Serum Guanidinosuccinic Acid Levels In Urea Cycle Diseases

Guanidinosuccinic acid (GSA) was first isolated from urine of uremic patients and identified by Natelson et al. in 19641. Two pathways have been proposed for the biosynthesis. In 1968 Cohen suggested that GSA would be formed by transamidination of arginine to aspartic acid2. A second hypothesis, proposed by Natelson and Sherwin suggested that GSA could be synthesized as an inert overflow product through the guanidine cycle. The guanidine cycle is an alternate cycle proposed for the conversion of urea nitrogen to creatine3.