EVALUATION OF MITOCHONDRIAL DNA MUTATIONS IN SIX FAMILIES BY RESEQUENCING ARRAY

Objective: Human mitochondrial DNA is a circular, double stranded molecule which is inherited through maternal lineage. Point mutations in tRNA, rRNA or protein coding genes and structural rearrangements such as partial deletions or duplications can cause mitochondrial disorders. The prevalence of mitochondrial diseases is estimated to be 1/5000 worldwide. For the analysis of mtDNA mutations, Sanger sequencing, Southern blot, long and quantitative PCR, Resequencing Array and next-generation sequencing methods can be used. In this study, we analysed whole mitochondrial genomes of six children (along with their mothers) who were admitted to Gazi University Hospital with symptoms suggestive of mitochondrial disease. Materials and Methods: After the extraction of genomic DNA from six children and their mothers, mtDNA resequencing with the analysis of obtained data was performed. In order to determine whether one of the mutations found in Patient 4 was homoplasmic or heteroplasmic, PCR and RFLP techniques were also used. Results: Among six patients included in this study group, none of the variants detected could be attributed to any mitochondrial diseases, except the pathogenic mutation detected in Patient 4. The m.3460 G>A mutation detected in Patient 4 was located in the MT-ND1 gene that was known to be responsible for LHON. This mutation detected in Patient 4 was also detected both in his mother and sister with homoplasmic state. The lack of clinical findings in his mother and sister was thought to be due to decreased penetrance of the disease in females and modifying genes in nuclear genome. Conclusion: Screening of mtDNA using resequencing method could provide fast, effective and more reliable results in the diagnosis of mitochondrial diseases. Also, currently, the NGS technology analysis of nuclear DNA along with mtDNA will provide more reliable results in diagnosis of mitochondrial diseases, thus allowing more accurate genotype-phenotype correlation.