Melatonin and dopamine serum level associations with the motor, cognitive, and sleep dysfunctions in patients with Parkinson’s disease: A cross-sectional research study

BACKGROUND Parkinson's disease (PD) is a multisystem-progressive neurodegenerative disease characterized by dopaminergic neurons, however, the role of the non-dopaminergic system (such as melatonin hormone) in the pathogenesis of PD is now emerging. OBJECTIVE To identify any potential correlation between the dopamine and melatonin serum levels, and motor, cognitive, and sleep dysfunctions in patients with PD. METHOD Cross-sectional piloting study conducted with a sample of 34 patients with PD (aged 50-72 yrs. old). Correlation tests performed to identify any potential correlations between the biomarkers' serum levels and motor, cognitive, and sleep dysfunctional levels in "on-medication" status. RESULTS Spearman's test showed significant correlations between the melatonin serum level and sleep dysfunctions including; overall sleep quality (P = 0.010) and subjective sleep quality sub-score (P = 0.001). On the other hand, spearman's test showed significant correlations between the dopamine serum level and motor dysfunctions including; Berg Balance Scale (P = 0.026), 10-Meters Walking Test (P = 0.016), and Fearing of Fall index (P = 0.007), as well between the dopamine serum level and cognitive dysfunction (P = 0.048). CONCLUSIONS Melatonin serum level would serve as a potential biomarker in understanding the PD pathogenesis, and consider the melatonin serum level in the future study related to PD besides to the dopamine serum level.