Genetic variation analysis in Parkinson disease patients with and without hallucinations - Case-control study

Background: Visual hallucinations in Parkinson disease (PD) occur in approx imately one third of patients treated long-term with dopaminergic medicatio ns. In Alzheimer disease, hallucinations and psychosis have been linked to increased representations of B2/B2 homozyogotes for the dopamine receptor g ene DRD1 and 1/1 or 2/2 homozygotes for DRD3. In addition, a previous study of PD patients with and without hallucinations did not show differences in D2 and D3 polymorphisms, although careful case-control matching was not pe rformed. Another study linked the apolipoprotein E4 (APOE4) allele to hallu cinations in PD. Objective: To determine whether the frequency of dopamine receptor genetic variants and APOE alleles in patients with PD with and without chronic visu al hallucinations resembles the pattern previously documented in patients w ith Alzheimer disease. Methods: We conducted a case-control study of 44 patients with PD and chron ic hallucinations and 44 patients with PD who had never hallucinated. Cases and controls were matched for current age and medications. DNA was isolate d from blood samples and assayed for DRD1, DRD2, DRD3, DRD4, and APOE polym orphisms. Receptor polymorphisms were genotyped by polymerase chain reactio n. Genotypes in hallucinators and non-hallucinators were compared using Man tel-Haenszel tests stratified by pair, and allele frequencies were compared using Wilcoxon signed rank tests within pairs. Results: Neither D1 receptor genotypes (P = .37) nor allele frequencies (P = .38) differed, and there was no predominance of B2/B2 homozygotes in the hallucinators. For D3, there was a higher frequency of allele 2 (P = .047), but there was no significant difference between frequencies of homozygotes vs heterozygotes (P = .39) as reported in Alzheimer disease. D4 receptor d istribution of long and short alleles did not differ between the 2 patient groups, and there were too few C alleles (3 of 86) to compare D2 allele gen otypes or frequencies. For APOE, 12 cases and 12 controls carried E4 allele s (P > .99). Conclusions: With careful case-control matching, visual hallucinations in P D are not associated with the pattern seen for patients with Alzheimer dise ase and visual hallucinations. Furthermore, there was no association betwee n hallucinations and APOE. Similar methods using larger sample sizes might be adapted to test whether specific dopaminergic receptor genetic variants are associated with visual hallucinations in PD. Based on our data, the DRD 3 allele 2 may merit further study.