for Sick Children, 555 University Ave, Toronto, ON, M5G 1X8, Canada. whanley@pathcom.com

Molecular Genetics and Metabolism
|June 3, 2011
PubMed

Insights

Mild hyperphenylalaninemia (MHP) patients may not benefit from treatments like tetrahydrobiopterin (BH4) or low phenylalanine diets. Current evidence does not support treating MHP, unlike phenylketonuria (PKU).

Area of Science:

  • Metabolic Disorders
  • Neurodevelopmental Disorders
  • Genetics

Background:

  • Recent reviews suggest potential neuropsychological deficits in non-PKU mild hyperphenylalaninemia (MHP) patients, prompting consideration for treatments like tetrahydrobiopterin (BH4) or low phenylalanine (Phe) diets.
  • Phenylketonuria (PKU) patients, including Classical and Mild/Atypical variants, typically require mean lifetime Phe levels of 120-360 μmol/L for optimal outcomes.
  • MHP patients naturally exhibit Phe levels between 200-600 μmol/L, a condition previously considered benign.

Purpose of the Study:

  • To critically review the available literature regarding the potential benefits of treating MHP patients.
  • To evaluate the evidence supporting neuropsychological benefits of BH4 and/or Phe-restricted diets in MHP.
  • To advocate for a unified global classification system for PKU phenotypes.

Main Methods:

  • Comprehensive literature review of existing studies on MHP and PKU.
  • Analysis of Phe levels and treatment outcomes in PKU and MHP patient populations.
  • Assessment of evidence for executive function deficits in MHP.

Main Results:

  • The literature review uncovered no substantial evidence to support the treatment of MHP with BH4 or Phe-restricted diets.
  • Optimal Phe levels for PKU management differ significantly from natural Phe levels observed in MHP.
  • The benign nature of MHP requires further investigation with more subject testing.

Conclusions:

  • Current evidence does not support the therapeutic intervention for MHP, contrasting with PKU management strategies.
  • Further research and testing in MHP subjects are necessary to confirm these findings.
  • A standardized international classification for PKU phenotypes is needed.

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