Cigarette smoking can alter DNA in sperm and cause genetic damage which could pass to offspring, according to a new study.

Smoking can cause changes in the DNA sequence of sperm cells, alterations that could potentially be inherited by offspring, Canadian researchers found in the study published by the journal of the American Association for Cancer Research.

The researchers at Health Canada and McMaster University studied the spermatogonial stem cells of mature mice that had been exposed to cigarette smoke for either six or 12 weeks to look for alterations in a specific stretch of repeated portions of DNA, called Ms6-hm, which does not contain any known genes.

The mice were exposed to two cigarettes per day, the equivalent based on blood levels of tobacco by-products of an average human smoker.

The findings show that the rate of Ms6-hm mutations in the smoking mice were 1.4 times higher than that of non-smoking mice at six weeks, and 1.7 times that of non-smoking mice at 12 weeks.

This suggests that damage is related to the duration of exposure, so the longer people smoke the more mutations accumulate and the more likely a potential effect may arise in the offspring, said the study.

"Here we are looking at male germline mutations, which are mutations in the DNA of sperm. If inherited, these mutations persist as irreversible changes in the genetic composition of off- spring," said Carole Yauk, Ph.D., lead author of the study and research scientist at Health Canada's Environmental and Occupational Toxicology Division.

"We have known that mothers who smoke can harm their fetuses, and here we show evidence that fathers can potentially damage offspring long before they may even meet their future mate," she said.

Males, whether they are mouse or man, generate a constant supply of new sperm from self-renewing spermatogonial stem cells.

Yauk said previous studies have shown that Ms6-hm and similar locations of non-coding DNA are sensitive to damage from radiation, mutagenic chemicals and intense industrial air particulate pollution.

While the researchers did not specifically study the protein- coding regions of DNA where genes reside, Yauk notes that previous studies correlate mutations in non-coding regions with those in coding regions, and that some repetitive regions of DNA (not examined in this study) are associated with genes.

"It stands to reason that mutations could also interfere with genes, but our ongoing research looks to clarify the severity of DNA damage throughout the genome," said Yauk.

Source: Xinhua