Relation of risk factors and putative premotor markers for Parkinson’s disease

Who to Enroll in Parkinson Disease Prevention Trials? The Case for Composite Prodromal Cohorts

Significant progress has been made in expanding our understanding of prodromal Parkinson disease (PD), particularly for recognition of early motor and nonmotor signs and symptoms. Although identification of these prodromal features may improve our understanding of the earliest stages of PD, they are individually insufficient for early disease detection and enrollment of participants in prevention trials in most cases because of low sensitivity, specificity, and positive predictive value. Composite cohorts, composed of individuals with multiple co-occurring prodromal features, are an important resource for conducting prodromal PD research and eventual prevention trials because they are more representative of the population at risk for PD, allow investigators to evaluate the efficacy of an intervention across individuals with varying prodromal feature patterns, are able to produce larger sample sizes, and capture individuals at different stages of prodromal PD. A key challenge in identifying individuals with prodromal disease for composite cohorts and prevention trial participation is that we know little about the natural history of prodromal PD. To move toward prevention trials, it is critical that we better understand common prodromal feature patterns and be able to predict the probability of progression and phenoconversion. Ongoing research in cohort studies and administrative databases is beginning to address these questions, but further longitudinal analyses in a large population-based sample are necessary to provide a convincing and definitive strategy for identifying individuals to be enrolled in a prevention trial.

Modeling Parkinson's disease-related symptoms in alpha-synuclein overexpressing mice

BACKGROUND

Intracellular deposition of alpha-synuclein (α-syn) as Lewy bodies and Lewy neurites is a central event in the pathogenesis of Parkinson's disease (PD) and other α-synucleinopathies. Transgenic mouse models overexpressing human α-syn, are useful research tools in preclinical studies of pathogenetic mechanisms. Such mice develop α-syn inclusions as well as neurodegeneration with a topographical distribution that varies depending on the choice of promoter and which form of α-syn that is overexpressed. Moreover, they display motor symptoms and cognitive disturbances that to some extent resemble the human conditions.

PURPOSE

One of the main motives for assessing behavior in these mouse models is to evaluate the potential of new treatment strategies, including their impact on motor and cognitive symptoms. However, due to a high within-group variability with respect to such features, the behavioral studies need to be applied with caution. In this review, we discuss how to make appropriate choices in the experimental design and which tests that are most suitable for the evaluation of PD-related symptoms in such studies.

METHODS

We have evaluated published results on two selected transgenic mouse models overexpressing wild type (L61) and mutated (A30P) α-syn in the context of their validity and utility for different types of behavioral studies.

CONCLUSIONS

By applying appropriate behavioral tests, α-syn transgenic mouse models provide an appropriate experimental platform for studies of symptoms related to PD and other α-synucleinopathies.

Depressive disorders in the elderly and dementia: An update

The relationship between depressive disorders in the elderly and dementia, particularly Alzheimer’s disease (AD), is highly complex. While the nature of this relationship is still a matter of debate, differential diagnosis and treatment remain a great clinical challenge. We review recent findings on the conundrum of depressive disorders in the elderly and AD. There is a biological continuum between depressive disorders in the elderly – or at least a subgroup of them – and AD. While elderly subjects with depression and patients with AD exhibit higher circulating levels of pro-inflammatory molecules and lower BDNF than matched controls, CSF levels of Aβ42 can discriminate AD from depressive disorders in the elderly. The role of antidepressant treatment as a strategy to minimize the risk of AD remains to be established.

Diagnostic biomarkers for Parkinson's disease at a glance: where are we?

Parkinson's disease (PD) is a neurodegenerative disorder whose aetiology remains unclear: degeneration involves several neurotransmission systems, resulting in a heterogeneous disease characterized by motor and non-motor symptoms. PD causes progressive disability that responds only to symptomatic therapies. Future advances include neuroprotective strategies for use in at-risk populations before the clinical onset of disease, hence the continuing need to identify reliable biomarkers that can facilitate the clinical diagnosis of PD. In this evaluative review, we summarize information on potential diagnostic biomarkers for use in the clinical and preclinical stages of PD.

