To examine disease-related and genetic correlates of the development of psychotic symptoms in a large Parkinson's Disease (PD) population.

We studied 500 PD subjects from the NeuroGenetics Research Consortium using logistic regression models. Predictors were demographic, clinical (motor/ non-motor features) and genetic measured as continuous or dichotomous variables. Continuous measures were divided into population based tertiles.

Results are given as odds ratios (95% confidence intervals) for dichotomous variables and by ascending tertile for continuous variables. Psychotic symptoms were associated with increasing age; 4.86 (1.62-14.30), and 6.25 (2.09-18.74) (test for trend p=.01); and duration of disease 3.81 (1.23-11.76), and 5.33 (1.68-16.89) (test for trend p=.03). For non-motor features we demonstrated positive trends with depression, 1.31 (0.47-3.61), and 5.01 (2.04-12.33) (test for trend p<.0001) and cognitive dysfunction, 0.69 (0.26-1.84) and 2.51 (1.00-6.29) (test for trend p=.03), and an excess for those with sleep disorders, 2.00 (1.03-3.89) (p=.04). Psychotic symptoms were not associated with tremor or postural instability scores but there was an association with freezing of gait, 3.83 (1.67-8.75) (p<.002). Psychotic symptoms were not associated with the presence of any examined polymorphisms in the apolipoprotein, alpha-synuclein, or MAPT genes.

This is the largest study to examine correlates of psychotic symptoms in PD. We discovered a novel association with freezing of gait. We demonstrated an association with depression and duration of disease, both of which were inconsistently related in prior studies, and confirmed the association with age, cognitive dysfunction and sleep disorders.