DRD2 and Parkinson disease: The comparison of PD + ICD (49) group and PD group (36) as the internal control showed that the rs6275 substitution in the DRD2 gene suggested a correlation between the CT and CC genotypes and the PD + ICD phenotype (OR = 2.85), i.e., Allele C has a dominant mode of inheritance for the PD + ICD sample.