By using this approach, we replicated, to our knowledge for the first time, a previously reported association in the opioid receptor gene OPRM1, where in 92 adult-onset PD patients who had been taking levodopa at least 5 years and/or had developed levodopa-induced dyskinesia, carrying the G-allele of the rs1799971 A118G single nucleotide coding region polymorphism of the mu opioid receptor was independently associated with increased risk of earlier onset of dyskinesia8. This evidence concerns the gene OPRM1 and drug-induced dyskinesia.