A 6-year-old boy with hyperammonaemia: partial N-acetylglutamate synthase deficiency or portosystemic encephalopathy?
We describe a 6-year-old boy admitted with lethargy and somnolence. Laboratory tests showed hyperammonaemia (arterial level 186 micromol/l) and slightly elevated prothrombin time. The patient was treated with sodium benzoate, lactulose and a protein-restricted diet. This resulted in an insufficient decrease in blood ammonia levels. Metabolic investigations were unrevealing apart from a slightly elevated urinary glutamine concentration. Liver tissue showed steatosis and mildly decreased activity of N-acetylglutamate synthase suggesting partial deficiency. Treatment with N-carbamyl glutamate did not affect serum ammonia levels. Colour Doppler sonography and MR angiography demonstrated a patent ductus venosus. After surgical ligation of the ductus venosus, serum ammonia levels returned to normal and mental and motor performance improved markedly.


CONCLUSIONS
In late onset hyperammonaemia, partial N-acetylglutamate synthase deficiency and portocaval shunt should be ruled out.
Broere
D
D
Department of Paediatric Neurology, Academic Hospital, Free University of Amsterdam, The Netherlands. mvwegen@xs4all.nl
van Gemert
W G
WG
Kneepkens
C M
CM
Neele
D M
DM
Manoliu
R A
RA
Rauwerda
J A
JA
van der Knaap
M S
MS
D000123:Acetyltransferases / Q000172:deficiency* / Q000378:metabolism; D051046:Amino-Acid N-Acetyltransferase; D001921:Brain / Q000473:pathology; D002648:Child; D006501:Hepatic Encephalopathy / Q000150:complications / Q000175:diagnosis* / Q000601:surgery; D006801:Humans; D022124:Hyperammonemia / Q000209:etiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008661:Metabolism, Inborn Errors / Q000150:complications / Q000175:diagnosis*
D000123:Acetyltransferases; D051046:Amino-Acid N-Acetyltransferase; C494874:NAGS protein, human