Levels of purine and pyridine nucleotides and their metabolites were determined in erythrocytes and plasma of 31 Rett pattients and 17 age-matched controls at the Departments of Molecular Biology and Child Psychiatry, University of Siena, Children’s Hospital, Siena, Italy. No difference was found in erythrocyte nucleotide concentrations, but plasma nicotinamide levels were significantly lower in Rett syndrome patients compared to controls. Erythrocyte activities of hypoxanthine phosphoribosyl transferase, adenine pbt and pbpp synthetase were also lower. The production rate of pyridine nucleotides from nicotinic acid by erythrocytes was increased in Rett patients. The significance of these metabolic changes was not determined. 
COMMENT. Despite frequent reports of various and diverse metabolic changes in patients with Rett syndrome, no consistent and diagnostic biochemical test has been identified for this disorder. The diagnosis is based on agreed clinical criteria. Alterations in nucleotide metabolism are an interesting addition to the search for a specific cause.