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Phenylketonuria (PKU) is a protein metabolism disorder characterized by high blood levels of the amino acid phenylalanine. This results from a mutation in the gene responsible for phenylalanine hydroxylase, an enzyme that converts phenylalanine into tyrosine. When this enzyme is deficient, phenylalanine builds up in the blood, leading to symptoms such as vomiting, rashes, seizures, growth deficiency, and severe mental retardation. An early diagnosis and a diet restricting phenylalanine intake...
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Phenylalanine hydroxylase deficiency.

John J Mitchell1, Yannis J Trakadis, Charles R Scriver

  • 1Department of Medical Genetics, McGill University Health Center, Montreal, Canada. john.mitchell@muhc.mcgill.ca

Genetics in Medicine : Official Journal of the American College of Medical Genetics
|May 11, 2011
PubMed
Summary
This summary is machine-generated.

Phenylalanine hydroxylase deficiency, a genetic disorder, causes intolerance to phenylalanine. Early diagnosis via newborn screening and lifelong dietary management enable affected individuals to lead normal lives.

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Area of Science:

  • Biochemistry
  • Genetics
  • Pediatrics

Background:

  • Phenylalanine hydroxylase (PAH) deficiency is an autosomal recessive disorder affecting approximately 1 in 15,000 individuals.
  • It leads to intolerance of dietary phenylalanine, causing a spectrum of conditions from classic phenylketonuria (PKU) to mild hyperphenylalaninemia.
  • Untreated classic PKU results in severe, irreversible intellectual disability.

Purpose of the Study:

  • To review the diagnosis, management, and ongoing challenges of phenylalanine hydroxylase deficiency.
  • To highlight the impact of newborn screening and current therapeutic strategies.
  • To address specific considerations for pregnant women and the potential benefits of adjuvant therapies.

Main Methods:

  • Newborn screening using blood spot assays to detect hyperphenylalaninemia.
  • Lifelong dietary management including low-protein diets and phenylalanine-free medical formulas.
  • Monitoring of plasma phenylalanine and tyrosine levels.
  • Consideration of adjuvant therapy with 6R-tetrahydrobiopterin.
  • Genetic testing for carrier status and prenatal diagnosis.

Main Results:

  • Newborn screening has significantly reduced the major neurologic consequences of hyperphenylalaninemia.
  • Affected individuals can achieve normal lives with early and consistent treatment.
  • Despite treatment, some individuals experience neuropsychological issues, indicating incomplete homeostasis restoration.
  • Specific phenylalanine targets are crucial for optimal outcomes, particularly in early life.

Conclusions:

  • Phenylalanine hydroxylase deficiency requires lifelong management, emphasizing early diagnosis and adherence to dietary restrictions.
  • While current therapies are effective, further research is needed to address residual neuropsychological challenges.
  • Specialized guidelines are essential for pregnant women with PAH deficiency due to teratogenic risks.
  • Adjuvant therapies and genetic testing play important roles in comprehensive patient care.