GAMT Deficiency: Clinical Presentation, Treatment, Diagnosis, Animal Models, Preclinical and Clinical Developments.

Guanidinoacetate Methyl Transferase (GAMT) deficiency is a rare disease characterized by neurodevelopmental derangements, epilepsy, and movement disorders. The condition arises from the combined effect of postnatal brain creatine (Cr) depletion and guanidinoacetate (GAA) toxicity. Consequently, current treatment relies on Cr supplementation and metabolic management to reduce GAA accumulation by limiting its synthesis through ornithine supplementation and precursor reduction. Although effective in preventing the severe GAMT phenotype, the therapy is limited in normalizing these metabolites' concentrations. Recently, interest has been growing in approaches aimed at restoring the mutant enzyme as the primary step toward a cure. Some of these approaches have been investigated at the preclinical level and are here summarized. Interestingly, a mouse model that replicates most of the patients' features is now available in various labs, and the strong commitment of the Association for Creatine Deficiency has fostered the coordination and support of many of these models' initiatives. This review introduces readers to the complexity of this ultrarare condition, describes current therapeutic approaches, provides information about the most accurate methods for an early diagnosis, and outlines the main features of the available animal models. Finally, some current preclinical investigations are described, along with some preliminary expectations of emerging data.