Frequent somatic mutations of mitochondrial DNA in traditional serrated adenomas but not in sessile serrated adenomas of the colorectum

Background and Aim: Serrated adenomas (SAs), recently subdivided into traditional SAs (TSAs) and sessile SAs (SSAs), are recognized as a distinct form of neoplasia of the colorectum. One of the characteristics of SAs is hypermaturation of the gland epithelium due to the low extent of cell loss by apoptosis. Mutations of mitochondrial DNA (mtDNA) are closely associated with abnormality in apoptosis. We therefore examined mtDNA mutations in colorectal lesions including hyperplastic polyps (HPs), SSAs, TSAs, and carcinomas. Methods: Examined were 25 HPs, 32 SSAs, 19 TSAs, and 138 carcinomas. The D310 region of the mtDNAs was examined by microsatellite assay. Results: mtDNA mutations were detected in none of 25 (0%) HPs, one of 32 (3%) SSAs, six of 19 (32%) TSAs, and eleven of 133 (8%) carcinomas (five of the 138 carcinomas were not informative). The frequency of mtDNA mutations in the TSAs was significantly higher than that in the HPs, SSAs, and carcinomas (P = 0.004, P = 0.008, and P = 0.009, respectively). The frequency of mtDNA mutations in carcinomas was not significantly higher than that in HPs and SSAs (P = 0.14 and P = 0.28, respectively). Conclusion: Our data suggest that mtDNA mutations may play an important role in the development of TSAs and could be used as a genetic marker to aid in the diagnosis of colorectal lesions.