Guanidinoacetate Methyltransferase Deficiency Research Articles

Electro-clinical features and long-term outcomes in guanidinoacetate methyltransferase (GAMT) deficiency

ObjectiveTo evaluate clinical characteristics and long-term outcomes in patients with guanidinoacetate methyltransferase (GAMT) deficiency with a special emphasis on seizures and electroencephalography (EEG) findings. MethodsWe retrospectively analyzed the clinical and molecular characteristics, seizure types, EEG findings, neuroimaging features, clinical severity scores, and treatment outcomes in six patients diagnosed with GAMT deficiency. ResultsMedian age at presentation and diagnosis were 11.5 months (8–12 months) and 63 months (18 months −11 years), respectively. Median duration of follow-up was 14 years. Global developmental delay (6/6) and seizures (5/6) were the most common symptoms. Four patients presented with febrile seizures. The age at seizure-onset ranged between 8 months and 4 years. Most common seizure types were generalized tonic seizures (n = 4) and motor seizures resulting in drop attacks (n = 3). Slow background activity (n = 5) and generalized irregular sharp and slow waves (n = 3) were the most common EEG findings. Burst-suppression and electrical status epilepticus during slow-wave sleep (ESES) pattern was present in one patient. Three of six patients had drug-resistant epilepsy. Post-treatment clinical severity scores showed improvement regarding movement disorders and epilepsy. All patients were seizure-free in the follow-up. ConclusionsEpilepsy is one of the main symptoms in GAMT deficiency with various seizure types and non-specific EEG findings. Early diagnosis and initiation of treatment are crucial for better seizure and cognitive outcomes. This long-term follow up study highlights to include cerebral creatine deficiency syndromes in the differential diagnosis of patients with global developmental delay and epilepsy and describes the course under treatment.

Evidence of an intracellular creatine-sensing mechanism that modulates creatine biosynthesis via AGAT expression in human HAP1 cells

Cellular homeostasis of creatine (CT), integral part of the energy buffering and transducing system connecting intracellular sites of ATP production and utilization, comprises of mechanisms that increase CT, i.e., biosynthesis and cellular uptake, and CT-lowering processes, such as export and non-enzymatic conversion to creatinine. The biosynthesis of CT is controlled by negative feedback loop via suppression of the rate-limiting enzyme arginine:glycine amidinotransferase (AGAT). Although the regulatory mechanism involved is not well understood, AGAT suppression is successfully used in patients with guanidinoacetate methyltransferase (GAMT) deficiency to reduce the neurotoxic accumulation of the AGAT-mediated guanidinoacetate production by supplementing patients with CT. Utilizing the CT-dependent feedback loop for the upregulation of AGAT expression may well represent a therapeutic target for an additional CT deficiency syndrome, the CT transporter (CrT) defect, for which no effective treatment option is available so far. We have used CRISPR to tag the C-terminus of AGAT with a nanoluc luciferase (NLuc) reporter in HAP1 cells. A biphasic decay of AGAT-NLuc in response to increasing extracellular CT was observed, whereas the decrease in AGAT-NLuc expression was directly proportional to the rise in intracellular CT levels with an approximate IC50 of 1–2 mM. CRISPR generated HAP1 CrT null cells and HAP1 CrT null cells stably expressing a CrT-GFP fusion protein further demonstrated that the biphasic response to extracellular CT is mediated by a high-affinity (Km 9–10 µM) CrT dependent, saturable mechanism and a CrT independent, unsaturable uptake process. The direct response to intracellular CT suggests the existence of an intracellular CT sensing system enabling a dynamic cell response to changing CT concentration that is relevant for cellular CT homeostasis.

Evidence and Recommendation for Guanidinoacetate Methyltransferase Deficiency Newborn Screening.

