Kathryn A. Chung

Biomarkers are urgently needed for the diagnosis and monitoring of disease progression in Parkinson's disease. Both DJ-1 and alpha-synuclein, two proteins critically involved in Parkinson's disease pathogenesis, have been tested as disease biomarkers in several recent studies with inconsistent results. These have been largely due to variation in the protein species detected by different antibodies, limited numbers of patients in some studies, or inadequate control of several important variables. In this study, the nature of DJ-1 and alpha-synuclein in human cerebrospinal fluid was studied by a combination of western blotting, gel filtration and mass spectrometry. Sensitive and quantitative Luminex assays detecting most, if not all, species of DJ-1 and alpha-synuclein in human cerebrospinal fluid were established. Cerebrospinal fluid concentrations of DJ-1 and alpha-synuclein from 117 patients with Parkinson's disease, 132 healthy individuals and 50 patients with Alzheimer's disease were analysed using newly developed, highly sensitive Luminex technology while controlling for several major confounders. A total of 299 individuals and 389 samples were analysed. The results showed that cerebrospinal fluid DJ-1 and alpha-synuclein levels were dependent on age and influenced by the extent of blood contamination in cerebrospinal fluid. Both DJ-1 and alpha-synuclein levels were decreased in Parkinson's patients versus controls or Alzheimer's patients when blood contamination was controlled for. In the population aged > or = 65 years, when cut-off values of 40 and 0.5 ng/ml were chosen for DJ-1 and alpha-synuclein, respectively, the sensitivity and specificity for patients with Parkinson's disease versus controls were 90 and 70% for DJ-1, and 92 and 58% for alpha-synuclein. A combination of the two markers did not enhance the test performance. There was no association between DJ-1 or alpha-synuclein and the severity of Parkinson's disease. Taken together, this represents the largest scale study for DJ-1 or alpha-synuclein in human cerebrospinal fluid so far, while using newly established sensitive Luminex assays, with controls for multiple variables. We have demonstrated that total DJ-1 and alpha-synuclein in human cerebrospinal fluid are helpful diagnostic markers for Parkinson's disease, if variables such as blood contamination and age are taken into consideration.

OBJECTIVE: There is a clear need to develop biomarkers for Parkinson disease (PD) diagnosis, differential diagnosis of Parkinsonian disorders, and monitoring disease progression. We and others have demonstrated that a decrease in DJ-1 and/or α-synuclein in the cerebrospinal fluid (CSF) is a potential index for Parkinson disease diagnosis, but not for PD severity. METHODS: Using highly sensitive and quantitative Luminex assays, we measured total tau, phosphorylated tau, amyloid beta peptide 1-42 (Aβ(1-42)), Flt3 ligand, and fractalkine levels in CSF in a large cohort of PD patients at different stages as well as healthy and diseased controls. The utility of these 5 markers was evaluated for disease diagnosis and severity/progression correlation alone, as well as in combination with DJ-1 and α-synuclein. The major results were further validated in an independent cohort of cross-sectional PD patients as well as in PD cases with CSF samples collected longitudinally. RESULTS: The results demonstrated that combinations of these biomarkers could differentiate PD patients not only from normal controls but also from patients with Alzheimer disease (AD) and multiple system atrophy. Particularly, with CSF Flt3 ligand, PD could be clearly differentiated from multiple system atrophy, a disease that overlaps with PD clinically, with excellent sensitivity (99%) and specificity (95%). In addition, we identified CSF fractalkine/Aβ(1-42) that positively correlated with PD severity in cross-sectional samples as well as with PD progression in longitudinal samples. INTERPRETATION: We have demonstrated that this panel of 7 CSF proteins could aid in Parkinson disease diagnosis, differential diagnosis, and correlation with disease severity and progression.

OBJECTIVE: To test for an association between the apolipoprotein E (APOE) ϵ4 allele and dementias with synucleinopathy. DESIGN: Genetic case-control association study. SETTING: Academic research. PATIENTS: Autopsied subjects were classified into 5 categories: dementia with high-level Alzheimer disease (AD) neuropathologic changes (NCs) but without Lewy body disease (LBD) NCs (AD group; n=244), dementia with LBDNCs and high-level ADNCs (LBD-AD group; n=224), dementia with LBDNCs and no or low levels of ADNCs (pure DLB [pDLB] group; n=91), Parkinson disease dementia (PDD) with no or low levels of ADNCs (n=81), and control group (n=269). MAIN OUTCOME MEASURE The APOE allele frequencies. RESULTS The APOE ϵ4 allele frequency was significantly higher in the AD (38.1%), LBD-AD (40.6%), pDLB (31.9%), and PDD (19.1%) groups compared with the control group (7.2%; overall χ(2)(4)=185.25; P=5.56 × 10(-39)), and it was higher in the pDLB group than the PDD group (P= .01). In an age-adjusted and sex-adjusted dominant model, ϵ4 was strongly associated with AD (odds ratio, 9.9; 95% CI, 6.4-15.3), LBD-AD (odds ratio, 12.6; 95% CI, 8.1-19.8), pDLB (odds ratio, 6.1; 95% CI, 3.5-10.5), and PDD (odds ratio, 3.1; 95% CI, 1.7-5.6). CONCLUSIONS The APOE ϵ4 allele is a strong risk factor across the LBD spectrum and occurs at an increased frequency in pDLB relative to PDD. This suggests that ϵ4 increases the likelihood of presenting with dementia in the context of a pure synucleinopathy. The elevated ϵ4 frequency in the pDLB and PDD groups, in which the overall brain neuritic plaque burden was low, indicates that apoE might contribute to neurodegeneration through mechanisms unrelated to amyloid processing.

Phosphorylated α-synuclein (PS-129), a protein implicated in the pathogenesis of Parkinson's disease (PD), was identified by mass spectrometry in human cerebrospinal fluid (CSF). A highly sensitive and specific assay was established and used to measure PS-129 together with total α-synuclein in the CSF of patients with PD, other parkinsonian disorders such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), and healthy individuals (a total of ~600 samples). PS-129 CSF concentrations correlated weakly with PD severity and, when combined with total α-synuclein concentrations in CSF, contributed to distinguishing PD from MSA and PSP. Further rigorous validation in independent cohorts of patients, especially those where samples have been collected longitudinally, will determine whether the concentration of PS-129 in CSF will be useful for diagnosing PD and for monitoring PD severity and progression.

The therapeutic imperative for Alzheimer disease (AD) and Parkinson disease (PD) calls for discovery and validation of biomarkers. Increased cerebrospinal fluid (CSF) tau and decreased amyloid (A) beta42 have been validated as biomarkers of AD. In contrast, there is no validated CSF biomarker for PD. We validated our proteomics-discovered multianalyte profile (MAP) in CSF from 95 control subjects, 48 patients with probable AD, and 40 patients with probable PD. An optimal 8-member MAP agreed with expert diagnosis for 90 control subjects (95%), 36 patients with probable AD (75%), and 38 patients with probable PD (95%). This MAP consisted of the following (in decreasing order of contribution): tau, brain-derived neurotrophic factor, interleukin 8, Abeta42, beta2-microglobulin, vitamin D binding protein, apolipoprotein (apo) AII, and apoE. This first large-scale validation of a proteomic-discovered MAP suggests a panel of 8 CSF proteins that are highly effective at identifying PD and moderately effective at identifying AD.