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Creatine in the human body is derived from two sources: the diet and endogenous synthesis. Biosynthesis involves two enzymes: l-arginine:glycine amidinotransferase (EC 2.1.4.1) and guanidinoacetate N -methyltransferase (GAMT; EC 2.1.1.2). Defects in both of these enzymes lead to inborn errors of metabolism (1)(2). Deficiency of l-arginine:glycine amidinotransferase has been reported very recently in two patients by Item et al. (3) and Bianchi et al. (4). GAMT deficiency was first described in 1994 (1)(5). The clinical presentation of the disease varies widely (2)(6). Some patients present with intractable epilepsy, extrapyramidal movement disorder, and severe retardation, whereas other patients have much milder symptoms and show only mild retardation and autistic behavior. The aspecific clinical picture of GAMT deficiency and the relatively good treatment options makes a good diagnostic strategy important. Magnetic resonance spectroscopy of the brains of affected patients shows absence of the creatine/creatine phosphate peak. However, magnetic resonance spectroscopy may not be performed on all patients with mild symptoms. Screening for metabolic disorders may also aid in the diagnosis because generalized increases in amino acids, organic acids, and other metabolites can be found when their concentrations are calculated relative to the creatinine concentration (2). The relatively low creatinine excretion in GAMT patients, which is attributable to the creatine deficiency, gives falsely increased values for a range of metabolites when they are calculated relative to creatinine. When GAMT deficiency is suspected, analysis of guanidinoacetate in plasma should be performed (7)(8). Confirmation of the defect can be obtained by enzymatic and DNA analysis (9)(10). Ilas et al. (11) described an assay for the determination of GAMT in fibroblasts and lymphoblasts. This method uses 14C-labeled guanidinoacetate as substrate. Product formation ([14C]creatine) is determined by HPLC with detection …

Guanidinoacetate methyltransferase (GAMT; EC 2.1.1.2) deficiency (OMIM 601240) is an autosomal recessive disorder of creatine biosynthesis, characterized clinically by mental retardation, language delay, extrapyramidal movements, epilepsy, and autistic behavior (1). Biochemically, GAMT deficiency is characterized by depletion of creatine and accumulation of guanidinoacetate (GAA) in the brain and body fluids (2). Treatment by creatine supplementation (combined with arginine restriction and ornithine supplementation) partially restores (∼70%) cerebral creatine, reduces seizures, and improves behavior, but it does not reverse the mental retardation (3). We have described a method to measure GAA and creatine in plasma and urine by liquid chromatography–tandem mass spectrometry (LC-MS/MS) (4). In the present study, we validated this method for measurement of GAA and creatine in amniotic fluid, and we report the first GAMT prenatal diagnosis based on a combination of molecular and biochemical investigations. We …

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 …