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessive disorder of creatine biosynthesis due to pathogenic variants in the GAMT gene that lead to cerebral creatine deficiency and neurotoxic levels of guanidinoacetate. Untreated, GAMT deficiency is associated with hypotonia, significant intellectual disability, limited speech development, recurrent seizures, behavior problems, and involuntary movements. The birth prevalence of GAMT deficiency is likely between 0.5 and 2 per million live births. On the basis of small case series and sibling data, presymptomatic treatment with oral supplements of creatine, ornithine, and sodium benzoate, and a protein-restricted diet to reduce arginine intake, appear to substantially improve health and developmental outcomes. Without newborn screening, diagnosis typically happens after the development of significant impairment, when treatment has limited utility. GAMT deficiency newborn screening can be incorporated into the tandem-mass spectrometry screening that is already routinely used for newborn screening, with about 1 per 100 000 newborns screening positive. After a positive screen, diagnosis is established by finding an elevated guanidinoacetate concentration and low creatine concentration in the blood. Although GAMT deficiency is significantly more rare than other conditions included in newborn screening, the feasibility of screening, the low number of positive results, the relative ease of diagnosis, and the expected benefit of presymptomatic dietary therapy led to a recommendation from the Advisory Committee on Heritable Disorders in Newborns and Children to the Secretary of Health and Human Services that GAMT deficiency be added to the Recommended Uniform Screening Panel. This recommendation was accepted in January 2023.

Fourteen cases of cerebral creatine deficiency syndrome in children: a cohort study in China.

This study sought to analyze the clinical characteristics, biochemical metabolic indications, treatment results, and genetic spectrum of cerebral creatine deficiency syndrome (CCDS), estimate the prevalence of CCDS in Chinese children and provide a reference to guide clinical practice. We performed a retrospective cohort study of 3,568 children with developmental delay at Children's Hospital of Fudan University over a 6-year period (January 2017-December 2022). Metabolites in the blood/urine were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and genetic testing was performed by next-generation sequencing (NGS). The patients with suspected CCDS were ultimately diagnosed by magnetic resonance spectroscopy (MRS). The patients were then treated and followed up. All the reported cases of CCDS, their gene mutations, and treatment results in China were summarized. Ultimately, 14 patients were diagnosed with CCDS. The age of onset was between 1-2 years. All the patients had developmental delay, 9 had epilepsy, and 8 had movement or behavioral disorders. A total of 17 genetic variants were identified, including 6 novel variants. c.403G>A, c.491dupG of the guanidinoacetate methyltransferase (GAMT) gene had a relatively high frequency. After treatment, patients with GAMT deficiency showed obvious improvements, and brain creatine (Cr) levels recovered to 50-80% of normal, 1 patient achieved normal neurodevelopment, and 3 patients became epilepsy free; however, 6 male patients with X-linked creatine transporter gene (SLC6A8) variants received Cr for 3-6 months with no effect, and 2 patients received combined therapy with few improvements. The prevalence of CCDS is ~0.39% in Chinese children with developmental delay. Alow-protein diet, Cr and, ornithine were useful for patients with GAMT deficiency. Male patients with SLC6A8 deficiency showed only limited improvement on combined therapy.

Novel guanidinoacetate methyltransferase (GAMT) mutation associated with cerebral creatine deficiency syndrome in a Syrian child: a case report.

A 2.5-year-old boy presented to the paediatric neurology clinic with evidence of neurodevelopmental delays and intellectual disabilities. Recurrent eye blinking, generalized non-motor (absence) seizures, hyperactivity, and poor eye contact were revealed in the neurological examination. Some athetoid and dystonic movements were noticed. His electroencephalography (EEG) was very disturbed because of generalized spike-wave and slow-wave discharges. Based on these findings antiepileptic drugs were administered. His seizures slightly improved, but then relapsed with myoclonic and drop attacks. After 6 years of unbeneficial treatment, a genetic test was required. Whole-exome sequencing was conducted and identified a novel homozygous GAMT variant (NM_138924.2:c.391+5G>C). Treatment with oral creatine supplementation, ornithine, and sodium benzoate was administered. After 1.7 years of follow-up, the child was almost seizure-free with a remarkable reduction of epileptic activity on EEG. He demonstrated good-but not complete-behavioural and motor improvement due to delayed diagnosis and treatment. GAMT deficiency should be considered in differential diagnoses in children with neurodevelopmental regression along with drug-refractory epilepsy. A special concern is needed in Syria for such genetic disorders; regarding the high prevalence of consanguinity. Whole-exome sequencing and genetic analysis can be used to diagnose this disorder. We reported a novel GAMT variant to extend its mutation spectrum and provide an additional molecular marker for the definitive diagnosis of GAMT deficiency patients and prenatal diagnosis in the affected families.

