Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessive inborn error of creatine biosynthesis caused by a deficiency of hepatic guanidinoacetate methyltransferase, resulting in a lack of creatine and an accumulation of guanidinoacetic acid, the precursor of creatine. GAMT deficiency is characterized by developmental arrest or delay in the first few months of life with epilepsy and extrapyramidal movements as common features. Neurologic signs and symptoms are variable, and autistic spectrum disorders are sometimes seen in older affected individuals. Pathophysiology of GAMT deficiency is thought that the accumulation of guanidinoacetate can interact with neuronal GABAA receptors and cause the neurological dysfunction which underlies these symptoms.