Cognitive and Neuropsychiatric Features of Early Parkinson's Disease

The clinical definition of Parkinson's disease (PD) is based on cardinal motor features including bradykinesia as well as an additional symptom of tremor, postural instability, or rigidity. Evidence from neuropathological, imaging, and clinical research suggests a premotor, early phase of PD pathology. Further understanding of the earliest biomarkers of PD is crucial for the development of neuroprotective, disease modifying, cognitive, and psychiatric interventions. Recent research has explored early non-motor markers of PD pathology. This issue is especially timely as the International Parkinson and Movement Disorder Society has recently provided a research definition for prodromal PD which includes combinations of prodromal markers and risk factors aimed at identifying target populations for disease-prevention trials. In this review of early PD, we will outline early non-motor symptoms, early cognitive and neuropsychiatric features, neuropsychological assessment strategies, emerging evidence for early biomarkers, and treatment recommendations.

Autonomic Dysfunction in Early Parkinson's Disease: Results from the United Kingdom Tracking Parkinson's Study

BACKGROUND

Autonomic dysfunction is common in the later stages of Parkinson's disease (PD), but less is known about its presence and severity in early disease.

OBJECTIVE

To analyze features of autonomic dysfunction in recent onset PD cases, and their relationship to motor severity, medication use, other nonmotor symptoms (NMS), and quality-of-life scores.

METHODS

Detailed patient-reported symptoms of autonomic dysfunction were assessed in a multicenter cohort study in PD cases that had been diagnosed within the preceding 3.5 years.

RESULTS

There were 1746 patients (1132 males, 65.2%), mean age 67.6 years (SD 9.3), mean disease duration 1.3 years (SD 0.9), mean Movement Disorder Society Unified Parkinson's Disease Rating Scale motor score 22.5 (SD 12.1). Orthostatic symptoms were reported by 39.6%, male erectile dysfunction by 56.1%, and female anorgasmia by 57.4%. Sialorrhea was an issue in 51.4% of patients, constipation in 43.6%, and dysphagia in 20.1%. Autonomic features increased with higher modified Hoehn and Yahr stages (P < 0.001). The severity of autonomic dysfunction was associated with the postural instability gait difficulty motor phenotype [β-coefficient 1.7, 95% confidence interval (CI) 0.7, 2.6, P < 0.001], depression (β-coefficient 4.1, CI 3.0, 5.2, P < 0.001), and excess daytime sleepiness (β-coefficient 3.1, CI 1.9, 4.2, P < 0.001). Dopamine agonists were the only drug class associated with greater autonomic dysfunction (P = 0.019). The severity of autonomic dysfunction strongly correlated with the presence of other NMS (ρ = 0.717, P < 0.001), and with poorer quality-of-life scores (ρ = 0.483, P < 0.001).

CONCLUSIONS

Autonomic dysfunction is common in early PD. Autonomic dysfunction correlates with the presence of other NMS, and with worse quality of life.

Succinobucol, a Non-Statin Hypocholesterolemic Drug, Prevents Premotor Symptoms and Nigrostriatal Neurodegeneration in an Experimental Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by non-motor and motor disabilities. This study investigated whether succinobucol (SUC) could mitigate nigrostriatal injury caused by intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in mice. Moreover, the effects of SUC against MPTP-induced behavioral impairments and neurochemical changes were also evaluated. The quantification of tyrosine hydroxylase-positive (TH⁺) cells was also performed in primary mesencephalic cultures to evaluate the effects of SUC against 1-methyl-4-phenylpyridinium (MPP⁺) toxicity in vitro. C57BL/6 mice were treated with SUC (10 mg/kg/day, intragastric (i.g.)) for 30 days, and thereafter, animals received MPTP infusion (1 mg/nostril) and SUC treatment continued for additional 15 days. MPTP-infused animals displayed significant non-motor symptoms including olfactory and short-term memory deficits evaluated in the olfactory discrimination, social recognition, and water maze tasks. These behavioral impairments were accompanied by inhibition of mitochondrial NADH dehydrogenase activity (complex I), as well as significant decrease of TH and dopamine transporter (DAT) immunoreactivity in the substantia nigra pars compacta and striatum. Although SUC treatment did not rescue NADH dehydrogenase activity inhibition, it was able to blunt MPTP-induced behavioral impairments and prevented the decrease in TH and DAT immunoreactivities in substantia nigra (SN) and striatum. SUC also suppressed striatal astroglial activation and increased interleukin-6 levels in MPTP-intoxicated mice. Furthermore, SUC significantly prevented the loss of TH⁺ neurons induced by MPP⁺ in primary mesencephalic cultures. These results provide new evidence that SUC treatment counteracts early non-motor symptoms and neurodegeneration/neuroinflammation in the nigrostriatal pathway induced by intranasal MPTP administration in mice by modulating events downstream to the mitochondrial NADH dehydrogenase inhibition.

