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[Increased phenylalanine]

Phenylketonuria (PKU)


Differential Diagnosis: Phenylketonuria (Classical PKU); non-PKU mild hyperphenylalaninemia; ptern defects; transient hyperphenylalaninemia. 

Condition Description: In PKU the phenylalanine from ingested protein cannot be metabolized to tyrosine because of a deficient liver phenylalanine hydroxylase (PHA). This causes elevated phenylalanine. Ptern defects result from deficiency of tetrahydrobiopterin (BH4), the cofactor for PAH and other hydroxylases. This produces not only increased phenylalanine, but also neurotransmitter deficiencies. 

You Should Take the Following IMMEDIATE Actions:

  • Contact family immediately to inform them of the newborn screening result
  • Consult pediatric metabolic specialist
  • Evaluate infant and refer as appropriate
  • Initiate confirmatory/diagnostic tests in consultation with metabolic specialist
  • Provide the family with basic information about PKU and dietary management
  • Report findings to state newborn screening program (Carleigh Soule at 307-777-6297) 

Diagnostic Evaluation: Plasma amino acid analysis which shows increase phenylalanine without increased tyrosine (increased phenylalanine: tyrosine ratio). Urine pterin analysis and red blood cell DHPR assay will identify pterin defects. Consider PAH mutation testing.  

Clinical Considerations:   Asymptomatic in the neonate. If untreated, PKU will cause irreversible mental retardation, hyperactivity, autistic-like features, and seizures. Treatment will usually prevent these symptoms. Pterin defects cause early severe neurological damage (developmental delay/seizures) and require specific therapy. 

Additional Information: (Click on the name to take you to the website) 

Genetic Home Reference                                            Wyoming Department of Health                                        

New England Metabolic Consortium                               Colorado Newborn Screening                            

Gene Tests – Gene Clinics                                            American Academy of Pediatrics                                


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