Guanidinoacetate methyltransferase deficiency is a newly discovered disorder of creatine biosynthesis. Its manifestation starts in infant age by extrapyramidal symptoms, epilepsy, progressive loss of motor and mental functions, psychomotor retardation, muscular weakness as well as other neurological symptoms in context with a low serum and urinary level of creatinine. This new hereditary metabolic disorder is curable. Creatine substitution led to clinical improvement in all patients detected so far. The authors emphasize that only by early diagnosis and treatment it is possible to prevent irreversible brain damage in these children.

        Key words: guanidinoacetate methyltransferase deficiency, creatine, extrapyramidal symptoms, epi- lepsy, treatment, magnetic resonance spectroscopy