Reversible brain creatine deficiency in two sisters with normal blood creatine level

We describe a new creatine metabolism disorder in 2 young sisters who suffe red from mental retardation and severe language delay. Blood examination, i nvestigation of the most common neurometabolic disorders, and brain magneti c resonance imaging were normal. Diagnosis was established only by means of in vivo proton magnetic resonance spectroscopy, which disclosed generalize d depletion of creatine in the brain. Creatine monohydrate oral administrat ion led to almost complete brain creatine level restoration along with impr ovement of the patients' disabilities.