Pathologic correlates of dementia in individuals with Lewy body disease

The potential roles of salivary biomarkers in neurodegenerative diseases

Current research efforts on neurodegenerative diseases are focused on identifying novel and reliable biomarkers for early diagnosis and insight into disease progression. Salivary analysis is gaining increasing interest as a promising source of biomarkers and matrices for measuring neurodegenerative diseases. Saliva collection offers multiple advantages over the currently detected biofluids as it is easily accessible, non-invasive, and repeatable, allowing early diagnosis and timely treatment of the diseases. Here, we review the existing findings on salivary biomarkers and address the potential value in diagnosing neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and Amyotrophic lateral sclerosis. Based on the available research, β-amyloid, tau protein, α-synuclein, DJ-1, Huntington protein in saliva profiles display reliability and validity as the biomarkers of neurodegenerative diseases.

Morphological differences between the two major subtypes of multiple system atrophy with cognitive impairment

OBJECTIVE

To compare the neuropathology between two types of multiple system atrophy - parkinsonism-predominant (MSA-P) and cerebellar ataxia-predominant (MSA-C) with cognitive impairment.

MATERIAL & METHODS

35 cases of MSA-P (mean age at death 60.5 ± 7.8 years) and 15 cases of MSA-C (mean age at death 61.3 ± 6.8 years), 35.% of which associated with mild to moderate cognitive impairment and one with severe dementia, were examined neuropathologically with semiquantitative evaluation of both α-synuclein and Alzheimer pathologies, including cerebral amyloid angiopathy (CAA) and other co-pathologies.

RESULTS

While the mean age at death of both MSA subgroups was similar, the age at onset and duration of disease were slightly higher in the MSA-C group. In line with the classification, the αSyn pathology glial and neuronal inclusions in both the cortex and brainstem were significantly higher in the MSA-P group. With regard to the Alzheimer disease pathology, tau load in cases with mild to moderate cognitive impairment was slightly but not significantly higher in the MSA-P group, one with severe dementia showing fully developed Alzheimer co-pathology, while the amyloid-β (Aβ) load including the CAA was higher in the MSA-C group. The presence of Lewy co-pathology in this series (20%), being similar to that of other MSA cohorts, was more frequent in MSA cases with mild to severe cognitive impairment, but did not differ between the two subgroups and seems not essentially important for MCI in MSA.

CONCLUSIONS

In agreement with previous clinical studies that reported more severe cognitive dysfunction in patients with MSA-P, the present neuropathological study showed increased tau pathology in MSA-P and one with severe Alzheimer co-pathology, but only slightly increased amyloid pathology in the MSA-C group. Lewy co-pathology was more frequent in MSA-P cases with cognitive decline. In view of the limited data about the pathobiological basis of cognitive impairment in MSA, further studies to elucidate the differences between the two phenotypes are urgently needed.

Morphological basis of Parkinson disease-associated cognitive impairment: an update

Cognitive impairment is one of the most salient non-motor symptoms of Parkinson disease (PD) that poses a significant burden on the patients and carers as well as being a risk factor for early mortality. People with PD show a wide spectrum of cognitive dysfunctions ranging from subjective cognitive decline and mild cognitive impairment (MCI) to frank dementia. The mean frequency of PD with MCI (PD-MCI) is 25.8% and the pooled dementia frequency is 26.3% increasing up to 83% 20 years after diagnosis. A better understanding of the underlying pathological processes will aid in directing disease-specific treatment. Modern neuroimaging studies revealed considerable changes in gray and white matter in PD patients with cognitive impairment, cortical atrophy, hypometabolism, dopamine/cholinergic or other neurotransmitter dysfunction and increased amyloid burden, but multiple mechanism are likely involved. Combined analysis of imaging and fluid markers is the most promising method for identifying PD-MCI and Parkinson disease dementia (PDD). Morphological substrates are a combination of Lewy- and Alzheimer-associated and other concomitant pathologies with aggregation of α-synuclein, amyloid, tau and other pathological proteins in cortical and subcortical regions causing destruction of essential neuronal networks. Significant pathological heterogeneity within PD-MCI reflects deficits in various cognitive domains. This review highlights the essential neuroimaging data and neuropathological changes in PD with cognitive impairment, the amount and topographical distribution of pathological protein aggregates and their pathophysiological relevance. Large-scale clinicopathological correlative studies are warranted to further elucidate the exact neuropathological correlates of cognitive impairment in PD and related synucleinopathies as a basis for early diagnosis and future disease-modifying therapies.

