Smoking switches on a killer gene which can cause women to become infertile, researchers in the US have found.

Smoking has long been associated with infertility and early menopause. Scientists report that they have identified the path which leads from women smoking to the premature death of their egg cells. Tobacco smoke contains a class of chemicals called polycyclic aromatic hydrocarbons (PAH). A team led by Jonathan Tilly, of the Massachusetts general hospital in Boston, discovered that PAH triggers the activity in egg cells of a gene called Bax, known to play a pivotal role in killing cells. The researchers, who publish their work today in the journal Nature Genetics, ex posed female mice to PAH. Their eggs were destroyed. Mr Tilly's team then grafted human ovarian tissue, containing eggs, under the skin of mice. "When the mice were given a single injection of the PAH compound there was a striking increase in degenerating eggs in the human ovarian tissues," wrote the group. "This supports the notion that the earlier menopause seen in female smokers might be due to the death of their eggs."

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