New Delhi, Oct. 30: A defective version of an enzyme that helps expel toxins from the body raises the risk of prostate cancer among tobacco users, according to scientists studying the genetics of this male cancer in Indians.

Doctors at the Sanjay Gandhi Postgraduate Institute of Medical Sciences in Lucknow have shown that genetic variations that lead to a faulty version of the enzyme called NAT2 determine the risk of prostate cancer in tobacco users.

“Men who have this defective enzyme and who use tobacco appear to have a higher risk of prostate cancer than men who don’t have this defective enzyme and who don’t use tobacco,” said Dr Rama Mittal of the urology department at the institute.

Her study was based on an analysis of NAT2 and tobacco use in 130 patients with prostate cancer between the ages of 54 and 64 and 140 healthy men. The NAT2 enzyme is a housekeeping molecule whose function is to help detoxify potentially harmful compounds that enter the body.

Several studies outside India had earlier shown that NAT2 activity can influence susceptibility to certain cancers.

“When this enzyme is defective, it is unable to efficiently detoxify harmful compounds such as the carcinogenic chemicals that enter the body through the use of tobacco,” Mittal said.

Potential carcinogens can then bind to genetic materials in cells and trigger changes that culminate in cancer, she said. Flaws in NAT2 activity had earlier been linked to cancers of the bladder, liver, and stomach.

The Lucknow study was aimed at finding out how NAT2 influences the risk of prostate cancer among north Indians and whether its activity modulates the effect of tobacco.

Prostate cancer incidence varies worldwide. It is more common among Caucasians in the US than among Indians. Its incidence is lower among Chinese and Japanese than among Indians.

The connection between tobacco use and prostate cancer has been controversial. Several studies outside India have failed to show a consistent relationship between cigarette smoking and prostate cancer. Some studies, however, have hinted at a link between smoking and aggressive prostate cancer.