Patients affected by cerebral creatine deficiency syndrome-1 (CCDS1) share depletion of brain Cr and the clinical phenotype with patients carrying the other two defects of Cr metabolism which involve mutations of genes encoding the biosynthesizing enzymes AGAT and GAMT (Itemet al., 2001;Stockleret al., 1994). This evidence concerns the gene GATM and creatine transporter deficiency.