Periodic attacks of lethargy in a baby with ammonia intoxication due to a congenital defect in ureogenesis.

Hyperammonaemia due to a deficient urea cycle (Fig. 1) has been attributed to at least four distinct enzyme defects: (1) hyperanmmonaemia due to a defect of carbamyl-phosphate synthetase L. the liver (Freeman et al., 1964); (2) hyperammonaemia due to a defect of ornithine carbamyl transferase with or without defect of carbamyl phosphate synthetase in the liver (Russell et al., 1962; Hopkins et al., 1969; Levin et al., 1969a; Levin et al., 1969b); (3) citrullinaemia due to a defect of argininosuccinic acid synthetase in the liver (McMurray et al., 1964) and in fibroblast cultures (Tedesco and Mellman, 1967); and