Identification of a Large-scale Mitochondrial DNA Deletion in Iranian Heart Arrhythmia Patients(LQT Syndrome)

Long QT Syndrome is one of the arrhythmic disorders of the heart that causes sudden cardiac death in patients. Most of the investigations have focused on nuclear genome for finding genetic defects in these disorders, but some of the cases with LQTS cannot be explained by mutations of identified genes. It prompted the authors to focus on the mitochondrial DNA and monitor rearrangements which are probably the cause of respiratory chain defects and reduced ATP generation. The region of the mitochondrial DNA(from 5461 to 15000 nt) was screened by PCR amplification and southern blot followed by DNA sequence analysis. For the first time, a large scale deletion(~8.7 kb) was identified in 30 of the39 patients (76.3%) using Multiplex PCR and Southern blot analysis and demonstrated that this deletion is flanked by 9bp direct repeat. The results also showed that this deletion in patient samples was higher than normal controls(P<0.001). Of the total,8 aged subjects(> 45 years old) had multiple deletions in the region between 5461 and 16150 that may be an age effect on the occurrence of rearrangements on mitochondrial genome. Since heart is highly dependent on oxidative energy generated in mitochondria, such a large scale deletion may be the link between these diseases and dysfunctions of mitochondria.