Control vs Alzheimer's Disease: α-synuclein (CSF)


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Alpha-synuclein is a pre-synaptic protein that accumulates in Lewy bodies and Lewy neurites. The literature suggests that the concentration of α-synuclein is higher in the cerebrospinal fluid of control subjects than people with Parkinson’s disease. In contrast, in our meta-analysis of 24 eligible studies, levels of α-synuclein in the CSF were somewhat lower in control subjects than Alzheimer’s disease patients (effect size = 0.845, p = 0.0004). It should be noted that the majority of AD cases in this analysis were diagnosed according to clinical criteria alone, and therefore it is not known to what extent comorbid Lewy body pathology was present. Likewise, it is unclear to what extent comorbid AD pathology may counteract the reported reduction of α-synuclein in the CSF of PD cases.

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How to interpret a forest plot: Each individual effect size (ES) is a ratio of the mean biomarker level in one condition over the mean level in another condition. An ES equal to 1 means that the two conditions had identical mean values. An ES > 1 indicates higher levels in the first condition, whereas an ES < 1 indicates lower levels in the first condition. The overall ES, indicated by a black diamond, is a weighted average of the individual effect sizes. The weight of each data point was determined by the inverse of the variance and is reflected in the size of each square. The width of the overall ES diamond is determined by the 95 percent confidence interval. Data out of range of the scale, including ES and confidence intervals, are indicated by an arrowhead at the edge of the plot, when applicable. 

Version 3.0, July 2021.