Intellectual Disability and Brain Creatine Deficit: Phenotyping of the Genetic Mouse Model for GAMT Deficiency.

Prospective identification by neonatal screening of patients with guanidinoacetate methyltransferase deficiency

Currently there are 91 treatable inborn errors of metabolism that cause intellectual developmental disorders. Cerebral creatine deficiencies (CDD) comprise three of these: arginine: glycine amidinotransferase [AGAT], guanidinoacetate methyltransferase [GAMT], and X-linked creatine transporter deficiency [SLC6A8]. Intellectual developmental disorder and cerebral creatine deficiency are the hallmarks of CDD. Additional clinical features include prominent speech delay, autism, epilepsy, extrapyramidal movement disorders, and signal changes in the globus pallidus. Patients with GAMT deficiency exhibit the most severe clinical spectrum. Myopathy is a distinct feature in AGAT deficiency. Guanidinoacetate (GAA) is the immediate product in the creatine biosynthetic pathway. Low GAA concentrations in urine, plasma, and cerebrospinal fluid are characteristic diagnostic markers for AGAT deficiency, while high GAA concentrations are characteristic markers for GAMT deficiency. An elevated ratio of urinary creatine /creatinine excretion serves as a diagnostic marker in males with SLC6A8 deficiency. Treatment strategies include oral supplementation of high-dose creatine-monohydrate for all three CDD. Guanidinoacetate-reducing strategies (high-dose ornithine, arginine-restricted diet) are additionally employed in GAMT deficiency. Supplementation of substrates for intracerebral creatine synthesis (arginine, glycine) has been used additionally to treat SLC6A8 deficiency. Early recognition and treatment improves outcomes. Normal outcomes in neonatally ascertained siblings from index families with AGAT and GAMT deficiency suggest a potential benefit of newborn screening for these disorders.

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. 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. In the three AGAT patients, plasma GAA was 0.01-0.04 micro mol/L [mean (SD) for neurologically normal controls was 1.16 (0.59) micromol/L], Cr+Crn was 15-29 micro mol/L [reference limit in our laboratory, 79 (38) micromol/L]. Urinary GAA was 2.4-5.8 micro mol/L [reference, 311 (191) micromol/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 micromol/L, respectively), and Cr+Crn was decreased in plasma (10.7 micromol/L) and urine (2.1 mmol/L). GAA was increased in the parents' plasmas and in the mother's urine. The assessment of GAA is a new tool for the detection of both GAMT and AGAT deficiencies.

Creatine deficiency syndromes are a newly described group of inborn errors of creatine synthesis (arginine:glycine amidinotransferase (AGAT) deficiency and guanidinoacetate methyltransferase (GAMT) deficiency) and of creatine transport (creatine transporter (CRTR) deficiency). The common clinical feature of creatine deficiency syndromes is mental retardation and epilepsy suggesting main involvement of cerebral gray matter. The typical biochemical abnormality of creatine deficiency syndromes is cerebral creatine deficiency, which is demonstrated by in vivo proton magnetic resonance spectroscopy. Measurement of guanidinoacetate in body fluids may discriminate between the GAMT (high concentration), AGAT (low concentration) and CRTR (normal concentration) deficiencies. Further biochemical characteristics include changes in creatine and creatinine concentrations in body fluids. GAMT and AGAT deficiency are treatable by oral creatine supplementation, while patients with CRTR deficiency do not respond to this type of treatment. The creatine deficiency syndromes are underdiagnosed, so their possibility should be considered in all children affected by unexplained mental retardation, seizures and speech delay.

Adolescent girl with unexplained intellectual disability in who was identified a defect in the biosynthesis of creatine by guanidinoacetate methyltransferase (GAMT) deficiency. Were identified two GAMT gene mutations: c.59G>C in exon 1 and c.521G>A in exon 5. The creatine and ornitine substitution and arginine restriction, despite initiated at 13 years old, motivated a global behaviour comportmental acceleration. The GAMT deficiency is an inborn error of metabolism with molecular and clinical heterogeneity varying from a speech delay to autistic behaviour and severe cognitive deficit. Should be considered in patients with unexplained intellec tual disability, especially in Portugal where was documented a high frequency of patients and carriers. The pertinence of the neonatal screen in our country is discussed.

