Amino acid and enzyme studies of brain and other tissues in an infant with argininosuccinic aciduria.

Amino acid contents were measured in four regions of autopsied brain from an infant who presented in coma at the age of 7 weeks and died with argininosuccinic aciduria. Argininosuccinic acid lyase activity was greatly reduced in liver, kidney and cultured skin fibroblasts; incorporation of [14C]citrulline into protein by fibroblasts was minimal. Argininosuccinic acid lyase activity in brain was only slightly lower than that in control infant brain. Nevertheless, the brain showed extensive microscopic changes and a marked accumulation of argininosuccinic acid, varying between regions from 1.8 to 4.4 mmol/l. Brain contents of glutamine, glutamic acid, and alpha-amino-n-butyric acid were also greatly elevated, with a lesser elevation of citrulline, and a normal arginine content. These studies suggest genetic heterogeneity of tissue enzymes in argininosuccinic aciduria and offer some clues about pathogenesis of the neurological damage often seen in this disorder.