Automated high-performance liquid chromatographic method for the determination of guanidinoacetic acid in dried blood spots: a tool for early diagnosis of guanidinoacetate methyltransferase deficiency

Dietary glycine supplementation enhances syntheses of creatine and glutathione by tissues of hybrid striped bass (Morone saxatilis ♀ × Morone chrysops ♂) fed soybean meal-based diets

BACKGROUND

We recently reported that supplementing glycine to soybean meal-based diets is necessary for the optimum growth of 5- to 40-g (Phase-I) and 110- to 240-g (Phase-II) hybrid striped bass (HSB), as well as their intestinal health. Although glycine serves as an essential substrate for syntheses of creatine and glutathione (GSH) in mammals (e.g., pigs), little is known about these metabolic pathways or their nutritional regulation in fish. This study tested the hypothesis that glycine supplementation enhances the activities of creatine- and GSH-forming enzymes as well as creatine and GSH availabilities in tissues of hybrid striped bass (HSB; Morone saxatilis♀ × Morone chrysops♂).

METHODS

Phase-I and Phase-II HSB were fed a soybean meal-based diet supplemented with 0%, 1%, or 2% glycine for 8 weeks. At the end of the 56-d feeding, tissues (liver, intestine, skeletal muscle, kidneys, and pancreas) were collected for biochemical analyses.

RESULTS

In contrast to terrestrial mammals and birds, creatine synthesis occurred primarily in skeletal muscle from all HSB. The liver was most active in GSH synthesis among the HSB tissues studied. In Phase-I HSB, supplementation with 1% or 2% glycine increased (P < 0.05) concentrations of intramuscular creatine (15%-19%) and hepatic GSH (8%-11%), while reducing (P < 0.05) hepatic GSH sulfide (GSSG)/GSH ratios by 14%-15%, compared with the 0-glycine group; there were no differences (P > 0.05) in these variables between the 1% and 2% glycine groups. In Phase-II HSB, supplementation with 1% and 2% glycine increased (P < 0.05) concentrations of creatine and GSH in the muscle (15%-27%) and liver (11%-20%) in a dose-dependent manner, with reduced ratios of hepatic GSSG/GSH in the 1% or 2% glycine group. In all HSB, supplementation with 1% and 2% glycine dose-dependently increased (P < 0.05) activities of intramuscular arginine:glycine amidinotransferase (22%-41%) and hepatic γ-glutamylcysteine synthetase (17%-37%), with elevated activities of intramuscular guanidinoacetate methyltransferase and hepatic GSH synthetase and GSH reductase in the 1% or 2% glycine group. Glycine supplementation also increased (P < 0.05) concentrations of creatine and activities of its synthetic enzymes in tail kidneys and pancreas, and concentrations of GSH and activities of its synthetic enzymes in the proximal intestine.

CONCLUSIONS

Skeletal muscle and liver are the major organs for creatine and GSH syntheses in HSB, respectively. Dietary glycine intake regulates creatine and GSH syntheses by both Phase-I and Phase-II HSB in a tissue-specific manner. Based on the metabolic data, glycine is a conditionally essential amino acid for the growing fish.

Identification of novel variations in SLC6A8 and GAMT genes causing cerebral creatine deficiency syndrome

Cerebral creatine deficiency syndromes (CCDSs) are a group of rare mendelian disorders mainly characterized by intellectual disability, movement anomaly, behavior disorder and seizures. SLC6A8, GAMT, and GATM are known genes responsible for CCDS. In this study, seven pediatric patients with developmental delay were recruited and submitted to a series of clinical evaluation, laboratory testing, and genetic analysis. The clinical manifestations and core biochemical indications of each child were basically consistent with the diagnosis of CCDS. Genetic diagnosis determined that all patients were positive for SLC6A8 or GAMT variation. A total of 12 variants were identified in this cohort, including six novel ones. The frequency of these variants, the Revel scores and the conservatism of the affected amino acids support their pathogenicity. Our findings expanded the mutation spectrum of CCDS disorders, and provided solid evidence for the counseling to affected families.

