LYSINE INTOLERANCE IN A VARIANT FORM OF CITRULLINEMIA

An oral loading of lysine (100 mg of lysine-HCL/kg) was performed in two patients, 18-and 23-yr-old, with a variant form of citrullinemia. Serum citrulline levels were approximately 10 times higher than control level and lysine levels were within the normal range, in contrast to the classical form of the disease in which serum citrulline is approximately 100 times normal levels and hyperlysi- nemia is usually present. After lysine loading, lysine levels rose sharply and clearance was decreased. Blood ammonia rose approximately 2.5 times. Lysine, citrulline, and arginine were markedly elevated in urine, collected 90-210 min after the lysine loading. Baseline homocitrulline and homoarginine excretion was elevated and increased further after the load. Speculation: Lysine tolerance was impaired in two patients with citrullinemia, although baseline lysine levels were normal. Lysine seemed to be catabolized along the alternate urea cycle: lysine-homocitrulline- homoarginine-urea. Hyperammpnemia was aggravated, suggesting competition between lysine and ammonia for a-ketoglutarate and inability to remove ammonia completely by these two alternate pathways. © 1979 International Pediatric Research Foundation, Inc.