High frequency of common deletion (4981 bp) in mitochondrial DNA in nasopharyngeal carcinoma and its correlation with patient age and clinical stages

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Mitochondrial DNA (mtDNA) has a high mutation rate due at least in part to a lack of protective histones and an inefficient DNA repair system. The most frequently change in mtDNA is the so-called Common Deletion (CD), which accumulates in patients with hetero-plasmic mtDNA mutations and in normal individuals during aging. In this study, wild type mtDNA (WT-mtDNA) and mitochondrial DNA with CD (CD-mtDNA) were quantitatively analyzed in different nasopharynx lesions. A novel type of CD-mtDNA (4981 bp) was de-tected significantly higher in nasopharyngeal carcinoma (NPC) (93%, 54/58) than in naso-pharyngitis (60%, 28/47) and the paired white blood cells (WBC) (26%, 8/31). The ratio of CD-mtDNA to WT-mtDNA in NPC (0.000625, median) was 10 times that in nasopharyngitis (0.000064, median) (P = 0.003), and was significantly higher than that in paired WBC (0.000000, median) (P = 0.000). The CD/WT-mtDNA ratio was 0.000564 (quartile range, 0.000184 - 0.000919) in late stage NPC, which was nearly 3 times the ratio in early stage NPC (0.000164, quartile range, 0.000042 - 0.000353) (P = 0.015, Mann-Whitney Test). In NPC patients with ages °› 48yrs (mean age), the ratio of CD-mtDNA to WT-mtDNA was 0.000625, which was nearly 10 times that in NPC patients with ages < 48yrs (0.000064) (P = 0.005, Mann-Whitney Test). This is the first quantitative study of CD-mtDNA mutations in NPC, which provides evidences that CD-mtDNA mutation might be involved in the devel-opment and progression of NPC.