Carbamyl phosphate synthetase I is a urea cycle enzyme. Severe deficiency o
f carbamyl phosphate synthetase I presents in the neonatal period as hypera
mmonemic encephalopathy with altered consciousness and occasional seizures
after feeding begins. Episodes of altered consciousness with or without sei
zures and focal neurologic deficits are seen later with patients of partial
carbamyl phosphate synthetase I deficiency. Fatal cerebral edema with brai
n herniation may develop on occasion. Three patients presenting with carbam
yl phosphate synthetase I deficiency are reported with neuroimaging and pat
hologic findings illustrating the destructive encephalopathy with acute cer
ebral edema, followed by diffuse cerebral atrophy and occasional cystic enc
ephalomalacia. The deterioration in carbamyl phosphate synthetase I deficie
ncy occurs during the hyperammonemic crises. This deficiency may be difficu
lt to treat despite the current advances in treatment strategies, especiall
y in neonatal-onset patients with low carbamyl phosphate synthetase I activ
ity. (C) 2001 by Elsevier Science Inc. All rights reserved.