Creatine Deficiency Disorders: Phenotypes, Genotypes, Diagnosis, and Treatment Outcomes

Creatine is synthetized from arginine and glycine. There are two enzymes in the synthesis: l-arginine:glycine amidinotransferase and guanidinoacetate methyltransferase. After the synthesis, it is taken up by high-energy-requiring organs using creatine transporter. Biallelic pathogenic variants in GAMT result in guanidinoacetate methyltransferase deficiency and biallelic pathogenic variants in GATM result in l-arginine:glycine amidinotransferase deficiency. Hemizygous pathogenic variant in males and heterozygous pathogenic variant in females in SLC6A8 result in creatine transporter deficiency. Patients with these disorders present with a wide range of symptoms, including developmental delay, seizures, movement disorder, behavioral problems, and hypotonia. The diagnosis can be suspected by elevated guanidinoacetate and low creatine levels in body fluids in guanidinoacetate methyltransferase deficiency, low guanidinoacetate and low creatine levels in body fluids in l-arginine:glycine amidinotransferase deficiency, and elevated creatine-to-creatinine ratio in urine in creatine transporter deficiency in males as well as absent or significantly decreased creatine level in brain proton magnetic resonance spectroscopy. Genetic investigations such as targeted next-generation sequencing panel or exome sequencing can also identify these disorders; however, metabolite measurements and creatine in proton magnetic resonance spectroscopy are crucial to confirm the diagnosis. While all 3 disorders are currently treated with creatine supplementation, guanidinoacetate methyltransferase deficiency is also treated with ornithine supplementation and a protein- or arginine-restricted diet, and creatine transporter deficiency is treated with arginine and glycine supplementation (with no proven improvements).

Development of a Universal Second-Tier Newborn Screening LC-MS/MS Method for Amino Acids, Lysophosphatidylcholines, and Organic Acids.

First-tier MS-based newborn screening by flow injection analysis can have high presumptive positive rates, often due to isomeric/isobaric compounds or poor biomarker specificity. These presumptive positive samples can be analyzed by second-tier screening assays employing separations such as liquid chromatography-mass spectrometry (LC-MS/MS), which increases test specificity and drastically reduces false positive referrals. The ability to screen for multiple disorders in a single multiplexed test simplifies workflows and maximizes public health laboratories' resources. In this study, we developed and validated a highly multiplexed second-tier method for dried blood spots using a hydrophilic interaction liquid chromatography (HILIC) column coupled to an MS/MS system. The LC-MS/MS method was capable of simultaneously detecting second-tier biomarkers for maple syrup urine disease, homocystinuria, methylmalonic acidemia, propionic acidemia, glutaric acidemia type 1, glutaric acidemia type 2, guanidinoacetate methyltransferase deficiency, short-chain acyl-CoA dehydrogenase deficiency, adrenoleukodystrophy, and Pompe disease.

Guanidinoacetate Methyltransferase Deficiency, a Treatable Neurodevelopmental Disorder

AbstractGuanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessive inborn error of creatine synthesis that results in intellectual disability, epilepsy, expressive language delay, and dystonia. We report data from two siblings with an uncommon GAMT deficiency phenotype and their clinical, biochemical, imaging, and treatment findings. The older sibling had intellectual disability, epilepsy, and generalized dystonia. The younger sibling had intellectual disability and generalized dystonia. After treatment with creatine, verbal fluency improved, as well as dystonia and aggression. This study confirms that in patients with unexplained intellectual disability, epilepsy, and/or movement disorders, GAMT deficiency should be considered. GAMT-associated cerebral creatine deficiency syndrome is a potentially treatable condition and can be identified by elevated levels of guanidinoacetate in plasma or urine or by a significantly decreased creatine peak on magnetic resonance spectroscopy.

Expanding the neuroimaging findings of guanidinoacetate methyltransferase deficiency in an Iranian girl with a homozygous frameshift variant in the GAMT.