Salivary biomarkers of neurodegenerative and demyelinating diseases and biosensors for their detection

Salivary analysis is gaining increasing interest as a novel and promising field of research for the diagnosis of neurodegenerative and demyelinating diseases related to aging. The collection of saliva offers several advantages, being noninvasive, stress-free, and repeatable. Moreover, the detection of biomarkers directly in saliva could allow an early diagnosis of the disease, leading to timely treatments. The aim of this manuscript is to highlight the most relevant researchers' findings relatively to salivary biomarkers of neurodegenerative and demyelinating diseases, and to describe innovative and advanced biosensing strategies for the detection of salivary biomarkers. This review is focused on five relevant aging-related neurodegenerative disorders (Alzheimer's disease, Parkinson's disease, Amyotrophic Lateral Sclerosis, Huntington's disease, Multiple Sclerosis) and the salivary biomarkers most commonly associated with them. Advanced biosensors enabling molecular diagnostics for the detection of salivary biomarkers are presented, in order to stimulate future research in this direction and pave the way for their clinical application.

Application of Cerebrospinal Fluid AT(N) Framework on the Diagnosis of AD and Related Cognitive Disorders in Chinese Han Population

Background

Studies concerning the impact of the AT(N) framework on diagnostic capability in the dementia population are lacking. We aimed to explore the diagnostic application of CSF AT(N) framework in clinical routines of Alzheimer's disease (AD) as well as differential diagnosis of other cognitive diseases in the Chinese Han population.

Patients and Methods

A total of 137 patients with cognitive disorders received CSF tests of Aβ₄₂, t-tau and p-tau₁₈₁. Their CSF biomarker results were categorized and interpreted by the AT(N) framework. Neurologists provided a diagnosis both pre- and post-CSF biomarker disclosure with corresponding diagnostic confidence.

Results

The total initial diagnosis included 79 patients with AD and 58 patients with non-AD (NAD). The results of CSF biomarkers led to a diagnostic change of 28% in the cohort. Approximately 81.5% (n=53) of 65 patients whose CSF biomarker showed an underlying AD pathology were finally diagnosed as AD, with an increase of 17.5% in diagnostic confidence. Thirty-seven CSF results indicating NAD pathologic changes contributed to an exclusion of AD in 56.8% (n=21) of the patients along with a modest increase of 9.8% in average confidence. Thirty-five patients with normal CSF biomarkers maintained the diagnosis of NAD in 68.6% (n=24) of the group, leading to a slight elevation of 7.6% in confidence.

Conclusion

We found that the presence of amyloid pathology (A+) is contributable to diagnosing AD and improving confidence. On occasion of negative amyloid pathology (A-), with or without tau pathology, gaining uncertainty of the primary AD diagnosis would diminish the corresponding confidence. To the best of our knowledge, this is the first study performed in the Chinese Han population with cognitive disorders that explores the clinical capability of CSF AT(N) framework in a quantitative way.

