Heritability of Breast Cancer

Heritability of Breast Cancer

A study performed by Rowell et al. showed that the instances of monozygotic twins both having breast cancer is higher than the instances of dizygotic twins both having breast cancer.  This information is valuable to our discussion of heritability because twins show levels of concordance.  Monozygotic (identical) twins share 100% of their genes, while dizygotic twins share only about 50% of their genes.  This research indicates that 10% of all breast cancers are heritable because of the prevalence of familial cases. 

Familial cases of breast cancer are most often observed after menopause. Because of the late onset of breast cancer, it usually does not effect the reproductive period of females.  Therefore does not have an affect on the fitness of the affected individual.  Because most individuals have already reproduced offspring before signs of breast cancer appear, selection against traits that may cause breast cancer are not existent.  Many researchers have come to the conclusion that breast cancer is likely passed through autosomal inheritance. 

Another factor that may be a partial cause of breast cancer is dense breast tissue.  Dense breast tissue, when visible on a mammogram, is linked with higher risk of breast cancer.  A study was performed on twins in Australia, Canada, and the United States to find if dense breast tissue is a heritable trait.  The findings showed 65% of the variation in density was due to heritability. 

The gene that codes for breast cancer is believed to be on chromosome 11 in human genome.  Research has shown that deletion of traits of chromosome 11 have a strong correlation with tumors and breast cancer.  The deletion on the short arm of chromosome 11 suggests that recessive mutations may be the underlying cause of breast cancer.  Because cancer is thought to be caused by recessive traits, inbreeding will most likely cause breast cancer to be far more common among the population.

 

References:

Boyd NF, Dite GS, Stone J, Gunasekara A, English DR, McCredie MR, Giles GG, Tritchler D, Chiarelli A, Yaffe MJ,Hopper JL. Heritability of mammographic density, a risk factor for breast cancer.  N Engl J Med. 2002 Sep 19;347(12):886-94.  Division of Epidemiology and Statistics, Ontario Cancer Institute, Toronto, Canada.

Lippman, Marc E., Dickson, Robert Brent. Breast Cancer: Cellular and Molecular Biology.  Springer 1988

Mack, T M;  Hamilton, A S;  Press, M F;  Diep, A; and Rappaport, E B.  Heritable breast cancer in twins   British Journal of Cancer (2002) 87, 294–300. doi:10.1038/sj.bjc.6600429 www.bjcancer.com. Published online 23 July 2002

Rowell S, Newman B, Boyd J, King M-C (1994) Inherited predisposition to breast and ovarian cancer. Am J Hum Genet 55: 861–865