Neuropathobiology of non-motor symptoms in Parkinson disease

Parkinson disease (PD) is a multisystem disorder associated with α-synuclein aggregates throughout the central, autonomic, and peripheral nervous system, clinically characterized by motor and non-motor (NM) symptoms. The NMS in PD, many of which antedating motor dysfunction and representing a preclinical phase spanning 20 or more years, are linked to widespread distribution of α-synuclein pathology not restricted to the dopaminergic nigrostriatal system that is responsible for core motor features of PD. The pathologic substrate of NM manifestations such as olfactory, autonomic (gastrointestinal, urogenital, cardia, respiratory), sensory, skin, sleep, visual, neuropsychiatric dysfunctions (cognitive, mood, dementia), and others are critically reviewed. In addition to non-nigral brainstem nuclei, α-synuclein pathology involves sympathetic and parasympathetic, enteric, cardiac and pelvic plexuses, and many other organs indicating a topographical and chronological spread, particularly in the prodromal stages of the disease. Few animal models recapitulate NMS in PD. The relationship between regional α-synuclein/Lewy pathology, neurodegeneration and the corresponding clinical deficits awaits further elucidation. Controlled clinicopathologic studies will refine the correlations between presymptomatic and late-developing NM features of PD and neuropathology, and new premotor biomarkers will facilitate early diagnosis of PD as a basis for more effective preventive and therapeutic options of this devastating disease.

Evolution of prodromal clinical markers of Parkinson disease in a GBA mutation-positive cohort

IMPORTANCE

Numerically, the most important genetic risk factor for the development of Parkinson disease (PD) is the presence of a glucocerebrosidase gene (GBA) mutation.

OBJECTIVE

To evaluate longitudinally and clinically a GBA mutation-positive cohort and the evolution of the prodromal features of PD.

DESIGN, SETTING, AND PARTICIPANTS

Participants in a study of the etiology and prodrome of PD were reevaluated in this clinic-based 2-year follow-up report. Patients with type 1 Gaucher disease (GD) and heterozygous GBA mutation carriers were recruited in 2010 from the Lysosomal Storage Disorder Unit at the Royal Free Hospital, London, England. Thirty patients who previously received a diagnosis of type 1 GD, 28 heterozygous GBA mutation carriers, and 26 genetically unrelated controls were included. Exclusion criteria included a diagnosis of PD or dementia for both the patients with GD and the GBA mutation carriers and any existing neurological disease for the controls.

MAIN OUTCOMES AND MEASURES

Assessment was performed for clinical markers using standardized scales for hyposmia, rapid eye movement sleep behavior disorder, depression, autonomic dysfunction, cognitive function, and parkinsonian motor signs (using the Unified Parkinson's Disease Rating Scale motor subscale [UPDRS part III]).

RESULTS

Over 2 years, depression scores were significantly worse for heterozygous carriers (mean baseline, 0.65; mean follow-up, 2.88; P = .01), rapid eye movement sleep behavior disorder scores were significantly worse for patients with GD (mean baseline, 0.93; mean follow-up, 2.93; P < .001) and heterozygotes (mean baseline, 0.10; mean follow-up, 2.30; P < .001), and UPDRS part III scores were significantly worse for patients with GD (mean baseline, 4.29; mean follow-up, 7.82; P < .001) and heterozygotes (mean baseline, 1.97; mean follow-up, 4.50; P < .001). For controls, there was a small but significant deterioration in the UPDRS part II (activities of daily living) score (mean baseline, 0.00; mean follow-up, 0.58; P = .006). At 2 years, olfactory and cognitive assessment scores were lower in patients with GD and heterozygotes compared with controls, but they did not differ significantly from baseline. When the results from the patients with GD and the heterozygotes were combined, a significant deterioration from baseline was observed, as reflected in the Rapid Eye Movement Sleep Behaviour Disorder Questionnaire (mean baseline, 0.51; mean follow-up, 2.63; P < .001), Beck Depression Inventory (mean baseline, 1.72; mean follow-up, 4.44; P = .002), and UPDRS part II (mean baseline, 0.88; mean follow-up, 2.01; P < .001) and part III scores (mean baseline, 3.09; mean follow-up, 6.10; P < .001) (all P < .01), and at 2 years, significant differences in University of Pennsylvania Smell Identification Test, Unified Multiple System Atrophy Rating Scale, Mini-Mental State Examination, Montreal Cognitive Assessment, and UPDRS part II and part III scores were observed between patients with GD/heterozygotes and controls (all P < .05).