Neuropathological findings in multiple system atrophy with cognitive impairment

Cognitive impairment (CI), previously considered an exclusion criterium for the diagnosis of multiple system atrophy (MSA) according to the second consensus criteria, is not uncommon in MSA. Mild cognitive impairment (MCI) has been reported in up to 47% of MSA patients, while severe dementia is rare. We related clinical CI with neuropathological findings in 48 autopsy-proven cases of MSA. This retrospective study included 33 parkinsonism predominant MSA (MSA-P), and 15 cerebellar ataxia-predominant MSA (MSA-C) cases (mean age at death 60.5 ± 7.8; range 46-82 years). Cognitive state was assessed from hospital charts, however, without comprehensive neuropsychological testing. Neuropathological examination, in addition to grading of the MSA pathologies, included semiquantitative assessment of Lewy and Alzheimer-related co-pathologies. Their incidence was compared with 143 age-matched controls (mean age 60.5 ± 7.6 years). MCI reported in ten cases (20.8%) was associated with moderate cortical tau pathology in only three; moderate CI in seven patients (14.5%) was associated with cortical amyloid plaques and moderate cortical tau pathology in six each, and one with probable primary age-related tauopathy (PART); a female aged 82 years with severe dementia showed fully developed Alzheimer disease. Cortical amyloid plaques, observed in eight cases, three of them without tau pathology, were associated with clinical MCI, as was cortical Lewy pathology in five. Two cases with cortical Lewy pathology and neuritic Braak stages II and III, and three with Braak stage IV, without cortical Lewy bodies, had shown moderate CI. Cortical Lewy pathology observed in four cases was not associated with clinical CI. 77.1% of the MSA cases were free of Alzheimer-type lesions, compared to 42% of controls; while Lewy pathology in the MSA cohort (22.9%) was significantly higher than in the control group (8.4%) both p < 0.001. Mild-to-moderate CI, reported in 35.3% of MSA patients, being significantly older than those without CI, were frequently associated with cortical Alzheimer (Braak stages III and IV) and Lewy pathologies, while only one with severe dementia had fully developed Alzheimer disease. In view of these findings in a limited series of MSA patients, further studies to elucidate the pathological basis of cognitive impairment in MSA are warranted.

Contribution of Alzheimer's disease neuropathologic change to the cognitive dysfunction in human brains with Lewy body-related pathology

This study investigated the clinicopathological relationship between cognitive dysfunction and Lewy body-related pathology (LRP), and the role of Alzheimer's disease neuropathologic change (ADNC) in affecting this relationship in the Chinese population. A total of 127 brains with antemortem cognition assessment were collected. The postmortem neuropathological classification of LRP and staging of ADNC were evaluated. Pairwise correlation and ordered logistic regression analysis showed that LRP had a moderate correlation with Global Everyday Cognition scores. The proportion of the people with intermediate and high levels of comorbid ADNC increased with the deterioration of LRP. The fit of the cognition prediction model improved when we incorporated both LRP and ADNC into the model compared with LRP alone. Our study indicated that comorbid ADNC can variably present in patients with Lewy body disease. A combination of LRP and concurrent ADNC improves the prediction of cognitive dysfunction compared with LRP alone. These findings may suggest the potential benefit of combined therapeutic approaches targeting concurrent pathological pathways for the Lewy body diseases in the Chinese population.

Progressive parkinsonism in older adults is related to the burden of mixed brain pathologies

OBJECTIVE

To examine whether indices of Parkinson disease (PD) pathology and other brain pathologies are associated with the progression of parkinsonism in older adults.

METHODS

We used data from decedents who had undergone annual clinical testing prior to death and structured brain autopsy. Parkinsonism was based on assessment with a modified Unified Parkinson's Disease Rating Scale and a clinical diagnosis of PD was based on medical history. We used a series of mixed-effects models controlling for age and sex to investigate the association of PD pathology (nigral neuronal loss and Lewy bodies) and indices of 8 other brain pathologies with the progression of parkinsonism prior to death.

RESULTS

During an average of 8.5 years' follow-up, more than half (771/1,430, 53.9%) developed parkinsonism proximate to death. On average, parkinsonism was progressive (estimate 0.130, SE 0.005, p < 0.001) in all older adults, but more rapid in adults with a clinical diagnosis of PD (n = 52; 3.6%) (estimate 0.066, SE 0.021, p < 0.001). Progression of parkinsonism was more rapid in adults with PD pathology (estimate 0.087, SE 0.013, p < 0.001). Alzheimer disease and several cerebrovascular pathologies were all independently associated with more rapid progression (all p values <0.05). The association between a higher person-specific weighted pathology score and more rapidly progressive parkinsonism did not differ between individuals with and without a clinical diagnosis of PD (estimate 0.003, SE 0.047, p = 0.957).

