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[Increased leucine]       

Maple Syrup Urine Disease (MSUD)


Differential Diagnosis: Maple syrup urine disease (MSUD); hydroxyprolinemia. 

Condition Description: In MSUD, leucine, isoleucine, and valine (branched chain amino acids) can not be metabolized further than their α-ketoacid derivatives. The amino acids and organic acids accumulate and produce severe toxicity. 


  • Contact family to inform them of the newborn screening result and ascertain clinical status (poor feeding, vomiting, lethargy, tachypnea)
  • Consult with pediatric metabolic specialist
  • Evaluate the newborn (poor feeding, lethargy, tachypnea, alternating hypertonia/hypotonia, seizures) If any sign is present or infant is ill, transport to hospital for further treatment in consultation with metabolic specialist
  • Initiate timely confirmatory/diagnostic testing and management, as recommended by specialist
  • Provide the family with basic information about MSUD and dietary management
  • Report findings to state newborn screening program (Carleigh Soule at 307-777-6297)  

Diagnostic Evaluation: In MSUD, plasma amino acid analysis reveals elevations of leucine, isoleucine, alloleucine, and valine (the branched chain amino acids) and urine organic acid analysis reveals abnormal branched chain hydroxyl- and ketoacids. In expanded screening, leucine/isoleucine and hydroxyproline can not be differentiated, so if the baby has hydroxyprolinemia confirmatory amino acid analysis will show only increased hydroxyproline. 

Clinical Expectations: MSUD presents in the neonate with feeding intolerance, failure to thrive, vomiting, lethargy and maple syrup odor to urine and cerumen. If untreated, it will progress irreversible mental retardation, hyperactivity, failure to thrive, seizures, coma, cerebral edema, and possible death. Hydroxyprolinemia is probably benign. 

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

Genetic Home Reference                                   Wyoming Department of Health                               

Gene Tests – Gene Clinics                                  Colorado Newborn Screening                       

New England Consortium                                    American Academy of Pediatrics              


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