Clopidogrel is an anti-platelet drug used to prevent clotting, which can cause heart attack or stroke. Some people are not responsive to the drug - so researchers have explored genetic mutations that may alter the enzymes involved in its activation. The cytochrome P450 enzymes have been of particular interest because of their role in drug metbolism.
However, other research surprisingly identified PON-1 (paraoxanase-1) as being involved in clopidogrel's metabolism. Then research found that the mutation of interest wasn't actually associated with responsiveness. They did, however, confirm the CYP (cytochrome P450) enzyme mutations.
Read more about the association between PON-1 and clopidogrel responsiveness.