Kathryn A. Chung

DJ-1 and α-synuclein in human cerebrospinal fluid as biomarkers of Parkinson's disease

Biomarkers are urgently needed for the diagnosis and monitoring of disease progression in Parkinsons disease. Both DJ-1 and alpha-synuclein, two proteins critically involved in Parkinsons 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 Parkinsons disease, 132 healthy individuals and 50 patients with Alzheimers 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 Parkinsons patients versus controls or Alzheimers 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 Parkinsons 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 Parkinsons 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 Parkinsons disease, if variables such as blood contamination and age are taken into consideration.

Cerebrospinal Fluid Biomarkers for Parkinson Disease Diagnosis and Progression

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.

CSF Multianalyte Profile Distinguishes Alzheimer and Parkinson Diseases

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.

Effects of a central cholinesterase inhibitor on reducing falls in Parkinson disease

Objective: To investigate if a central cholinesterase inhibitor will reduce falling frequency in subjects with Parkinson disease (PD) with advanced postural instability. Background: Falling due to postural instability is a significant problem in advancing PD, and is minimally impacted by dopaminergic therapy. Anticholinergic medications increase falling in the elderly. Further, CNS cholinergic neuron loss occurs in PD. We hypothesized that acetylcholine augmentation may reduce frequent falling in subjects with PD. Methods: We enrolled 23 subjects with PD who reported falling or nearly falling more than 2 times per week. In a randomized, placebo-controlled, crossover design, subjects were given 6 weeks of donepezil or placebo with a 3-week washout between phases. The primary outcomes were daily falls and near falls reported on postcards. Secondary outcomes included scores on the Activities of Balance Confidence Scale, Berg Balance Scale, Clinical Global Impression of Change, Folstein Mini-Mental State Examination, and the motor section of the Unified Parkinsons Disease Rating Scale. Results: Fall frequency per day on placebo was 0.25 ± 0.08 (SEM) compared with 0.13 ± 0.03 on donepezil (p < 0.05). The frequency of near falls was not significantly different between phases. The secondary outcomes did not differ; however, there was a trend to improvement on the subject-completed Global Impression of Change scale. Conclusions: Subjects with PD fell approximately half as often during the 6 weeks on donepezil than on placebo. Larger trials of cholinergic augmentation are warranted in subjects with PD with frequent falls. Classification of evidence: This study provides Class II evidence that donepezil (maximum 10 mg per day) significantly reduced the number of falls in patients with PD (0.13 falls/day, SEM = 0.03) than when taking placebo (0.25 falls/day, SEM = 0.08, p = 0.049).

CSF Aβ42 and tau in Parkinson's disease with cognitive impairment

We tested the hypothesis that the CSF biomarker signature associated with Alzheimers disease (AD) is present in a subset of individuals with Parkinsons disease and Dementia (PD‐D) or with PD and Cognitive Impairment, Not Dementia (PD‐CIND). We quantified CSF Aβ42, total tau (T‐tau), and phospho‐tau (P181‐tau) using commercially available kits. Samples were from 345 individuals in seven groups (n): Controls ≤50 years (35), Controls >50 years (115), amnestic Mild Cognitive Impairment (aMCI) (24), AD (49), PD (49), PD‐CIND (62), and PD‐D (11). We observed expected changes in AD or aMCI compared with age‐matched or younger controls. CSF Aβ42 was reduced in PD‐CIND (P < 0.05) and PD‐D (P < 0.01), whereas average CSF T‐tau and P181‐tau were unchanged or decreased. One‐third of PD‐CIND and one‐half of PD‐D patients had the biomarker signature of AD. Abnormal metabolism of Aβ42 may be a common feature of PD‐CIND and PD‐D.

Impaired olfaction and other prodromal features in the Parkinson At-Risk Syndrome Study.

To test the association between impaired olfaction and other prodromal features of PD in the Parkinson At‐Risk Syndrome Study. The onset of olfactory dysfunction in PD typically precedes motor features, suggesting that olfactory testing could be used as a screening test. A combined strategy that uses other prodromal nonmotor features, along with olfactory testing, may be more efficient than hyposmia alone for detecting the risk of PD. Individuals with no neurological diagnosis completed a mail survey, including the 40‐item University of Pennsylvania Smell Identification Test, and questions on prodromal features of PD. The frequency of reported nonmotor features was compared across individuals with and without hyposmia. A total of 4,999 subjects completed and returned the survey and smell test. Of these, 669 were at or below the 15th percentile based on age and gender, indicating hyposmia. Hyposmics were significantly more likely to endorse nonmotor features, including anxiety and depression, constipation, and rapid eye movement sleep behavior disorder symptoms, and to report changes in motor function. Twenty‐six percent of subjects with combinations of four or more nonmotor features were hyposmic, compared to 12% for those reporting three or fewer nonmotor features (P < 0.0001). Hyposmia is associated with other nonmotor features of PD in undiagnosed individuals. Further assessment of hyposmic subjects using more specific markers for degeneration, such as dopamine transporter imaging, will evaluate whether combining hyposmia and other nonmotor features is useful in assessing the risk of future neurodegeneration.