Guanidinoacetate methyltransferase deficiency (GAMTD) is a treatable neurodevelopmental disorder with normal or nonspecific imaging findings. Here, we reported a 14-month-old girl with GAMTD and novel findings on brain magnetic resonance imaging (MRI).A 14-‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍month-old female patient was referred to Myelin Disorders Clinic due to onset of seizures and developmental regression following routine vaccination at 4months of age. Brain MRI, prior to initiation of treatment, showed high signal intensity in T2-weighted imaging in bilateral thalami, globus pallidus, subthalamic nuclei, substantia nigra, dentate nuclei, central tegmental tracts in the brainstem, and posterior periventricular white matter which was masquerading for mitochondrial leukodystrophy. Basic metabolic tests were normal except for low urine creatinine; however, exome sequencing identified a homozygous frameshift deletion variant [NM_000156: c.491del; (p.Gly164AlafsTer14)] in the GAMT. Biallelic pathogenic or likely pathogenic variants cause GAMTD. We confirmed the homozygous state for this variant in the proband, as well as the heterozygote state in the parents by Sanger sequencing.MRI features in GAMTD can mimic mitochondrial leukodystrophy. Pediatric neurologists should be aware of variable MRI findings in GAMTD since they would be misleading to other diagnoses.

GAMT Deficiency Among Pediatric Population: Clinical and Molecular Characteristics and Management.

Objective: Analyze the treatment modalities used in real practice by synthesizing available literature. Methods: We reviewed and evaluated 52 cases of GAMT deficiency including 4 novel cases from Saudi Arabia diagnosed using whole-exome sequencing. All data utilized graphical presentation in the form of line charts and illustrated graphs. Results: The mean current age of was 117 months (±29.03) (range 12-372 months). The mean age of disease onset was 28.32 months (±13.68) (range 8 days - 252 months). The most prevalent symptom was developmental delays, mainly speech and motor, seizures, and intellectual disability. The male-to-female ratio was 3:1. Multiple treatments were used, with 54 pharmacological interventions, valproic acid being the most common. Creatinine monohydrate was the prevalent dietary intervention, with 25 patients reporting an improvement. Conclusion: The study suggests that efficient treatment with appropriate dietary intervention can improve patients' health, stressing that personalized treatment programs are essential in managing this disorder.

Lack of Epileptogenic Effects of the Creatine Precursor Guanidinoacetic Acid on Neuronal Cultures In Vitro.

The creatine precursor Guanidinoacetic Acid (GAA) accumulates in the genetic deficiency of the GuanidinoAcetate Methyl Transferase (GAMT) enzyme and it is believed to cause the seizures that often occur in this condition. However, evidence that it is indeed epileptogenic is scarce and we previously found that it does not cause neuronal hyperexcitation in in vitro brain slices. Here, we used Micro-Electrode Arrays (MEAs) to further investigate the electrophysiological effects of its acute and chronic administration in the networks of cultured neurons, either neocortical or hippocampal. We found that: (1) GAA at the 1 µM concentration, comparable to its concentration in normal cerebrospinal fluid, does not modify any of the parameters we investigated in either neuronal type; (2) at the 10 µM concentration, very similar to that found in the GAMT deficiency, it did not affect any of the parameters we tested except the bursting rate of neocortical networks and the burst duration of hippocampal networks, both of which were decreased, a change pointing in a direction opposite to epileptogenesis; (3) at the very high and unphysiological 100 µM concentration, it caused a decrease in all parameters, a change that again goes in the direction opposite to epileptogenesis. Our results confirm that GAA is not epileptogenic.

Morphological Studies of the Left Ventricle in the Creatine Deficiency Mice Model

IntroductionHeart failure is the major cause of death characterized by changes in myocardial energetics, including a reduced level of creatine. In organs with high energy demand such as the heart, creatine is taken up by cardiomyocytes via creatine transporter with subsequent transformation into phosphocreatine, which controls by creatine kinase. This system functions as shuttles high‐energy phosphates from mitochondria to contractile elements such as the myofibril, which utilize 70 % of total produced energy by mitochondria. For the past decades, many studies tried to understand whether a reduced level of creatine affects the myocardial function leading to the failing heart. However, most of the results from these studies have been contradictory. The present study describes the detailed morphologic changes of cardiomyocytes of the left ventricle (LV) of mice with whole‐body creatine deficiency due to knockout of the biosynthetic enzyme (guanidinoacetate N‐methyltransferase, GAMT).Methods & ResultsThe present study used GAMT‐/‐ mice model with the unique metabolic fingerprint of zero creatine similar to those in human GAMT deficiency. The histological and transmission electron microscopy (TEM) studies of LV myocardium in GAMT‐/‐ mice showed cardiac hypertrophy and increased collagen accumulation in the myocardial interstitium compared to the wild‐type (WT) mice. The TEM examination showed irreversible destructive ultrastructure changes of cardiomyocytes in conjunction with insufficient adaptive protein synthesis accompanied by focal and diffuse lysis of myofilaments in cardiac myocytes. The mitochondrial changes were characterized by cristae homogenization and fragmentation in association with cluster formation. The volume of density of mitochondria (VvMt), myofibrils (VvMf), and their ratios (VvMt/VvMf), along with the coefficient of energy efficiency of mitochondria (CEEM) have been examined in GAMT‐/‐ mice in comparison to WT. We established that VvMt, VvMf, VvMt/VvMf, and CEEM were all significantly reduced. Further, destructive changes in the nucleus and nuclei, focal degradation of sarcoplasm, increases autophagy, are all evidence of inadequate adaptive protein synthesis in cardiac myocytes.ConclusionsThese studies of GAMT‐/‐ mice demonstrated that creatine deficiency promotes decreased VvMt/VvMf and CEEM in LV myocytes, which may contribute to the development progression of heart failure and in conjunction with insufficient adaptive protein synthesis contribute to irreversible ultrastructure restructuring of cardiomyocytes with loss contractile myocardial function.

