As previously reported, the identification of creatine deficiency syndromes (CDS) caused by mutations in the L-arginine:glycine amidinotransferase (AGAT) [2], guanidinoacetate methyltransferase deficiency (GAMT) [3], and SLC6A8 genes [4] highlights the essential role of intact creatine metabolism in psychomotor development and cognitive function in humans. The gene discussed is GATM; the disease is cerebral creatine deficiency syndrome.