Hydrophilic interaction chromatography coupled to tandem mass spectrometry as a method for simultaneous determination of guanidinoacetate and creatine

The biosynthesis of creatine (Cr) is closely related to the bioavailability of guanidinoacetate (GAA). The lack of one or the other may compromise their role in the energy transport and cell signaling. A reliable estimate of their levels in biological samples is imperative since they are important markers of many metabolic disorders. Therefore, a new LC-MS/MS method for simultaneous determination and quantification of GAA and Cr by multiple reaction monitoring (MRM) mode was developed based on the hydrophilic interaction chromatography (HILIC) and response surface methodology (RSM) for the optimization of chromatographic parameters. The optimized parameters ensured good separation of these similar, very polar molecules (chromatographic resolution > 1.5) without prior derivatization step in a short analysis run (6 min). The developed method was validated to ensure accurate (R, 75.1-101.6%), precise (RSD < 20%) and low quantification (LOQ of 0.025 μg mL^-1 for GAA and 0.006 μg mL^-1 for Cr) of the tested analytes and the use of matrix-matched calibration eliminated variable effects of complex matrices such as human plasma and urine. Therefore, this method can be implemented in medical laboratories as a tool for the diagnostics of creatine deficiencies and monitoring of guanidinoacetate and creatine supplementation regimes in biological samples.

Improved Gas Chromatographic Determination of Guanidino Compounds Using Isovaleroylacetone and Ethyl Chloroformate as Derivatizing Reagents

An improved GC method in terms of sensitivity and decrease in the analysis time has been developed for the analysis of eight guanidino compounds: guanidine (G), methylguanidine (MG), creatinine (CTN), guanidinoacetic acid (GAA), guanidinobutyric acid (GBA), guanidinopropionic acid (GPA), argenine (Arg), and guanidinosuccinic acid (GSA), using isovaleroylacetone (IVA) and ethyl chloroformate (ECF) as derivatizing reagents. The separation was obtained from column HP-5 (30 m × 0.32 mm i.d.) with film thickness of 0.25 μm within 11 min. The linear calibrations were obtained with 0.5 to 50 μg/mL with coefficient of determination (R(2)) within 0.9969 - 0.9998. Limits of detections (LODs) were within 5 - 140 ng/mL. The derivatization, separation and determination was repeatable (n = 6) with relative standard deviation (RSD) within 1.2 - 3.1%. The guanidino compounds were determined in deproteinized serum of healthy volunteers and uremic patients within below LOD to 8.8 μg/mL and below LOD to 43.99 μg/mL with RSD within 1.4 - 3.6%. The recovery of guanidino compounds calculated by standard addition from serum was within 96.1 - 98.9%, with RSD 1.4 - 3.6%.

Benzylic rearrangement stable isotope labeling for quantitation of guanidino and ureido compounds in thyroid tissues by liquid chromatography-electrospray ionization mass spectrometry

Benzylic rearrangement stable isotope labeling (BRSIL) was explored to quantify the guanidino and ureido compounds (GCs and UCs). This method employed a common reagent, benzil, to label the guanidino and ureido groups through nucleophilic attacking then benzylic migrating. The use of BRSIL was investigated in the analysis of five GCs (creatine, l-arginine, homoarginine, 4-guanidinobutyric acid, and methylguanidine) and two UCs (urea and citrulline). The labeling was found simple and specific. The introduction of bi-phenyl group and the generation of nitrogen heterocyclic ring in the benzil-d0/d5 labeled GCs and UCs improved the retention behaviors in liquid chromatography (LC) and increased the sensitivity of electrospray ionization mass spectrometry (ESI MS) detection. The fragment ion pairs of m/z 182/187 and m/z 210/215 from the benzil-d0/d5 tags facilitated the discovery of potential GCs and UCs candidates residing in biological matrices. The use of BRSIL combined with LC-ESI MS was applied for simultaneously quantitation of GCs and UCs in thyroid tissues. It was demonstrated that nine GCs and UCs were detected, six of which were further quantified based on corresponding standards. It was concluded that five GCs and UCs (l-arginine, homoarginine, 4-guanidinobutyric acid, methylguanidine, and citrulline) were statistically significantly different (p < 0.05) between the para-carcinoma and carcinoma thyroid tissue samples.