SNCA Variant Associated With Parkinson Disease and Plasma α-Synuclein Level

BACKGROUND A functional repeat polymorphism in the SNCA promoter (REP1) conveys susceptibility for Parkinson disease (PD). There is also increasing evidence that single-nucleotide polymorphisms (SNPs) elsewhere in the gene are associated with PD risk. OBJECTIVES To further explore the association of common SNCA SNPs with PD susceptibility, to determine whether evidence of allelic heterogeneity exists, and to examine the correlation between PD-associated variants and plasma α-synuclein levels. DESIGN Two-tiered analysis. SETTING Academic research. PATIENTS Patients and control subjects from the NeuroGenetics Research Consortium. MAIN OUTCOME MEASURES We performed a 2-tiered analysis of 1956 patients with PD and 2112 controls from the NeuroGenetics Research Consortium using a comprehensive tag SNP approach. Previously published REP1 genotypes were also included. Plasma α-synuclein was assayed in 86 patients with PD and 78 controls using a highly sensitive Luminex assay. RESULTS Five of 15 SNPs genotyped were associated with PD under an additive model in tier 1 (α = .05). Of these, 4 were successfully replicated in tier 2. In the combined sample, the most significant marker was rs356219 (odds ratio, 1.41; 95% confidence interval, 1.28-1.55; P = 1.6 × 10(-12)), located approximately 9 kilobases downstream from the gene. A regression model containing rs356219 alone best fit the data. The linkage disequilibrium correlation coefficient between this SNP and REP1 was low (r(2) = 0.09). The risk-associated C allele of rs356219 was also correlated with higher transformed plasma α-synuclein levels in patients under an adjusted additive model (P = .005). CONCLUSIONS Our data suggest that 1 or more unidentified functional SNCA variants modify risk for PD and that the effect is larger than and independent of REP1. This variant(s), tagged by rs356219, might act by upregulating SNCA expression in a dose-dependent manner.

Phosphorylated α-Synuclein in Parkinson’s Disease

An assay for detecting phosphorylated α-synuclein in CSF may help to diagnose Parkinson’s disease and determine disease severity. Tracking the Course of Neurodegeneration Parkinson’s disease (PD), a neurodegenerative disorder characterized by loss of motor function, affects millions of people worldwide. Although there are drugs that can replace dopamine and thus compensate for the loss of dopaminergic neurons of the nigrostriatal pathway, there is no treatment that can prevent neuronal degeneration. A big goal has been to discover biomarkers that could be used to distinguish PD from other parkinsonian disorders, such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), and to follow disease progression. To date, one of the most extensively tested markers is α-synuclein, a protein that has been implicated in the pathogenesis of PD. There is a decrease in the concentration of α-synuclein in the cerebrospinal fluid (CSF) of patients with PD compared to healthy individuals. However, α-synuclein does not appear to be useful in terms of differentiating PD from other parkinsonian disorders with overlapping symptoms and does not correlate with PD severity or progression. Now, Wang and colleagues have identified an isoform of α-synuclein, phosphorylated α-synuclein (PS-129), in human CSF that may prove to be a more useful marker of PD than α-synuclein. First, the authors developed a highly sensitive and specific assay to measure PS-129 concentrations as well as total α-synuclein in CSF samples from healthy individuals and from a cohort of patients with PD, MSA, PSP, and Alzheimer’s disease. The authors discovered that the PS-129 concentration in CSF, when combined with the total α-synuclein concentration in CSF, helped to distinguish PD patients from those with MSA and PSP. Additionally, CSF PS-129 concentrations in CSF correlated with disease severity in PD patients. These early results suggest that PS-129 may be useful as a marker to assist in the differential diagnosis of PD and to monitor disease progression. This would be of value for selecting patients for clinical trials to test new PD-modifying therapies as they become available and to monitor disease in response to these treatments. However, before PS-129 can be deployed as a marker for PD, it will need to be validated in independent cohorts of PD patients, especially those with samples collected longitudinally. 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.

Significance and confounders of peripheral DJ-1 and alpha-synuclein in Parkinson's disease.

DJ-1 and alpha-synuclein are leading biomarkers for Parkinsons disease diagnosis and/or monitoring disease progression. A few recent investigations have determined DJ-1 and alpha-synuclein levels in plasma or serum, a more convenient sample source than cerebrospinal fluid; but the results were variable or even contradictory. Besides limitations in detection technology and limited number of cases in some studies, inadequate control of several important confounders likely has contributed to these inconsistent results. In this study, the relative contribution of each blood component to blood DJ-1 and alpha-synuclein was evaluated, followed by quantification of plasma levels of both markers in a larger cohort of patients/subjects ( approximately 300 cases) whose cerebrospinal fluid DJ-1 and alpha-synuclein levels have been determined recently. The results demonstrated that the DJ-1 and alpha-synuclein in blood resided predominantly in red blood cells (>95%), followed by platelets (1-4%), white blood cells and plasma (< or =1%), indicating that variations in hemolysis and/or platelet contamination could have a significant effect on plasma/serum DJ-1 and alpha-synuclein levels. Nonetheless, after adjusting for the age, although there was a trend of decrease in DJ-1 and alpha-synuclein in patients with Parkinsons or Alzheimers disease compared with healthy controls, no statistical difference was observed in this cohort between any groups, even when the extent of hemolysis and platelet contamination were controlled for. Additionally, no correlation between DJ-1 or alpha-synuclein and Parkinsons disease severity was identified. In conclusion, unlike in cerebrospinal fluid, total DJ-1 or alpha-synuclein in plasma alone is not useful as biomarkers for Parkinsons disease diagnosis or progression/severity.

GBA Variants are associated with a distinct pattern of cognitive deficits in Parkinson's disease

Loss‐of‐function mutations in the GBA gene are associated with more severe cognitive impairment in PD, but the nature of these deficits is not well understood and whether common GBA polymorphisms influence cognitive performance in PD is not yet known.