Change in Plasma Levels of Amino Acid Neurotransmitters and its Correlation with Clinical Heterogeneity in Early Parkinson's Disease Patients

Summary Background The correlation between plasma amino acid (AA) neurotransmitters and clinical heterogeneity in early patients with Parkinson's disease (PD) is still poorly understood. Aims To examine the plasma levels of AA neurotransmitters in early patients with PD and to evaluate their correlation with PD subtypes. Methods Based on the predominant symptoms, fifty‐one patients with PD were enrolled and divided into four subgroups: (1) akinetic‐rigid type (ART), (2) tremor‐dominant type (TDT), (3) postural instability/gait difficulty type (PIGD), and (4) mixed type (MT). Plasma levels of AA were measured by HPLC‐RF, and their potential diagnostic practicality and their association with PD subtypes were evaluated by the receiver operating characteristic (ROC) and correlation analysis, respectively. Results Patients with PD exhibited markedly lower levels of Asp, Glu, Tau, L‐ser, and lower values of Glu/GABA ratio than healthy controls. The ROC analysis revealed their high sensitivity (77.1–87.5%) and specificity (58.8–88.2%). Furthermore, the glutamic acid (Glu), γ‐aminobutyric acid (GABA) level in the PIGD subtype was increased as compared with other subtypes and was negatively correlated with the ART/PIGD ratio. Conclusion The decrease in plasma Asp, Glu, Tau, L‐ser levels, and the value of Glu/GABA ratio may be helpful for early PD diagnosis. The elevated GABA level may be the biochemical basis for the specific symptoms of PIGD PD.