Expanded newborn screening by mass spectrometry: New tests, future perspectives

Tandem mass spectrometry (MS/MS) has become a leading technology used in clinical chemistry and has shown to be particularly sensitive and specific when used in newborn screening (NBS) tests. The success of tandem mass spectrometry is due to important advances in hardware, software and clinical applications during the last 25 years. MS/MS permits a very rapid measurement of many metabolites in different biological specimens by using filter paper spots or directly on biological fluids. Its use in NBS give us the chance to identify possible treatable metabolic disorders even when asymptomatic and the benefits gained by this type of screening is now recognized worldwide. Today the use of MS/MS for second-tier tests and confirmatory testing is promising especially in the early detection of new disorders such as some lysosomal storage disorders, ADA and PNP SCIDs, X-adrenoleucodistrophy (X-ALD), Wilson disease, guanidinoacetate methyltransferase deficiency (GAMT), and Duchenne muscular dystrophy. The new challenge for the future will be reducing the false positive rate by using second-tier tests, avoiding false negative results by using new specific biomarkers and introducing new treatable disorders in NBS programs.

Creatine and guanidinoacetate content of human milk and infant formulas: implications for creatine deficiency syndromes and amino acid metabolism

Creatine is essential for normal neural development; children with inborn errors of creatine synthesis or transport exhibit neurological symptoms such as mental retardation, speech delay and epilepsy. Creatine accretion may occur through dietary intake or de novo creatine synthesis. The objective of the present study was to determine how much creatine an infant must synthesise de novo. We have calculated how much creatine an infant needs to account for urinary creatinine excretion (creatine's breakdown product) and new muscle lay-down. To measure an infant's dietary creatine intake, we measured creatine in mother's milk and in various commercially available infant formulas. Knowing the amount of milk/formula ingested, we calculated the amount of creatine ingested. We have found that a breast-fed infant receives about 9 % of the creatine needed in the diet and that infants fed cows' milk-based formula receive up to 36 % of the creatine needed. However, infants fed a soya-based infant formula receive negligible dietary creatine and must rely solely on de novo creatine synthesis. This is the first time that it has been shown that neonatal creatine accretion is largely due to de novo synthesis and not through dietary intake of creatine. This has important implications both for infants suffering from creatine deficiency syndromes and for neonatal amino acid metabolism.

Guanidinoacetate methyltransferase deficiency: first steps to newborn screening for a treatable neurometabolic disease

BACKGROUND

GAMT deficiency is an autosomal recessive disorder of creatine biosynthesis resulting in severe neurological complications in untreated patients. Currently available treatment is only successful to stop disease progression, but is not sufficient to reverse neurological complications occurring prior to diagnosis. Normal neurodevelopmental outcome in a patient, treated in the newborn period, highlights the importance of early diagnosis.

METHODS

Targeted mutation analysis (c.59G>C and c.327G>A) in the GAMT gene by the QIAxcel system and GAA measurement by a novel two-tier method were performed in 3000 anonymized newborn blood dot spot cards.

RESULTS

None of the targeted mutations were detected in any newborn. Two novel heterozygous variants (c.283_285dupGTC; p.Val95dup and c.278_283delinsCTCGATGCAC; p.Asp93AlafsX35) were identified by coincidence. Carrier frequency for these insertion/deletion types of GAMT mutations was 1/1475 in this small cohort of newborns. GAA levels were at or above the 99th percentile (3.12 μmol/l) in 4 newborns. Second-tier testing showed normal results for 4 newborns revealing 0.1% false positive rate. No GAMT mutations were identified in 4 of the newborns with elevated GAA levels in the first tier testing.

CONCLUSION

This is the first two-tier study to investigate carrier frequency of GAMT deficiency in the small cohort of newborn population to establish evidence base for the first steps toward newborn screening for this treatable neurometabolic disorder.

A simple screening method using ion chromatography for the diagnosis of cerebral creatine deficiency syndromes

Cerebral creatine deficiency syndromes (CCDS) are caused by genetic defects in L-arginine:glycine amidinotransferase, guanidinoacetate methyltransferase or creatine transporter 1. CCDS are characterized by abnormal concentrations of urinary creatine (CR), guanidinoacetic acid (GA), or creatinine (CN). In this study, we describe a simple HPLC method to determine the concentrations of CR, GA, and CN using a weak-acid ion chromatography column with a UV detector without any derivatization. CR, GA, and CN were separated clearly with the retention times (mean ± SD, n = 3) of 5.54 ± 0.0035 min for CR, 6.41 ± 0.0079 min for GA, and 13.53 ± 0.046 min for CN. This new method should provide a simple screening test for the diagnosis of CCDS.

