Levodopa is commonly taken with aromatic L-amino acid decarboxylase (AADC) inhibitors like carbidopa or benserazide and catechol-O-methyltransferase (COMT) inhibitors to improve bioavailability and reduce peripheral side effects like cardiac arrhythmias, hypotension, nausea, and vomiting [8]. The gene discussed is COMT; the disease is cardiac arrhythmia.