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Screening & Prevention >> Newborn Screening >> Amino Acid Disorders >> PKU

PKU

Disorder Category

an amino acid (urea cycle) disorder

Screening

Finding

elevated phenylalanine

Tested By

tandem mass spectrometry (MS/MS); sensitivity=100%; specificity=99.95% [Schulze: 2003]

Names

PKU

Classic PKU

Phenylketonuria

Hyperphenylalaninemia

Phenylalanine Hydroxylase Deficiency

ICD-9

270.1, Phenylketonuria

Overview

Deficiency of phenylalanine hydroxylase (PAH), the enzyme responsible for converting ingested phenylalanine to tyrosine, results in accumulation of phenylalanine (Phe) and resulting toxic effects on brain development.

Prevalence

PKU occurs in about 1/10,000 live births in the US. [Schulze: 2003] The incidence varies greatly in other populations: Turks - 1/2,600; Irish - 1/4,500; African - 1/100,000; Japanese - 1/143,000; Finnish and Ashkenazi Jewish - 1/200,000. [PKU Review, GeneTest.org]

Inheritance

autosomal recessive

Maternal and Family History

There are variant forms with minimal symptoms (bening phenylketonuria) or intermediate symptoms (mild, variant, and Biopterin-responsive phenylketonuria). Children born to women with PKU are at risk for "maternal PKU" because high levels of phenylalanine are teratogenic.

Prenatal Testing

DNA testing by amniocentesis or CVS.

Clinical Characteristics

With treatment by early introduction and maintenance of special diet, normal IQ and development can be expected. Without treatment, symptoms in Classic PKU begin by about 6 months of age.

Initial symptoms may include:
  • a musty or "mousy" odor of the body and urine;
  • developmental delays in sitting, crawling, and standing; and
  • microcephaly.


If patients remain untreated they may develop:
  • decreased skin and hair pigmentation (due to lack of tyrosine);
  • eczema;
  • seizures; and
  • profound mental retardation.

Follow-up on positive screening test

Quantitative plasma amino acid analysis, phenylpyruvic acid in urine organic acids, red blood cell DHPR assay; urine neopterin profile; PAH mutation testing.

Primary care management

Upon notification of the + screen

If the diagnosis is confirmed

  • Educate the family regarding signs, symptoms, and the need for urgent care when the infant becomes ill (see PKU info for parents, STAR-G);
  • Support initiation and maintenance of phenylalanine-restricted diet and supplementation of tyrosine and essential amino acids;
  • Avoiding the sugar substitute aspartame ("Nutrasweet", "Equal", "Sweetmate", Canderal") in diet drinks and medications;
  • Regular blood and urine tests to monitor Phe levels and diet may be indicated;
  • For those identified after irreversible consequences, assist in management, particularly with developmental and educational interventions.

Specialty Care Management

Initial consultation and ongoing collaboration if the child is affected. A dietician may work with the family to devise an optimal approach to dietary management.

Resources

Links

For Professionals

PKU info for professionals, STAR-G
On the Screening, Technology and Research in Genetics (STAR-G) site, one of a series of Disorder Fact Sheets for Professionals; structured list of information about the condition, with links to more information.

ACT Sheet for PKU from ACMG (pdf 120kb)
Developed by the American College of Medical Genetics (ACMG), includes recommended responses to positive newborn screening test results, diagnostic evaluation, clinical expectations, and sources of additional information. See the ACMG ACT Sheets and Confirmatory Algorithms (link elsewhere on this page) for more info and sheets on other conditions.

ACMG ACT Sheets and Confirmatory Algorithms
The American College of Medical Genetics (ACMG) has developed ACTion (ACT) Sheets and algorithms for responding to positive newborn screening test results. This page contains a table with links to all of the ACT Sheets and related algorithms.

PKU Review, GeneTest.org
Excellent review by John J. Mitchell, MD and Charles R. Scriver, MD including clinical description, differential, management, genetic counseling, molecular genetics, and a bibliography.

Utah Newborn Screening Program
The site provides information and statistics about the program and related legislation, training for practices, and the conditions screened for.

For Parents

PKU info for parents, STAR-G
From the Screening, Technology and Research in Genetics (STAR-G) site, providing information for parents about PKU and links to other sites including parent support groups.

PKU, Genetics Home Reference
Excellent, detailed review aimed at patients and families from the National Library of Medicine's Genetics Home Reference site.

National Urea Cycle Disorders Foundation
The National Urea Cycle Disorders Foundation, a non-profit organization, provides support services and information for families; medical lectures on urea cycle disorders; nutrition and medication resources; and information about events and conferences.

Services

Newborn Screening Programs

Utah Newborn Screening Program, more info...
44 Mario Capecchi Drive
Salt Lake City, UT84114
Phone: 801-584-8256
Fax: 801-536-0966
http://health.utah.gov/newbornscreening

Pediatric Genetics

Metabolic Clinic, more info...
100 Mario Capecchi Drive
Salt Lake City, UT84113
Phone: 801-585-2457
Fax: 585-7252
http://www.ped.med.utah.edu/divisions/divisions.htm

See all Pediatric Genetics services providers (3) in our database.

For other services related to this condition, browse our Services categories or search our database.

Helpful Articles

PubMed search for review articles on PKU in the last 5 years.

Authors

Compiled and edited by: Alfred Romeo RN, PhD, 3/2007
Content Last Updated: 3/2008

Page Bibliography

Schulze A, Lindner M, Kohlmuller D, Olgemoller K, Mayatepek E, Hoffmann GF.
Expanded newborn screening for inborn errors of metabolism by electrospray ionization-tandem mass spectrometry: results, outcome, and implications.
Pediatrics. 2003;111(6 Pt 1):1399-406. PubMed abstract
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