Simultaneous determination of guanidinoacetate, creatine and creatinine in urine and plasma by un-derivatized liquid chromatography-tandem mass spectrometry

Background

Creatine plays an important role in the storage and transmission of phosphate-bound energy. The cerebral creatine deficiency syndromes (CCDS) comprise three inherited defects in creatine biosynthesis and transport. They are characterized by mental retardation, speech and language delay and epilepsy. All three disorders cause low-creatine signal on brain magnetic resonance spectroscopy (MRS); however, MRS may not be readily available and even when it is, biochemical tests are required to determine the underlying disorder.

Methods

Analysis was performed by liquid chromatography-tandem mass spectrometry in positive ionization mode. Samples were analysed underivatized using a rapid ‘dilute and shoot’ approach. Chromatographic separation of the three compounds was achieved. Stable isotope internal standards were used for quantification.

Results

Creatine, creatinine and guanidinoacetate were measured with a 2.5 minute run time. For guanidinoacetate, the standard curve was linear to at least 5000 μmol/L and for creatine and creatinine it was linear to at least 25 mmol/L. The lower limit of quantitation was 0.4 μmol/L for creatine and guanidinoacetate and 0.8 μmol/L for creatinine. Recoveries ranged from 86% to 106% for the three analytes. Intra- and inter-assay variation for each analyte was <10% in both urine and plasma.

Conclusion

A tandem mass spectrometric method has been developed and validated for the underivatized determination of guanidinoacetate, creatine and creatinine in human urine and plasma. Minimal sample preparation coupled with a rapid run time make the method applicable to the routine screening of patients with suspected CCDS.

Creatine synthesis: production of guanidinoacetate by the rat and human kidney in vivo

A fraction of the body's creatine and creatine phosphate spontaneously degrades to creatinine, which is excreted by the kidneys. In humans, this amounts to ∼1–2 g/day and demands a comparable rate of de novo creatine synthesis. This is a two-step process in which l-arginine:glycine amidinotransferase (AGAT) catalyzes the conversion of glycine and arginine to ornithine and guanidinoacetate (GAA); guanidinoacetate methyltransferase (GAMT) then catalyzes the S-adenosylmethionine-dependent methylation of GAA to creatine. AGAT is found in the kidney and GAMT in the liver, which implies an interorgan movement of GAA from the kidney to the liver. We studied the renal production of this metabolite in both rats and humans. In control rats, [GAA] was 5.9 μM in arterial plasma and 10.9 μM in renal venous plasma for a renal arteriovenous (A-V) difference of −5.0 μM. In the rat, infusion of arginine or citrulline markedly increased renal GAA production but infusion of glycine did not. Rats fed 0.4% creatine in their diet had decreased renal AGAT activity and mRNA, an arterial plasma [GAA] of 1.5 μM, and a decreased renal A-V difference for GAA of −0.9 μM. In humans, [GAA] was 2.4 μM in arterial plasma, with a renal A-V difference of −1.1 μM. These studies show, for the first time, that GAA is produced by both rat and human kidneys in vivo.

Anisoin: A useful pre-chromatographic derivatization fluorogenic reagent for LC analysis of guanidino compounds

The use of anisoin as pre-chromatographic reagent for LC analysis of guanidino compounds is proposed. The reagent reacts (5 min at 100 degrees C) with guanidino function and the resulting adducts can be chromatographed under reversed-phase conditions. A fluorescence detector (lambda(ex)=325 nm; lambda(em)=435 nm) was used to detect guanidino adducts. The derivatization and chromatographic conditions were optimised by a series of experiments. Application to the determination of arginine and creatine in pharmaceuticals and arginine, guanidine, methylguanidine, guanidinosuccinic acid, beta-guanidinopropionic acid, gamma-guanidinobutyric acid, guanidinoacetic acid and homoarginine in human urine is described. Quantitation limits ranged from 6 to 30 fmol, except for creatine (510 fmol).

Are cerebral creatine deficiency syndromes on the radar screen?

Cerebral creatine deficiency syndromes (CCDS) are responsible for a considerable proportion of the population affected with mental retardation. CCDS are caused by either an inborn error of the proteins involved in creatine biosynthesis or in the creatine transporter. Besides mental retardation, the clinical characteristics of CCDS are speech and language delay, epilepsy and features of autism. CCDS can be diagnosed by proton magnetic resonance spectroscopy of the brain and/or by biochemical and molecular analysis. Treatment of the defects in creatine biosynthesis has yielded favorable outcomes, while treatments for creatine transporter deficiency are still under investigation at this time. The relatively large contribution of the CCDS to the monogenic causes of mental retardation emphasizes the importance of including CCDS in the differential diagnosis of mental retardation of unknown etiology. Pathophysiology is not yet unravelled, although it is known that creatine plays an important role in energy storage and transmission. Moreover, in vitro data indicate that creatine acts as a neuromodulator in the brain.

