MONDAY, Dec. 22 (HealthDay News) -- A gene variation can make younger heart attack patients more prone to another heart attack, death or other heart problems if they receive the anti-clotting drug Plavix, a trio of new studies finds.

One study is published in the Dec. 23 online edition of The Lancet, while two more studies with similar results will appear in the Jan. 22 issue of the New England Journal of Medicine.

Plavix plus low-dose aspirin are often used to prevent blood vessels from clogging after a heart attack or after patients receive an artery-opening stent.

But some patients do not do well on Plavix (clopidogrel). Until now, the reasons for that variance have been unclear.

Plavix "targets a very important receptor on platelets, but people vary substantially in how good an anti-clotting effect they have" from the drug, explained Dr. Robert F. Storey, from the Cardiovascular Research Unit at the University of Sheffield School of Medicine in the United Kingdom. He is also the author of an accompanying comment in The Lancet.

"The variation in response is partly due to genetics, but there are other factors such as age which influence the response," Storey said.

For the study in The Lancet, a team led by Dr. Gilles Montalescot, from the Hopital Pitie-Salpetriere in Paris, collected data on 259 patients aged 45 and younger who suffered a first heart attack and were given Plavix.

Among these patients, 28 percent carried a gene variation called CYP2C19*2. This variation is common among the western population and even more common in Asia, the researchers noted.

During an average of a year of follow-up, patients with the gene variation were more than three-and-a-half times more likely to die, have another heart attack or require additional cardiac treatment compared to those without the variation, the researchers found.