A rare but treatable inborn error of metabolism: Arginine:glycine amidinotransferase (AGAT) deficiency

AGAT deficiency is a rare and treatable autosomal recessive disorder. The symptoms are early-onset developmental mild to moderate intellectual disability, delayed speech acquisition, behavioral problems or proximal muscle weakness. Biochemical screening for creatine, creatinine and urinary guanidinoacetate and genetic tests are used for diagnosis. Electromyography may be normal or may have a myopathic pattern with low amplitude polyphasic waves. Muscle biopsy may show abnormalities including small myocytes. Creatine supplementation can fully prevent the neurological disability, if the treatment is started early in life; the muscular function improves irrespective of the supplementation moment.