DOCK3 and Mental deterioration: Backward elimination regression analysis for cognitive decline defined by Level 1 revealed the following predictors: age of onset [hazard ratio (HR) 1.03, 95% confidence interval (CI) 1.01–1.06; Wald 6.75 P = 0.009], MDS-UPDRS Part-III (HR 1.03, 95% CI 1.00–1.05; Wald 5.20; P = 0.023), Semantic Fluency Test (HR 0.98, 95% CI 0.96–1.00; Wald 4.03; P = 0.045), Symbol Digit Modalities Test (HR 0.98, 95% CI 0.95–0.99; Wald 4.18; P = 0.041), Hopkin’s Learning Verbal Test-Revised Recall (HR 0.972, 95% CI 0.954–0.991; Wald: 8.18 P = 0.004) and MoCA (HR 0.81, 95% CI 0.70–0.95; Wald 7.00; P = 0.008).