N-acetylglutamate synthase (
NAGS) deficiency is a rare
urea cycle disorder. An effective treatment, N-carbamoyl-
L-glutamic acid (
NCGA), is now available, increasing the importance of identifying and treating these patients early. We describe a case with genetically verified
NAGS deficiency and neonatal onset of severe hyperammonaemia. The
ammonia levels increased above 1400 micromol/L. The patient did not respond to
NCGA treatment during the first 15 h, indicating that a delayed response or no response cannot be used as a safe
indicator for excluding
NAGS deficiency in the acute situation. Hence, conventional treatment should not be delayed by a diagnostic procedure, such as a loading test. Furthermore, at 3 years of age this patient has normal psychomotor development, underlining the possibility of a favourable outcome despite markedly elevated
ammonia levels,
coma, and
seizures in the neonatal period. Including
NCGA early in the treatment of patients with hyperammonaemia may be of clinical importance. In order to detect patients with
NAGS deficiency and neonatal onset and to optimize care, it is important to use the available treatment strategies to reduce plasma
ammonia concentrations without delay. We propose the use of combined symptomatic treatment, i.e.
glucose infusion,
sodium benzoate,
arginine or
citrulline, and when indicated haemodialysis, as well as
NCGA treatment in all neonates presenting with severe hyperammonaemia. The treatment should be continued until laboratory investigations are complete or indicate another disorder.