CONCLUSIONS AND RELEVANCE

This study indicates that, as a group, GBA mutation-positive individuals show a deterioration in clinical markers consistent with the prodrome of PD. Within this group of individual, 10% appear to be evolving at a more rapid rate.

Prediction of Parkinson's disease subsequent to severe depression: a ten-year follow-up study

Major depressive disorder (MDD) has been associated with an increased risk of subsequent Parkinson's disease (PD) in case-control and cohort studies. However, depression alone is unlikely to be a useful marker of prodromal PD due to its low specificity. In this longitudinal observational study, we assessed whether the presence of other potential markers of prodromal PD predicts the subsequent development of PD in MDD patients. Of 57 patients with severe MDD but no diagnosis of PD who underwent a structured interview, olfactory and motor investigation and transcranial sonography at baseline, 46 (36 women; mean age 54.9 ± 11.7 years) could be followed for up to 11 (median, 10) years. Three patients (2 women; age 64, 65 and 70 years) developed definite PD after 1, 7, and 9 years, respectively. The combined finding of mild asymmetric motor slowing, idiopathic hyposmia, and substantia nigra hyperechogenicity predicted subsequent PD in all patients who could be followed for longer than 1 year. Out of the whole study cohort, only the subjects with subsequent PD presented with the triad of asymmetric motor slowing, idiopathic hyposmia, and substantia nigra hyperechogenicity in combination with at least two out of four reportable risk factors (family history of PD, current non-smoker, non-coffee drinker, constipation) at baseline investigation. Post-hoc analysis revealed that additional rating of eye and eye-lid motor abnormalities might further improve the prediction of PD in larger cohorts. Findings of this pilot-study suggest that MDD patients at risk of subsequent PD can be identified using an inexpensive non-invasive diagnostic battery.

Prodromal features for Parkinson's disease--baseline data from the TREND study

BACKGROUND AND PURPOSE

A number of non-motor features are known to precede motor manifestations of Parkinson's disease (PD). They are supposed to already represent the prodromal neurodegenerative state in those who later develop PD and are thus called prodromal markers. In this study, three prodromal markers, depression, rapid eye movement behaviour disorder (RBD) and hyposmia, were selected and were related to other prodromal features in elderly individuals without PD.

METHODS

From the Tübinger Evaluation of Risk Factors for Early Detection of Neurodegeneration (TREND) study, 698 healthy individuals aged 50-80 years reporting one or more of the selected prodromal markers (SPMs), but without neurodegenerative disorders, were evaluated and classified according to the status of prodromal markers. Other prodromal PD-related features were assessed with a 23-item questionnaire and compared between participants with and without the three SPMs.

RESULTS

Individuals with the SPMs for PD endorsed more of the additional possible prodromal features of PD than those without; of 23 possible prodromal features, the median number identified amongst participants with no SPMs was two, compared with four with one marker, five with two and seven with three (P < 0.001). Regarding individual SPMs, participants with depression and RBD endorsed five of 23 markers, compared with three for those with hyposmia (P = 0.001). There was no significant increase in the number of prodromal features amongst those with two SPMs compared with those with only one marker.

CONCLUSIONS

Individuals with the SPMs for PD report a higher prevalence of other prodromal PD symptoms. This may indicate that these markers can identify individuals at risk for PD.