Gene therapy for guanidinoacetate methyltransferase deficiency restores cerebral and myocardial creatine while resolving behavioral abnormalities

Creatine deficiency disorders are inborn errors of creatine metabolism, an energy homeostasis molecule. One of these, guanidinoacetate N-methyltransferase (GAMT) deficiency, has clinical characteristics that include features of autism, self-mutilation, intellectual disability, and seizures, with approximately 40% having a disorder of movement; failure to thrive can also be a component. Along with low creatine levels, guanidinoacetic acid (GAA) toxicity has been implicated in the pathophysiology of the disorder. Present-day therapy with oral creatine to control GAA lacks efficacy; seizures can persist. Dietary management and pharmacological ornithine treatment are challenging. Using an AAV-based gene therapy approach to express human codon-optimized GAMT in hepatocytes, in situ hybridization, and immunostaining, we demonstrated pan-hepatic GAMT expression. Serial collection of blood demonstrated a marked early and sustained reduction of GAA with normalization of plasma creatine; urinary GAA levels also markedly declined. The terminal time point demonstrated marked improvement in cerebral and myocardial creatine levels. In conjunction with the biochemical findings, treated mice gained weight to nearly match their wild-type littermates, while behavioral studies demonstrated resolution of abnormalities; PET-CT imaging demonstrated improvement in brain metabolism. In conclusion, a gene therapy approach can result in long-term normalization of GAA with increased creatine in guanidinoacetate N-methyltransferase deficiency and at the same time resolves the behavioral phenotype in a murine model of the disorder. These findings have important implications for the development of a new therapy for this abnormality of creatine metabolism.

Method modification to reduce false positives for newborn screening of guanidinoacetate methyltransferase deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessive disorder that results in reduced activity of guanidinoacetate methyltransferase, an accumulation of guanidinoacetate (GUAC), and a lack of cerebral creatine (CRE). Lack of CRE in the brain can cause intellectual disability, autistic-like behavior, seizures, and movement disorders. Identification at birth and immediate therapy can prevent intellectual disability and seizures. If started early in life, treatment with creatine supplements is highly effective. Because there are reliable biomarkers for GAMT deficiency, GUAC and CRE, and because the disorder is readily treatable with a significant improvement in outcomes, GAMT deficiency is an excellent candidate for newborn screening. Several programs have conducted pilot programs or started screening. An isobaric interferant of the GUAC marker has been reported which may cause false positive results. To reduce the number of false positives, a second-tier HPLC test to separate GUAC from unknown, isobaric interferants may be incorporated into the screening algorithm. New York State began screening for GAMT deficiency in October 2018 using a three-tiered screening approach. Quantification of GUAC and CRE were incorporated into routine screening for amino acids and acylcarnitines. In the first year of screening a total of 263,739 samples were tested for GAMT deficiency. Of these, 3382 required second tier testing. After second tier testing, 210 repeat specimens were requested for borderline results and 10 referrals were made to specialty care centers for confirmatory testing. In the first year of screening there were no confirmed cases of GAMT deficiency detected. To reduce the number of samples needing second tier testing and the number false positives we explored the use of a second MS transition to confirm the identity of the GUAC marker. GUAC and its internal standard are detected as butylated esters after sample preparation and derivatization. The original method used transition of the GUAC molecular ion of m/z 174.1 to a reactant ion of m/z 101.1. To confirm the identity of the GUAC marker we selected a qualifier ion of 174.1 > 73. The alternative product ion results were found to agree more closely with the second tier HPLC-MS/MS results for GUAC. It was found that the alternative transition may be used for quantification of the GUAC marker with acceptable analytical performance (linearity, accuracy, and precision). On March 5, 2020, the method of analysis for GUAC was modified to use the alternative product ion. For a comparable 6-month period, the modified method reduced the number of samples requiring second tier testing by 98%, reduced the number of borderline results requiring a repeat sample by 87.5%, and reduced the number of referrals to specialty care centers by 85%. Using the modified method, the correlation (r-squared) of the first and second tier screening results for GUAC is greater than 0.95. Since the first-tier results correlate well with the second-tier results, the second-tier screening is no longer necessary with the modified method.

