MIZUTANI, N., HAYAKAWA, C., OHYA, Y., WATANABE, K., WATANABE, Y. and MORI, A. Guanidino Compounds in Hyperargininemia. Tohoku J. exp. Med., 1987, 153 (3), 197-205 - Plasma and cerebrospinal fluid (CSF) concentrations and urinary excretion of guanidino compounds were investigated in a patient with hyperargininemia during the treatment with low-protein diet, oral administration of an essential amino acid mixture and sodium benzoate, or enzyme replacement therapy such as exchange transfusion or erythrocyte transfusion. In the patient, α-keto-δ-guanidinovaleric acid (GVA), N-α-acetylarginine (NAA), argininic acid (ArgA) and homoarginine concentrations in plasma were elevated as well as arginine. Urinary excretion of GVA, ArgA, NAA and γ-guanidinobutyric acid (GBA) were also increased. CSF concentrations of ArgA, homoarginine and arginine were also elevated. On the other hand, guanidinosuccinic acid (GSA), which is usually detected in all samples, was not detected in plasma, CSF and urine of the patient. The present results suggest that in patients with hyperargininemia other factors such as arginine and its metabolites including GVA, GAA, ArgA and homoarginine may cause the neurological symptoms. Furthermore, it is suggested that in patients with hyperargininemia, arginine may be catabolized via other pathways and nitrogen may be excreted partially in urine in the form of some of guanidino compounds.