Biomarkers in Parkinson's disease (recent update)

Parkinson's disease (PD) is the second most common neurodegenerative disorder mostly affecting the aging population over sixty. Cardinal symptoms including, tremors, muscle rigidity, drooping posture, drooling, walking difficulty, and autonomic symptoms appear when a significant number of nigrostriatal dopaminergic neurons are already destroyed. Hence we need early, sensitive, specific, and economical peripheral and/or central biomarker(s) for the differential diagnosis, prognosis, and treatment of PD. These can be classified as clinical, biochemical, genetic, proteomic, and neuroimaging biomarkers. Novel discoveries of genetic as well as nongenetic biomarkers may be utilized for the personalized treatment of PD during preclinical (premotor) and clinical (motor) stages. Premotor biomarkers including hyper-echogenicity of substantia nigra, olfactory and autonomic dysfunction, depression, hyposmia, deafness, REM sleep disorder, and impulsive behavior may be noticed during preclinical stage. Neuroimaging biomarkers (PET, SPECT, MRI), and neuropsychological deficits can facilitate differential diagnosis. Single-cell profiling of dopaminergic neurons has identified pyridoxal kinase and lysosomal ATPase as biomarker genes for PD prognosis. Promising biomarkers include: fluid biomarkers, neuromelanin antibodies, pathological forms of α-Syn, DJ-1, amyloid β and tau in the CSF, patterns of gene expression, metabolomics, urate, as well as protein profiling in the blood and CSF samples. Reduced brain regional N-acetyl-aspartate is a biomarker for the in vivo assessment of neuronal loss using magnetic resonance spectroscopy and T2 relaxation time with MRI. To confirm PD diagnosis, the PET biomarkers include [(18)F]-DOPA for estimating dopaminergic neurotransmission, [(18)F]dG for mitochondrial bioenergetics, [(18)F]BMS for mitochondrial complex-1, [(11)C](R)-PK11195 for microglial activation, SPECT imaging with (123)Iflupane and βCIT for dopamine transporter, and urinary salsolinol and 8-hydroxy, 2-deoxyguanosine for neuronal loss. This brief review describes the merits and limitations of recently discovered biomarkers and proposes coenzyme Q10, mitochondrial ubiquinone-NADH oxidoreductase, melatonin, α-synculein index, Charnoly body, and metallothioneins as novel biomarkers to confirm PD diagnosis for early and effective treatment of PD.

Identifying prodromal Parkinson's disease: pre-motor disorders in Parkinson's disease

Increasing recognition that Parkinson's disease (PD) may start outside of the substantia nigra has led to a rapidly expanding effort to define prodromal stages of PD, before motor signs permit classical diagnosis. Many of these efforts center around the identification of clinical non-motor symptoms and signs of disease. There is now direct evidence that olfaction, rapid eye movement (REM) sleep behavior disorder (RBD), constipation, and depression can be present in prodromal PD. In addition, there is suggestive evidence that visual changes, other autonomic symptoms, and subtle cognitive changes may also be present at prodromal stages. A critical issue in utility of these prodromal markers will be assessment of sensitivity, specificity, and positive and negative predictive values. Although these have yet to be fully defined, olfactory deficits, some visual changes, and autonomic symptoms occur in the majority of PD patients at diagnosis, suggesting good potential sensitivity. However, with the exception of RBD and perhaps some specific autonomic measures, specificity, and positive predictive value of these markers may be insufficient to be used alone as identifiers of prodromal disease. The evidence for the utility of olfaction, RBD, autonomic markers, visual changes, mood disorders, and cognitive loss as markers of prodromal PD and the potential sensitivity and specificity of these markers are summarized.

Neuroimaging: current role in detecting pre-motor Parkinson's disease

Convergent evidence suggests a pre-motor period in Parkinson's disease (PD) during which typical motor symptoms have not yet developed although dopaminergic neurons in the substantia nigra have started to degenerate. Advances in different neuroimaging techniques have allowed the detection of functional and structural changes in early PD. This review summarizes the state of the art knowledge concerning structural neuroimaging techniques including magnetic resonance imaging (MRI) and transcranial B-mode-Doppler-sonography (TCS) as well as functional neuroimaging techniques using radiotracer imaging (RTI) with different radioligands in detecting pre-motor PD.