Liver ultrastructure in mitochondrial urea cycle enzyme deficiencies and comparison with Reye's syndrome.

The liver ultrastructural findings in two girls with partial carbamyl phosphate synthetase I (CPS) deficiency and their heterozygote parents and two siblings with ornithine transcarbamylase (OTC) deficiency are described. Liver ultrastructure in the four patients with inherited deficiencies of urea cycle enzymes showed minimal alterations with essentially normal mitochondria when biopsy was performed during periods of good control of their hyperammonemia. Mitochondrial ultrastructure was also essentially normal in the heterozygotes for carbamyl phosphate synthetase I deficiency. These findings are in contrast to the marked alterations in mitochondrial ultrastructure found in the study of two cases of Reye's syndrome in which severe depression of ornithine transcarbamylase and carbamyl phosphate synthetase I activities was noted.