Engineering new metabolic pathways in isolated cells for the degradation of guanidinoacetic acid and simultaneous production of creatine

Here we report, for the first time, the engineering of human red blood cells (RBCs) with an entire metabolic pathway as a potential strategy to treat patients with guanidinoacetate methyltransferase (GAMT) deficiency, capable of reducing the high toxic levels of guanidinoacetate acid (GAA) and restoring proper creatine levels in blood and tissues. We first produced a recombinant form of native human GAMT without any tags to encapsulate into RBCs. Due to the poor solubility and stability features of the recombinant enzyme, both bioinformatics studies and extensive optimization work were performed to select a mutant GAMT enzyme, where only four critical residues were replaced, as a lead candidate. However, GAMT-loaded RBCs were ineffective in GAA consumption and creatine production because of the limiting intra-erythrocytic S-adenosyl methionine (SAM) content unable to support GAMT activity. Therefore, a recombinant form of human methionine adenosyl transferase (MAT) was developed. RBCs co-entrapped with both GAMT and MAT enzymes performed, in vitro, as a competent cellular bioreactor to remove GAA and produce creatine, fueled by physiological concentrations of methionine and the ATP generated by glycolysis. Our results highlight that metabolic engineering of RBCs is possible and represents proof of concept for the design of novel therapeutic approaches.

Effects of Delivering Guanidinoacetic Acid or Its Prodrug to the Neural Tissue: Possible Relevance for Creatine Transporter Deficiency.

The creatine precursor guanidinoacetate (GAA) was used as a dietary supplement in humans with no adverse events. Nevertheless, it has been suggested that GAA is epileptogenic or toxic to the nervous system. However, increased GAA content in rodents affected by guanidinoacetate methyltransferase (GAMT) deficiency might be responsible for their spared muscle function. Given these conflicting data, and lacking experimental evidence, we investigated whether GAA affected synaptic transmission in brain hippocampal slices. Incubation with 11.5 μM GAA (the highest concentration in the cerebrospinal fluid of GAMT-deficient patients) did not change the postsynaptic compound action potential. Even 1 or 2 mM had no effect, while 4 mM caused a reversible decrease in the potential. Guanidinoacetate increased creatine and phosphocreatine, but not after blocking the creatine transporter (also used by GAA). In an attempt to allow the brain delivery of GAA when there was a creatine transporter deficiency, we synthesized diacetyl guanidinoacetic acid ethyl ester (diacetyl-GAAE), a lipophilic derivative. In brain slices, 0.1 mM did not cause electrophysiological changes and improved tissue viability after blockage of the creatine transporter. However, diacetyl-GAAE did not increase creatine nor phosphocreatine in brain slices after blockage of the creatine transporter. We conclude that: (1) upon acute administration, GAA is neither epileptogenic nor neurotoxic; (2) Diacetyl-GAAE improves tissue viability after blockage of the creatine transporter but not through an increase in creatine or phosphocreatine. Diacetyl-GAAE might give rise to a GAA–phosphoGAA system that vicariates the missing creatine–phosphocreatine system. Our in vitro data show that GAA supplementation may be safe in the short term, and that a lipophilic GAA prodrug may be useful in creatine transporter deficiency.

Guanidinoacetate Methyltransferase Deficiency: A Treatable Cause of Developmental Delay Diagnosed by Magnetic Resonance Spectroscopy.

Guanidinoacetate Methyltransferase Deficiency: A Treatable Cause of Developmental Delay Diagnosed by Magnetic Resonance Spectroscopy.