Guanidinoacetate N-methyltransferase deficiency: Case report and brief review of the literature

Treatment outcome of twenty-two patients with guanidinoacetate methyltransferase deficiency: An international retrospective cohort study.

Guanidinoacetate 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.

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessively inherited disorder of the metabolism of creatine that leads to depleted levels of creatine and excessive concentrati...

Evaluation of the mechanism underlying the inhibitory effect of guanidinoacetate on brain Na+, K+-ATPase activity

Creatine is an organic compound used as fast phosphate energy buffer to recycle ATP, important in tissues with high energy demand such as muscle or brain. Creatine is taken from the diet or endogenously synthetized by the enzymes AGAT and GAMT, and specifically taken up by the transporter SLC6A8. Deficit in the endogenous synthesis or in the transport leads to Cerebral Creatine Deficiency Syndromes (CCDS). CCDS are characterized by brain creatine deficiency, intellectual disability with severe speech delay, behavioral troubles such as attention deficits and/or autistic features, and epilepsy. Among CCDS, the X-linked creatine transporter deficiency (CTD) is the most prevalent with no efficient treatment so far. Different mouse models of CTD were generated by doing long deletions in the Slc6a8 gene showing reduced brain creatine and cognitive deficiencies or impaired motor function. We present a new knock-in (KI) rat model of CTD holding an identical point mutation found in patients with reported lack of transporter activity. KI males showed brain creatine deficiency, increased urinary creatine/creatinine ratio, cognitive deficits and autistic-like traits. The Slc6a8Y389C KI rat fairly enriches the spectrum of CTD models and provides new data about the pathology, being the first animal model of CTD carrying a point mutation.

3 - Creatine deficiency syndromes

Cerebral creatine deficiency disorders that result in very low levels of creatine in the brain, can cause in intellectual disability, seizures, expressive speech disorder and behavior disorders if not treated in early childhood. CCDDs comprise disorders of creatine synthesis (arginine:glycine [AGAT; MIM 602360]; guanidinoacetate methyltransferase deficiency [GAMT; MIM 601240]) and of creatine transport (SLC6A8 deficiency [SLC6A8; MIM 300036]). Inborn errors of creatine synthesis-but not, as yet, of transport-can be treated by creatine substitution and are thus treatable causes of intellectual disability.

Guanidino compounds in guanidinoacetate methyltransferase deficiency, a new inborn error of creatine synthesis

Guanidinoacetate methyltransferase [(GAMT); EC 2.1.1.2] deficiency is the first recognized inborn error of creatine biosynthesis, manifesting in infancy with severe neurologic symptoms such as epilepsy, mental retardation, muscular hypotonia, and progressive extrapyramidal movement disorder (1). Patients with GAMT deficiency have shown favorable responses to oral supplementation of creatine-monohydrate, but complete reversal of symptoms has not been observed (2). Biochemical findings include high urinary excretion of guanidinoacetate (the immediate precursor of creatine and substrate of GAMT), low urinary excretion of creatinine [conversion product of intracellular creatine; see Ref. (3)], and depletion of creatine in brain and muscle (4). After assessing two index patients (5)(6), we aimed to establish methods for the noninvasive molecular diagnosis of GAMT deficiency. We recently developed a radiochemical method for the determination of GAMT activity in cultured skin fibroblasts and in virus-transformed lymphoblasts (7). Here we report a denaturing gradient gel electrophoresis (DGGE) technique for the screening of mutations in the GAMT gene in DNA extracted from dried-blood spot filter-paper samples and from fibroblasts and virus-transformed lymphoblasts. Three index patients with mutations confirmed by techniques other than DGGE [P1, P2, and P6; see Refs. (5), (8)] and three new patients (P3, P4, and P5) with undetectable GAMT activity but unknown GAMT deficiency mutations (9)(10) were investigated. Details of the patient studies are summarized in Table 1⇓ , and the locations and frequencies of the mutations identified in these patients are shown in Fig. 1⇓ . We extracted DNA from dried-blood spot, filter-paper samples and from fibroblasts and lymphoblasts using …