OPRM1 and Parkinson disease: 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.