N-Acetylglutamate Synthetase Deficiency Workup

Updated: Feb 18, 2019
  • Author: Karl S Roth, MD; Chief Editor: Luis O Rohena, MD, PhD, FAAP, FACMG  more...
  • Print

Laboratory Studies

Affected newborns may experience fulminant hyperammonemia, which remains undetected unless index of suspicion is high.

No routine laboratory tests provide definitive clues. The BUN level may be low, but this is an unreliable index of high blood ammonia. A respiratory alkalosis may be present. Urine orotic acid levels are within reference ranges.

Plasma alanine and glutamine levels are elevated.

Urine amino acids are nondiagnostic in N- acetylglutamate synthetase (NAGS) deficiency but are important in order to help rule out hyperammonemia-hyperornithinemia-homocitrullinuria (HHH) or lysinuric protein intolerance (LPI) (see Differentials).

Urine organic acids are within reference ranges in NAGS deficiency. Ruling out organic acid disorders, which can present with similar signs and symptoms and hyperammonemia, is important.

Definitive diagnosis rests with DNA sequencing; to date, there is no newborn metabolic screen which can detect the defect.


Imaging Studies

Imaging studies generally are not helpful, with the exception of brain imaging when cerebral edema is suspected. Documenting a finding of cerebral edema is important.



DNA sequencing is available in selected laboratories; mutation analysis provides a definitive diagnosis