Dopamine plays a critical role in disease pathology of Parkinson’s disease and schizophrenia. These two neurological disorders represent the disease end points of dopaminergic deficit and hyperactivity, respectively in mid-brain. Current pharmacological treatment strategies aim to restore normal dopamine levels. However, during treatment the patients develop adverse effects due to overshooting of normal dopamine levels leading to psychosis in Parkinson’s disease and extra-pyramidal symptoms in schizophrenia. In absence of any laboratory tests, clinicians fail to recognize low, high, and physiological levels of mid-brain dopamine, thereby leading to decreased patient compliance.  

Drug-naïve Parkinson’s disease patients, Parkinson’s disease patients treated with dopaminergic therapy, neurological controls, schizophrenic patients treated with anti-dopaminergic therapy, and drug-naïve schizophrenic patients were recruited for the study and CSF was collected. ELISA was carried out for apolipoprotein E and α-synuclein in the CSF samples. Pathway analysis and correlation studies were done for these two proteins.  

Apolipoprotein E and α-synuclein CSF concentrations have an inverse correlation along the entire dopaminergic clinical spectrum. Each protein by itself or as a combination has encouraging sensitivity of 79.3% and specificity of 93.3% to differentiate Parkinson’s disease and schizophrenia from neurological controls, respectively. Pathway analysis provides detailed interactions of these proteins and the proposed molecular events at neuronal synapse helps to provide plausible rational for their differential expression along the dopaminergic spectrum.