The authors studied methionine and creatine metabolism in females with Rett syndrome. Plasma metabolites (including methionine, homocysteine, guanidinoacetate) and urine creatine/creatinine ratios in 29 females with Rett syndrome were within the age-appropriate range. Although the authors have not been able to identify any abnormalities, it can be speculated that patients with Rett syndrome may benefit from dietary intervention to increase the supply of labile methyl groups to affected tissues.