Guanidinoacetate Methyltransferase Deficiency (Creatine-Deficiency-Syndrome) is a rare autosomal recessive disease caused by a mutation in the GAMT gene which codes for guanidinoacetate N-methyltransferase. A deficiency in this enzyme results in accumulation of 3-methylglutaconic acid in urine; guanidoacetic acid in urine and serum. Decreased concentrations of creatine are found in serum and urine; and creatinine in plasma, spinal fluid, and urine. Symptoms, which present at birth, include failure to thrive, mental and motor retardation, hyoptonia, and seizures. Treatment includes arginine-restricted diet, sodium benzoate, and L-ornithine hydrochlorate.