Smoking causes mutation in sperm DNA: Health Canada Study Links Smoking to Potential Heritable Effects
20 Jul, 2007 01:44 pm
Smoking is known to cause cancer and other diseases, but new evidence suggests that smoking may also permanently alter the DNA sequence of the descendents of fathers who smoke.
The researchers exposed mature male mice by inhalation to 2 cigarettes per day alongside unexposed mice for 6 or 12 weeks. Based on blood levels of tobacco by-products found in mice exposed using the same system, the exposure is comparable to that of an average human smoker. The investigators quantified the number of DNA sequence changes arising in the sperm stem cells of the exposed and control males. The results, published in the June 1 issue of the journal Cancer Research, showed that mice exposed to cigarette smoke for 6 or 12 weeks had 1.4 and 1.7 times higher sperm mutation frequencies. The findings suggest that the longer the mouse was exposed to smoke, the more mutations accumulated in the sperm stem cells.
This research is the first to show that exposure to mainstream tobacco smoke causes DNA sequence mutation in sperm. Therefore, the study suggests that the descendants of male smokers may inherit permanent changes in DNA that arose in the sperm of their fathers. The researchers looked for alterations in a specific stretch of repeated portions of DNA, called Ms6-hm, which does not contain any known genes. Because the region of DNA examined in the study does not have a known function, it is unclear at this time how this result relates to health outcome in the descendants. However, the regions of DNA examined in mice are also found in humans and follow-up investigations will examine the potential human health outcomes of this finding.
The next steps the researchers plan to take will examine how altered DNA manifests itself in the children and grandchildren of male mice that are exposed to firsthand and secondhand smoke. Further work will determine whether there is a recommended period for cessation of smoking prior to reproducing.
Yauk’s colleagues include fellow researchers from Health Canada and Martin Stämpfli, Ph.D., and his laboratory team at McMaster University. Funding for this research was provided by grants from the Canadian Regulatory System for Biotechnology and the Canadian Institutes of Health Research.
Carole L. Yauk, et al, Mainstream Tobacco Smoke Causes Paternal Germ-Line DNA Mutation, Cancer Research 67, 5103-5106, June 1, 2007