L-Arginine:glycine amidinotransferase (AGAT) deficiency is a very rare type of creatine deficiency sydrome characterized by global developmental delay, intellectual disability, and myopathy. The disease is AGAT deficiency (MONDO_0012996). Also known as: CCDS3, GATM deficiency, L-arginine:glycine amidinotransferase deficiency, arginine:glycine amidinotransferase deficiency, cerebral creatine deficiency syndrome 3, cerebral creatine deficiency syndrome type 3, creatine deficiency syndrome due to AGAT deficiency, disorder of glycine amidinotransferase activity.