CYP1A2has been studied in humans for its role in coffee metabolism. A Nature article explains:
"In the new study, researchers specifically tested whether caffeine in coffee could promote heart problems by examining a gene called CYP1A2. The gene, which codes for an enzyme that helps to break down caffeine, comes in two flavours: one version, known as CYP1A2*1F, metabolizes caffeine more slowly than the other."