Alteration in mitochondrial DNA plays an important role in the development and progression of cancer. The Displacement Loop (D-loop) region of mitochondrial DNA (mtDNA) is the regulatory region for its replication and transcription. Therefore, we aimed to characterize mutations in the D-loop region of mitochondrial DNA along with the morphological changes and analyzed their impact on survival in retinoblastoma patients. mtDNA D-loop region was amplified by Nested-Polymerase Chain Reaction (Nested-PCR) and mutations were analyzed in 60 tumor samples from retinoblastoma patients by DNA sequencing. Transmission electron microscopy was performed on 5 retinoblastoma specimens. Mutations were correlated with clinical, histopathological parameters and patient survival. D-loop mutations were found in total of 52/60 (86.6%) patients. The most common mutations were T to C and C to T followed by A to G. There were 5.81% mutations which were not previously reported in the MITOMAP database. A73G (83.33%) were the most frequent mutations found in our cases and it was statistically significant with poor tumor differentiation and age. In addition, this study was further analyzed for morphological changes in retinoblastoma that had disorganized, swollen and less numbers of mitochondria on electron microscopy. This is the first study showing high frequency of mtDNA mutation which might be due to abnormal morphology of mitochondria in retinoblastoma. Our results indicate that pathogenic mtDNA D-loop mutations may be involved in tumorigenesis of retinoblastoma tumor.
Retinoblastoma D-loop Mitochondrial DNA DNA sequencing Electron microscopy
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LS was responsible for designing and executing the experiment. NS helps in sequencing analysis. SK and SS did the histopathological evaluation. TCN did the electron microscopy evaluation. SB was responsible for providing follow up. NP was responsible proving samples.
This study was funded by Indian Council of Medical Research, New Delhi, INDIA (Award no: 5/4/6/09/Oph/2012-NCD II).
Compliance with Ethical Standards
Conflict of Interest
No potential conflicts of interest with any author.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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