GATM and cerebral creatine deficiency syndrome: This innovative system for creatine delivery might be a game changer for the cure of creatine deficiency syndromes, a family of three inherited metabolic disorders caused by mutations in the genes encoding for the synthetic enzymes of creatine (L-arginine:glycine amidinotransferase, AGAT, and S-adenosyl-L-methionine:N-guanidinoacetate methyltransferase, GAMT) or the transporter responsible for its cellular uptake (CRT).