Methods for the diagnosis of creatine deficiency syndromes: A comparative study

The increasing number of patients with creatine deficiency syndromes (CDS) stresses the need to develop screening procedures for the identification these inherited disorders. Guanidinoacetate (GAA) and creatine (Cr) are reliable biochemical markers of CDS and several analytical methods to measure both metabolites have been developed. High-pressure liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) is quick and sensitive but, unlike HPLC and gas chromatography-mass spectrometry (GC/MS), it is unavailable in most laboratories. Thus, we decided to evaluate comparatively HPLC-MS/MS, GC/MS and HPLC methods, as well as to establish reference values in a healthy paediatric population. According to our results, these three methods may be suitable for analysing GAA in urine. Furthermore, Passing-Bablock plots showed good agreement among all three. However, when comparing the Cr/Crn ratio, our results revealed that while HPLC-MS/MS data were in agreement with those of GC/MS, a constant and proportional error was observed when compared with those of HPLC. Consequently, the Cr/Crn ratio obtained by the last method should be evaluated with caution. Our reference values for GAA and Cr/Crn ratio in urine negatively correlate with age. Concerning GAA and Cr measurements in plasma, it is interesting to note that in contrast to what was occurring in urine, GAA concentration increased significantly with age, while we did not find any significant difference for Cr values within the same age group.

Assay for the simultaneous determination of guanidinoacetic acid, creatinine and creatine in plasma and urine by capillary electrophoresis UV-detection

Guanidinoacetic acid (GAA) measurement has recently become of great interest for the diagnosis of creatine (Cn) metabolism disorders, and research calls for rapid and inexpensive methods for its detection in plasma and urine in order to assess a large number of patients. We propose a new assay for the measurement of GAA by a simple CZE UV-detection without previous sample derivatization. Plasma samples were filtered by Microcon-10 microconcentrators and directly injected into the capillary, while for urine specimens a simple water dilution before injection was needed. A baseline separation was obtained in less than 8 min using a 60.2 cm x 75 microm uncoated silica capillary, 75 mmol/L Tris-phosphate buffer pH 2.25 at 15 degrees C. The performance of the developed method was assessed by measuring plasma creatinine and Cn in 32 normal subjects and comparing the data obtained by the new method with those found with the previous CE assay. Our new method seems to be an inexpensive, fast and specific tool to assess a large number of patients both in clinical and in research laboratories.

Quantitative determination of guanidinoacetate and creatine in dried blood spot by flow injection analysis-electrospray tandem mass spectrometry

BACKGROUND

Guanidinoacetate (GAA) and creatine (Cr) are reliable biochemical markers of primary creatine disorders. The aim of this study was to develop and validate a method for the determination of GAA and Cr in dried blood spot through the use of stable isotope dilution and flow injection analysis (FIA)-ESI-MS/MS.

METHODS

Dried blood spots were extracted using methanol-water solution containing D3-Cr. After evaporation and formation of butyl esters, samples were analyzed using multiple reaction monitoring mode (m/z 174.2-->101.1 for GAA, 188.3-->90.1 for Cr and 191.3-->93.1 for D3-Cr).

RESULTS

The analysis was very fast (1 min). The detection limits were 0.34 micromol/l of blood and 0.30 micromol/l of blood for Cr and GAA, respectively, and the response was linear over the range 0.25-12.5 micromol/l of blood for GAA and 3.57-624.7 micromol/l of blood for Cr. Recovery range was 93-101% for Cr and 94-105% for GAA and between-run CVs were 5.3% for GAA and 4.5% for Cr. Ion suppression effect was also studied. The method was applied to spots obtained from two patients affected by GAMT deficiency, four patients affected by AGAT deficiency (including a newborn) as well as 282 healthy subjects.

CONCLUSIONS

The detection of GAA in dried blood spot by FIA-ESI-MS/MS is a highly reliable and high throughput method for the diagnosis of GAMT and AGAT deficiencies and a possible tool for newborn screening of both these tractable disorders.

