Molecular Analysis of tRNAGlu, Trp, Ala, Asp Genes of mtDNA in Patients with Long QT Syndrome

Background and Long QT syndrome is a heart arrhythmia identified by prolongation of the QT interval which is a cause of sudden cardiac death in young individuals. In most cases, abnormalities in heart repolarization are reasons of prolongation of action potential and arrhythmia. The activity of ion channels is sensitive to ATP level, therefore, mitochondrial disorders are considered to be very important. The purpose of this study was to investigate the areas of mtDNA that are identified as hot spots in most cardiac diseases. Total DNA was extracted from the peripheral blood of 30 patients with LQT syndrome and 35 normal persons. Mitochondrial tRNATrp-Ala-Apn-Glugenes and cytochrome b gene were amplified by polymerase chain reaction (PCR). Then, PCR fragments were screened for singlestrand conformation polymorphism analysis (SSCP) and all positive samples were sequenced. We observed a homoplasmic and conserved T14687C mutation in the mitochondrial tRNA glutamic acid gene in one patient with pervious syncope. We found a homoplasmic C14766T transition in five patients that changed threonine to isoleucine substitution at amino acid 7. Also, we found a heteroplasmy G14838A mutation in mitochondrial cytochrome b gene which is nonsense and changed tryptophan to a stop codon in position 31. Mitochondria ATP synthesis is important in heart, therefore, it is possible that mutations in mitochondrial genes could constitute a predisposing factor in combination with environmental factors and may also trigger the syncope in patients with L QT.