CONCLUSION

The rate of progressive parkinsonism in older adults with and without a clinical diagnosis of PD is related to the burden of mixed brain pathologies.

Spinal Lewy body pathology in older adults without an antemortem diagnosis of Parkinson's disease

To test the hypothesis that Lewy body pathology (LBs) is present in the spinal cord of older community-dwelling adults without a clinical diagnosis of Parkinson's disease (PD). We studied 162 prospective autopsies from older adults with PD (N = 6) and without PD (N = 156). We documented the presence of LBs in cerebrum and brainstem structures from each of the six regions used for Braak PD staging and four spinal cord levels (C5/6, T7, L4/5 and S4/5). Parkinsonism proximate to death was based on a previously validated measure present if two or more of the four signs of parkinsonism were present based on a modified version of the Unified Parkinson's Disease Rating Scale (UPDRS). Fifty-three of 156 individuals without PD (34%) had LBs in a least one site within the CNS. About half of cases with LBs in the cerebrum or brainstem, (25/53, 47%) also had spinal LBs. Almost 90% (22/25, 88%) of cases with spinal LBs had LBs in the cerebrum (Braak stages 4-6) and about 10% (3/25, 12%) had only brainstem LBs (Braak stages 1-3). Four of six cases with PD showed LBs in cerebrum, brainstem and spinal cord. Individuals with LBs in the spinal cord were more likely to have clinical parkinsonism proximate to death compared to individuals with LBs in brainstem and cerebrum alone (52% vs. 32%; Chi-Square x2  = 5.368, d.f. = 1, P = 0.0.021) and more severe nigral neuronal loss (48% vs. 11%; Chi-Square x2  = 9.049, d.f. = 1, P = 0.003). These findings were unchanged when we included cases with a history of PD. Older community-dwelling adults without a clinical diagnosis of PD have evidence of LBs throughout the CNS including the spinal cord which is associated with parkinsonism and more severe nigral neuronal loss.

Impact of the biological definition of Alzheimer's disease using amyloid, tau and neurodegeneration (ATN): what about the role of vascular changes, inflammation, Lewy body pathology?

BACKGROUND

The NIA-AA research framework proposes a biological definition of Alzheimer's disease, where asymptomatic persons with amyloid deposition would be considered as having this disease prior to symptoms.

DISCUSSION

Notwithstanding the fact that amyloid deposition in isolation is not associated with dementia, even the combined association of amyloid and tau pathology does not inevitably need to dementia over age 65. Other pathological factors may play a leading or an accelerating role in age-associated cognitive decline, including vascular small vessel disease, neuroinflammation and Lewy Body pathology.

CONCLUSION

Research should aim at understanding the interaction between all these factors, rather than focusing on them individually. Hopefully this will lead to a personalized approach to the prevention of brain aging, based on individual biological, genetic and cognitive profiles.

Cerebrospinal fluid α-synuclein contributes to the differential diagnosis of Alzheimer's disease

INTRODUCTION

The ability of Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarkers (amyloid β peptide 1-42, total tau, and phosphorylated tau) to discriminate AD from related disorders is limited. Biomarkers for other concomitant pathologies (e.g., CSF α-synuclein [α-syn] for Lewy body pathology) may be needed to further improve the differential diagnosis.

METHODS

CSF total α-syn, phosphorylated α-syn at Ser129, and AD CSF biomarkers were evaluated with Luminex immunoassays in 367 participants, followed by validation in 74 different neuropathologically confirmed cases.

RESULTS

CSF total α-syn, when combined with amyloid β peptide 1-42 and either total tau or phosphorylated tau, improved the differential diagnosis of AD versus frontotemporal dementia, Lewy body disorders, or other neurological disorders. The diagnostic accuracy of the combined models attained clinical relevance (area under curve ∼0.9) and was largely validated in neuropathologically confirmed cases.

