Guanidinoacetate and creatine plus creatinine assessment in physiologic fluids: An effective diagnostic tool for the biochemical diagnosis of arginine:glycine amidinotransferase and guanidinoacetate methyltransferase deficiencies

Background: Disorders of creatine metabolism arise from genetic alterations of arginine:glycine amidinotransferase (AGAT), guanidinoacetate methyltransferase (GAMT), and the creatine transporter. We developed a strategy for the detection of AGAT and GAMT defects by measurement of guanidinoacetate (GAA) and creatine plus creatinine (Cr+Crn) in biological fluids. Methods: Three patients with AGAT deficiency from the same pedigree and their eight relatives, as well as a patient affected by a GAMT defect and his parents were analyzed by a new HPLC procedure in comparison with 90 controls. The method, which uses precolumn derivatization with benzoin, separation with a reversed-phase column, and fluorescence detection, has shown good precision and sensitivity and requires minimal sample handling. Results: In the three AGAT patients, plasma GAA was 0.01-0.04 μmol/L [mean (SD) for neurologically normal controls was 1.16 (0.59) μmol/L], Cr+Crn was 15-29 μmol/L [reference limit in our laboratory, 79 (38) μmol/L]. Urinary GAA was 2.4-5.8 μmol/L [reference, 311 (191) μmol/L], and Cr+Crn was 2.1-3.3 mmol/L [reference, 9.9 (4.1) mmol/L]. We found a smaller decrease in GAA and Cr+Crn in some carriers of an AGAT defect. In the patient with GAMT deficiency, plasma and urine GAA was increased (18.6 and 1783 μmol/L, respectively), and Cr+Crn was decreased in plasma (10.7 μmol/L) and urine (2.1 mmol/L). GAA was increased in the parents' plasmas and in the mother's urine. Conclusion: The assessment of GAA is a new tool for the detection of both GAMT and AGAT deficiencies.