Background: Tissues with high energy demands, such as the heart, are susceptible to the effects of mitochondrial DNA point mutations. Objective: To investigate the frequency of Wolff-Parkinson-White (WPW) syndrome among a phenotypically and genotypically homogeneous cohort of patients with MELAS (mitochondrial encephalopathy, lactic acidosis, and strokelike episodes) and the A3243G mutation most commonly associated with MELAS syndrome. Design: Survey. Setting: The Pediatric Neuromuscular Disease Center at Columbia University. Patients: Thirty patients with the A3243G mutation and MELAS syndrome enrolled in a clinical trial to assess the effect of dichloroacetate on neurologic symptoms. Interventions: Medical histories and electrocardiograms were reviewed and DNA samples from fibroblasts, urine and cheek epithelial cells, leukocytes, and hair were analyzed to determine mitochondrial mutation abundance and estimate total mutation burden. Results: Four of 30 patients (13%) had a clinical history of, or electrocardiographic findings consistent with, WPW syndrome. In 2 patients, WPW syndrome preceded MELAS syndrome by 15 and 21 years. The tissue burden of mutant mitochondria was similar in patients with (49.4%) and without (39.1%) WPW syndrome. Conclusions: The prevalence of WPW syndrome among patients with MELAS syndrome and the A3243G mutation appears much higher than in the normal population and may become manifest earlier than neurologic symptoms. Patients with WPW syndrome and neurologic abnormalities consistent with MELAS syndrome, such as seizures, deafness, short stature, and stroke, should be screened for the A3243G mutation. Moreover, patients with MELAS syndrome should be monitored for cardiac anomalies including cardiomyopathy and WPW syndrome.