DISCUSSION

Combining CSF biomarkers representing AD and Lewy body pathologies may have clinical value in the differential diagnosis of AD.

Neuropathology of Nonmotor Symptoms of Parkinson's Disease

Parkinson's disease (PD), a multiorgan neurodegenerative disorder associated with α-synuclein deposits throughout the nervous system and many organs, is clinically characterized by motor and nonmotor features, many of the latter antedating motor dysfunctions by 20 or more years. The causes of the nonmotor manifestations such as olfactory, autonomic, sensory, neuropsychiatric, visuospatial, sleep, and other disorders are unlikely to be related to single lesions. They are mediated by the involvement of both dopaminergic and nondopaminergic systems, and diverse structures outside the nigrostriatal system that is mainly responsible for the motor features of PD. The nonmotor alterations appear in early/prodromal stages of the disease and its further progression, suggesting a topographical and chronological spread of the lesions. This lends further support for the notion that PD is a multiorgan proteinopathy, although the exact relationship between presymptomatic and later developing nonmotor features of PD and neuropathology awaits further elucidation.

Alzheimer's disease neuropathologic change, Lewy body disease, and vascular brain injury in clinic- and community-based samples

We examined the relationships between Alzheimer's disease neuropathologic change (ADNC), Lewy body disease (LBD), and vascular brain injury (VBI) in 2 large autopsy samples. Because findings may differ between study populations, data came from U.S. Alzheimer's Disease Centers contributing to the National Alzheimer's Coordinating Center (n = 2742) and from the population-based Adult Changes in Thought study (n = 499). Regardless of study population, over 50% of participants with ADNC had co-occurring LBD or VBI; the majority of whom had a clinical AD dementia diagnosis prior to death. Overlap of pathologies was similar between studies, especially after standardizing to the distribution of age and dementia status in the Adult Changes in Thought population. LBD, but not VBI, was positively associated with ADNC in both studies. Interestingly, cortical LBD was more common in those with intermediate ADNC compared to low or high ADNC, especially in the National Alzheimer's Coordinating Center (p < 0.001). High prevalence of co-occurring neuropathologies among older adults with dementia has implications for accurate diagnosis of dementia etiologies and development of disease-modifying strategies.

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.

Neuropathologically mixed Alzheimer's and Lewy body disease: burden of pathological protein aggregates differs between clinical phenotypes

Multiple different pathological protein aggregates are frequently seen in human postmortem brains and hence mixed pathology is common. Mixed dementia on the other hand is less frequent and neuropathologically should only be diagnosed if criteria for more than one full blown disease are met. We quantitatively measured the amount of hyperphosphorylated microtubule associated tau (HP-τ), amyloid-β protein (Aβ) and α-synuclein (α-syn) in cases that were neuropathologically diagnosed as mixed Alzheimer's disease (AD) and neocortical Lewy body disease (LBD) but clinically presented either as dementia due to AD or LBD, the latter including dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). Our study group consisted of 28 cases (mean age, 76.11 SE: ±1.29 years; m:f, 17:11) of which 19 were neuropathologically diagnosed as mixed AD/DLB. Clinically, 8 mixed AD/DLB cases were diagnosed as AD (cAD), 8 as DLB (cDLB) and 3 as PDD (cPDD). In addition, we investigated cases that were both clinically and neuropathologically diagnosed as either AD (pure AD; n = 5) or DLB/neocortical LBD (pure DLB; n = 4). Sections from neocortical, limbic and subcortical areas were stained with antibodies against HP-τ, Aβ and α-syn. The area covered by immunopositivity was measured using image analysis. cAD cases had higher HP-τ loads than both cDLB and cPDD and the distribution of HP-τ in cAD was similar to the one observed in pure AD whilst cDLB showed comparatively less hippocampal HP-τ load. cPDD cases showed lower HP-τ and Aβ loads and higher α-syn loads. Here, we show that in neuropathologically mixed AD/DLB cases both the amount and the topographical distribution of pathological protein aggregates differed between distinct clinical phenotypes. Large-scale clinicopathological correlative studies using a quantitative methodology are warranted to further elucidate the neuropathological correlate of clinical symptoms in cases with mixed pathology.

