It's not exactly news that smoking cigarettes is bad for you, but this latest danger is a doozy: smoking damages your genome. The largest genetic study of smoking ever has identified over 300 genes that are negatively affected by cigarettes.

The study looked at white blood cells from over a thousand people in the hopes of isolating specific genes whose expression was altered by smoking cigarettes. It's just one of many studies being undertaken as part of the San Antonio Family Heart Study, which has spent years examining health issues in the Texas city's Mexican American community, but this particular test is probably the most ambitious.

Research leader Jac Charlesworth explains what they found and why it's significant:

"Previous studies of gene expression as influenced by smoking have been seriously limited in size with the largest of the in vivo studies including only 42 smokers and 43 non-smokers. We studied 1,240 individuals, including 297 current smokers. Never before has such a clear link between smoking and transcriptomics [effects on gene expression] been revealed, and the scale at which exposure to cigarette smoke appears to influence the expression levels of our genes is sobering."

The genetic effects observed fit into a variety of categories that correlate well with the known physical effects of smoking, such as decreased immune response, cell death, increased risk of cancer, metabolism of foreign particles, and natural killer cell signaling. Taken as a whole, the study points out just how deep the damage of smoking goes.

As Charlesworth puts it: "Our results indicate that not only individual genes but entire networks of gene interaction are influenced by cigarette smoking. It is likely that this observed effect of smoking on transcription has larger implications for human disease risk, especially in relation to the increased risk of a wide variety of cancers throughout the body as a result of cigarette smoke exposure"

(IO9, 16/07/2010)