A mutation on exon 6 of guanidinoacetate methyltransferase (GAMT) gene supports a different function for isoform a and b of GAMT enzyme

A new patient affected by Guanidinoacetate methyltransferase (GAMT) deficiency was reported. This 13-year-old girl presented with mental retardation, as main symptom, associated with a typical pattern of biochemical and neurochemical (brain magnetic resonance spectroscopy) alterations. Molecular study detected a L197P transition on exon 6 of the GAMT gene. Since this mutation leaves the isoform B of the GAMT enzyme unaffected, the occurrence of biochemical alterations and disease in this subject testifies against the possibility that isoform b had GAMT activity.

Laboratory diagnosis of defects of creatine biosynthesis and transport

In recent years, three inherited defects in the biosynthesis and transport of creatine have been described. The biosynthetic defects include deficiencies of L-arginine:glycine amidinotransferase and guanidinoacetate methyltransferase. The third defect is a functional defect in the creatine transporter (SLC6A8). Clinical symptoms of the three defects vary in severity, are aspecific and include mental retardation with severe speech delay, autistiform behaviour, and epilepsy. Some patients with GAMT deficiency exhibit a more complex clinical phenotype with extrapyramidal movement disorder. All three defects can be diagnosed by in vivo proton magnetic resonance spectroscopy of the brain, which shows a severe reduction or absence of creatine. Laboratory investigations for the diagnosis start with the analysis of guanidinoacetate, creatine and creatinine in body fluids (plasma and urine). Based on these findings, enzyme assays for AGAT or GAMT, or a creatine uptake assay for the transporter defect can be performed. DNA mutation analysis of the genes involved can prove the defects at the molecular level. To diagnose female patients with SLC6A8 deficiency, mutation analysis may be the only choice.

Improved high-performance liquid chromatographic determination of guanidino compounds by pre-column dervatization with ninhydrin and fluorescence detection

Ninhydrin has been investigated as a pre-column derivatization reagent for guanidino compounds. The reaction takes place under strongly alkaline conditions, followed by a second step at low pH and elevated temperature. This procedure yields derivatives with favourable fluorescence properties (excitation at 390 nm, emission at 470 nm). Amino acids do not react with ninhydrin under these conditions so that the method can easily be used for biological samples. Reversed-phase HPLC separations of the derivatives of several representative guanidino compounds in human blood have been achieved with gradients consisting of aqueous formic acid and methanol. Fluorescence detection yields quantification limits of about 20 microg L(-1). Hyphenation with electrospray mass spectrometry has been used to confirm the identity of the derivatives.

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.

Health implications of creatine: can oral creatine supplementation protect against neurological and atherosclerotic disease?

Major achievements made over the last several years have highlighted the important roles of creatine and the creatine kinase reaction in health and disease. Inborn errors of metabolism have been identified in the three main steps involved in creatine metabolism: arginine:glycine amidinotransferase (AGAT), S-adenosyl-L-methionine:N-guanidinoacetate methyltransferase (GAMT), and the creatine transporter. All these diseases are characterized by a lack of creatine and phosphorylcreatine in the brain, and by (severe) mental retardation. Similarly, knockout mice lacking the brain cytosolic and mitochondrial isoenzymes of creatine kinase displayed a slightly increased creatine concentration, but no phosphorylcreatine in the brain. These mice revealed decreased weight gain and reduced life expectancy, disturbed fat metabolism, behavioral abnormalities and impaired learning capacity. Oral creatine supplementation improved the clinical symptoms in both AGAT and GAMT deficiency, but not in creatine transporter deficiency. In addition, creatine supplementation displayed neuroprotective effects in several animal models of neurological disease, such as Huntington's disease, Parkinson's disease, or amyotrophic lateral sclerosis. All these findings pinpoint to a close correlation between the functional capacity of the creatine kinase/phosphorylcreatine/creatine system and proper brain function. They also offer a starting-point for novel means of delaying neurodegenerative disease, and/or for strengthening memory function and intellectual capabilities.Finally, creatine biosynthesis has been postulated as a major effector of homocysteine concentration in the plasma, which has been identified as an independent graded risk factor for atherosclerotic disease. By decreasing homocysteine production, oral creatine supplementation may, thus, also lower the risk for developing, e.g., coronary heart disease or cerebrovascular disease. Although compelling, these results require further confirmation in clinical studies in humans, together with a thorough evaluation of the safety of oral creatine supplementation.