Advanced age, cardiovascular risk burden, and timed up and go test performance in Parkinson disease

BACKGROUND

Cardiovascular comorbidities are a known risk factor for impaired mobility in elderly individuals. Motor impairments in Parkinson disease are conventionally ascribed to nigrostriatal dopaminergic denervation although progressive gait and balance impairments become more common with aging and often show limited response to dopaminergic replacement therapies.

METHODS

We explored the association between elevated cardiovascular risk factors and performance on the Timed Up and Go test in cross-sectional of Parkinson disease subjects (n = 83). Cardiovascular risk factor status was estimated using the Framingham General Cardiovascular Disease risk-scoring algorithm in order to dichotomize the cohort into those with and without elevated modifiable cardiovascular risk compared with normative scores for age and gender. All subjects underwent clinical and neuroimaging evaluations including a 3-m Timed Up and Go test, [(11)C]dihydrotetrabenazine positron emission tomography imaging to estimate nigrostriatal dopamine terminal loss, and an magnetic resonance imaging assessment of leukoaraiosis. A similar analysis was performed in 49 healthy controls.

RESULTS

After adjusting for disease duration, leukoaraiosis, and nigrostriatal dopaminergic denervation, Parkinson disease subjects with elevated Framingham risk scores (n = 61) displayed slower Timed Up and Go test performance (β = 1.86, t = 2.41, p = .018) compared with subjects with normal range Framingham risk scores (n = 22). When age ≥65 was added to the model in a post hoc analysis, the strength of effect seen with older age (β = 1.51, t = 2.44, p = .017) was similar to that of elevated Framingham risk scoring (β = 1.87, t = 2.51, p = .014). In a multivariable regression model studying the healthy control population, advanced age (t = 2.15, p = .037) was a significant predictor of Timed Up and Go speed though striatal [(11)C]dihydrotetrabenazine (t = -1.30, p = .19) and elevated Framingham risk scores (t = 1.32, p = .19) were not.

CONCLUSIONS

Modifiable cardiovascular risk factors and older age may independently exacerbate balance-related disability in Parkinson disease and may exert additive or synergistic pathological effects. The pathophysiology of these impairments cannot be explained completely by nigrostriatal dopaminergic denervation or leukoaraiosis burden and may relate to systemic factors seen with accelerated aging.

Building a pipeline to discover and validate novel therapeutic targets and lead compounds for Alzheimer's disease

Cognitive decline, Alzheimer's disease (AD) and other causes are major public health problems worldwide. With changing demographics, the number of persons with dementia will increase rapidly. The treatment and prevention of AD and other dementias, therefore, is an urgent unmet need. There have been considerable advances in understanding the biology of many age-related disorders that cause dementia. Gains in understanding AD have led to the development of ante-mortem biomarkers of traditional neuropathology and the conduct of several phase III interventions in the amyloid-β cascade early in the disease process. Many other intervention strategies are in various stages of development. However, efforts to date have met with limited success. A recent National Institute on Aging Research Summit led to a number of requests for applications. One was to establish multi-disciplinary teams of investigators who use systems biology approaches and stem cell technology to identify a new generation of AD targets. We were recently awarded one of three such grants to build a pipeline that integrates epidemiology, systems biology, and stem cell technology to discover and validate novel therapeutic targets and lead compounds for AD treatment and prevention. Here we describe the two cohorts that provide the data and biospecimens being exploited for our pipeline and describe the available unique datasets. Second, we present evidence in support of a chronic disease model of AD that informs our choice of phenotypes as the target outcome. Third, we provide an overview of our approach. Finally, we present the details of our planned drug discovery pipeline.

Association of Parkinson disease risk loci with mild parkinsonian signs in older persons

IMPORTANCE

Parkinsonian motor signs are common in the aging population and are associated with adverse health outcomes. Compared with Parkinson disease (PD), potential genetic risk factors for mild parkinsonian signs have been largely unexplored.

