SLC6A8 and psychiatric disorder: Individuals with genetic Cr disorders characterized by mental dysfunction, including arginine–glycine amidinotransferase (AGAT), guanidinoacetate methyltransferase (GAMT), or solute carrier family 6 member 8 (SLC6A8) deficiencies, have also been shown to benefit from early Cr supplementation (Schulze and Battini 2007).