A creatine deficiency syndrome characterized by global developmental delay/intellectual disability (DD/ID), prominent speech delay, autistic/hyperactive behavioral disorders, seizures, and various types of pyramidal and/or extra-pyramidal manifestations. The disease is Monarch Disease Ontology id MONDO_0012999 (guanidinoacetate methyltransferase deficiency). Also known as: GAMT deficiency, cerebral creatine deficiency syndrome 2, cerebral creatine deficiency syndrome type 2, disorder of guanidinoacetate N-methyltransferase activity, guanidinoacetate N-methyltransferase activity disease.