Laboratory Diagnosis of Cerebral Creatine Deficiency Syndromes by Determining Creatine and Guanidinoacetate in Plasma and Urine.

Cerebral creatine deficiency syndromes are caused by the dysfunctional creatine biosynthesis or transport and comprise three hereditary neurodevelopmental defects including arginine-glycine amidinotransferase (AGAT), guanidinoacetate methyltransferase (GAMT), and creatine transporter deficiencies. All conditions are characterized by seizures, intellectual disability, and behavioral abnormalities. Laboratory diagnosis of these disorders relies on the determination of creatine and guanidinoacetate concentrations in both plasma and urine. Here we describe a rapid quantitative UPLC/MS/MS method for the simultaneous determination of these analytes using a normal-phase HILIC column after analyte derivatization. The approach is suitable for neonatal screening follow-ups and monitoring of the treatment for creatine deficiency syndromes.

Cerebral creatine deficiency disorders – A clinical, genetic and follow up study from India

IntroductionCerebral creatine deficiency syndromes (CCDS) are a group of potentially treatable neurometabolic disorders. The clinical, genetic profile and follow up outcome of Indian CCDS patients is presented. Materials and methodsThis was a retrospective cohort of CCDS patients seen over six-years. Diagnosis was based either on low creatine peak on proton magnetic resonance spectroscopy (MRS) and/or genetic evaluation. ResultsThirteen patients were eligible [8 creatine transporter deficiency (CTD), 4 guanidinoacetate methyltransferase (GAMT) deficiency and 1 could not be classified]. The mean (±SD) age at diagnosis was 7.2(±5.0) years.Clinical manifestations included intellectual disability (ID) with significant expressive speech delay in all. Most had significant behavior issues (8/13) and/or autism (8/13). All had history of convulsive seizures (11/13 had epilepsy; 2 patients only had febrile seizures) and 2/13 had movement disorder. Constipation was the commonest non-neurological manifestation (5/13 patients).Cranial MRI was normal in all CTD patients but showed globus pallidus hyperintensity in all four with GAMT deficiency. MRS performed in 11/13 patients, revealed abnormally low creatine peak. A causative genetic variant (novel mutation in nine) was identified in 12 patients.Three GAMT deficiency and one CTD patient reported neurodevelopmental improvement and good seizure control after creatine supplementation. ConclusionIntellectual disability, disproportionate speech delay, autism, and epilepsy, were common in our CCDS patients. A normal structural neuroimaging with easily controlled febrile and/or afebrile seizures differentiated CTD from GAMT deficiency patients who had abnormal neuroimaging and often difficult to control epilepsy and movement disorder.

Creatine metabolism in patients with urea cycle disorders

The urea cycle generates arginine that is one of the major precursors for creatine biosynthesis. Here we evaluate levels of creatine and guanidinoacetate (the precursor in the synthesis of creatine) in plasma samples (ns = 207) of patients (np = 73) with different types of urea cycle disorders (ornithine transcarbamylase deficiency (ns = 22; np = 7), citrullinemia type 1 (ns = 60; np = 22), argininosuccinic aciduria (ns = 81; np = 31), arginase deficiency (ns = 44; np = 13)). The concentration of plasma guanidinoacetate positively correlated (p < 0.001, R2 = 0.64) with levels of arginine, but not with glycine in all patients with urea cycle defects, rising to levels above normal in most samples (34 out of 44) of patients with arginase deficiency. In contrast to patients with guanidinoacetate methyltransferase deficiency (a disorder of creatine synthesis characterized by elevated guanidinoacetate concentrations), creatine levels were normal (32 out of 44) or above normal (12 out of 44) in samples from patients with arginase deficiency. Creatine levels correlated significantly, but poorly (p < 0.01, R2 = 0.1) with guanidinoacetate levels and, despite being overall in the normal range in patients with all other urea cycle disorders, were occasionally below normal in some patients with argininosuccinic acid synthase and lyase deficiency. Creatine levels positively correlated with levels of methionine (p < 0.001, R2 = 0.16), the donor of the methyl group for creatine synthesis. The direct correlation of arginine levels with guanidinoacetate in patients with urea cycle disorders explains the increased concentration of guanidino compounds in arginase deficiency. Low creatine levels in some patients with other urea cycle defects might be explained by low protein intake (creatine is naturally present in meat) and relative or absolute intracellular arginine deficiency.