Gene increases risk of smoking
Scientists have discovered a gene which raises the risk of heart disease up to four times among men who smoke.
The same danger probably applies to women, although this is not yet confirmed.
Researchers made the discovery after analysing the DNA of 3052 healthy middle-aged men who were questioned about their smoking habits and monitored for eight years.
A specific variant of the gene, known as Apo-E4, was found to boost dramatically the harm done by smoking.
Smoking by itself more than doubled the risk of suffering heart attacks or blocked arteries.
But the risk for men who smoked and had Apo-E4 was nearly four times higher than it was for non-smokers with or without the gene variant.
Even after accounting for other heart disease risk factors, the risk level was almost three times higher among smokers.
Two other variants of the gene, Apo-E2 and Apo-E3, also increased smoking heart disease risk but by a much smaller degree.
E3 is the most common version of the gene, while about a quarter of the population carry the E4 variant.
E4 carriers who stopped smoking were hardly any more at risk than men who had never smoked. This showed that the smoking hazard associated with E4 could simply be removed by quitting.
Professor Steve Humphries, a British Heart Foundation expert on cardiovascular genetics at University College London, led the research.
He said "What we've found is that men who carry the E4 genotype are at high risk of heart disease, but only if they smoke.
"If you are an Apo-E4 smoker and you stop smoking, then your risk will fall off quickly."
The findings were reported in the Lancet medical journal. Prof Humphries, who has spent 20 years looking for genes linked to heart disease, acknowledged that people may now demand DNA tests to see if they have the E4 gene.
At present such tests have been confined to research laboratories and are not commercially available.
If private health companies decided to offer Apo-E tests it would raise insurance and confidentiality issues, said Prof Humphries. Providing the results would also have to be handled sensitively.
"We need to set up some pilot studies into how to tell people," said Prof Humphries. "It's a fine line between motivating people to stop smoking and scaring the pants off them."
Apo-E is a gene that appears to protect against heart disease by producing a natural protein anti-oxidant.
Prof Humphries pointed out that people could already improve their antioxidant levels by eating fresh fruits and vegetables, and taking vitamins.