VNTR Polymorphism in the Intron 5 of SIRT3 and Susceptibility to Breast Cancer.

Background: Breast cancer recurrence and metastasis are associated with alterations in the cellular stress responses that influence tumour signalling. Sirtuin3 (SIRT3), a mitochondrial deacetylase is the regulator of mitochondrial metabolism and oxidative stress affecting tumour cell responses. Genetic variants or dysregulation of SIRT3 was known to associate with poor prognosis of recurrence and relapse in few cancers.

Methods: The current case-control study was conducted in Hyderabad, India. A total of 200 primary female breast cancer cases were recruited, irrespective of age and clinical subtype. However, secondary or recurrent breast cancer cases were excluded from the study. A total of 202 age and gender-matched healthy controls without any familial inheritance of either breast or other cancer and having similar ethnicity as cases were recruited. The blood samples of both cases and controls were collected from Nizam's Institute of Medical Sciences (NIMS), Hyderabad. Our study is an attempt to evaluate the association of SIRT3 VNTR polymorphism in intron 5 with the development and progression of breast cancer by PCR-based genotyping.  Result: The statistical analysis of the results with respect to epidemiological and clinical phenotypes revealed significant association of 0R allele and 0R/0R genotype with breast cancer risk (p<0.01). The odds ratios also were found to be significant i.e., 0R/0R [OR(CI): 2.67(1.54-4.65); p=0.000005] genotype. Also, the epidemiological and clinical variables have shown significant association with the risk of onset of the disease. Therefore, the influence of lack of repeats at intron 5 harbouring enhancer site on altered expression of SIRT3 might confer increased susceptibility to breast cancer.

Conclusion: The VNTR polymorphism in the intron 5 region of SIRT3 gene could serve as a molecular marker for detection of breast cancer onset. Further studies are warranted to study the prognostic and therapeutic significance of this SIRT3 polymorphism.