Other studies demonstrated that DDC (rs4490786), GRIN2B (rs7301328), HTR2A (rs6313), OPRK1 (rs702764), OPRM1 (rs677830), and TPH2 (rs4290270) polymorphisms were also associated with ICD in PD patients (Lee et al., 2011, 2012; Zainal Abidin et al., 2015; Erga et al., 2018; Miller et al., 2018; Li et al., 2022). This evidence concerns the gene OPRM1 and Parkinson disease.