Rett syndrome is a severe neurological developmental disorder. In this syndrome, the high incidence of sudden death is correlated with an alteration of ventricular repolarization. The purpose of this study was to evaluate plasmatic levels of nerve growth factor (NGF) in Rett patients with prolonged corrected QT (QTc) interval in comparison with those of Rett patients with normal QTc. We observed 23 female Rett patients (9.9+/-4.7 years). NGF plasma levels and QTc interval were measured in all patients. Student t-test was performed for statistical analysis. NGF plasma levels were significantly lower in Rett patients with QTc interval prolongation (QTc > 0.44 sec) in comparison with Rett patients with a normal QTc interval (4.5+/-4.5 vs 11+/-8.3 pg/ml, p = 0.02). The alteration of NGF levels, observed in Rett patients with a long QTc interval, may explain the presence of an altered ventricular repolarization associated with a higher risk of cardiac arrhythmias.