OBJECTIVE

To determine whether PD susceptibility loci are associated with parkinsonism or substantia nigra pathology in a large community-based cohort of older persons.

DESIGN, SETTING, AND PARTICIPANTS

Eighteen candidate single-nucleotide polymorphisms from PD genome-wide association studies were evaluated in a joint clinicopathologic cohort. Participants included 1698 individuals and a nested autopsy collection of 821 brains from the Religious Orders Study and the Rush Memory and Aging Project, 2 prospective community-based studies.

MAIN OUTCOMES AND MEASURES

The primary outcomes were a quantitative measure of global parkinsonism or component measures of bradykinesia, rigidity, tremor, and gait impairment that were based on the motor Unified Parkinson's Disease Rating Scale. In secondary analyses, we examined associations with additional quantitative motor traits and postmortem indices, including substantia nigra Lewy bodies and neuronal loss.

RESULTS

Parkinson disease risk alleles in the MAPT (rs2942168; P = .0006) and CCDC62 (rs12817488; P = .004) loci were associated with global parkinsonism, and these associations remained after exclusion of patients with a PD diagnosis. Based on motor Unified Parkinson's Disease Rating Scale subscores, MAPT (P = .0002) and CCDC62 (P = .003) were predominantly associated with bradykinesia, and we further discovered associations between SREBF1 (rs11868035; P = .005) and gait impairment, SNCA (rs356220; P = .04) and rigidity, and GAK (rs1564282; P = .03) and tremor. In the autopsy cohort, only NMD3 (rs34016896; P = .03) was related to nigral neuronal loss, and no associations were detected with Lewy bodies.

CONCLUSIONS AND RELEVANCE

In addition to the established link to PD susceptibility, our results support a broader role for several loci in the development of parkinsonian motor signs and nigral pathology in older persons.

Dysfunction of the locus coeruleus-norepinephrine system and related circuitry in Parkinson's disease-related dementia

Although resting tremor, cogwheel rigidity, hypokinesia/bradykinesia and postural instability usually dominate the clinical picture of sporadic Parkinson's disease (PD), both clinical and epidemiological data reveal that a wide variety of additional symptoms impair patients' quality of life considerably, parallel to the chronic progressive neurodegenerative movement disorder. Autopsy based retrospective studies have shown that α-synuclein immunoreactive Lewy pathology (LP) develops in the locus coeruleus (LC) of patients with neuropathologically confirmed sporadic PD, as well as in individuals with incidental (prodromal or premotor) Lewy body disease but not in age and gender matched controls. Using five case studies, this review discusses the possible role of LP (axonopathy, cellular dysfunction and nerve cell loss) in the LC, catecholaminergic tract and related circuitry in the development of PD-related dementia. The contribution of noradrenergic deficit to cognitive dysfunction in PD has been underappreciated. Noradrenergic therapeutic interventions might not only alleviate depressive symptoms and anxiety but also delay the onset of cognitive decline.

Neuropathology of sporadic Parkinson's disease: evaluation and changes of concepts

Parkinson's disease (PD), one of the most frequent neurodegenerative disorders, is no longer considered a complex motor disorder characterized by extrapyramidal symptoms, but a progressive multisystem or-more correctly-multiorgan disease with variegated neurological and nonmotor deficiencies. It is morphologically featured not only by the degeneration of the dopaminergic nigrostriatal system, responsible for the core motor deficits, but by multifocal involvement of the central, peripheral and autonomic nervous system and other organs associated with widespread occurrence of Lewy bodies and dystrophic Lewy neurites. This results from deposition of abnormal α-synuclein (αSyn), the major protein marker of PD, and other synucleinopathies. Recent research has improved both the clinical and neuropathological diagnostic criteria of PD; it has further provided insights into the development and staging of αSyn and Lewy pathologies and has been useful in understanding the pathogenesis of PD. However, many challenges remain, for example, the role of Lewy bodies and the neurobiology of axons in the course of neurodegeneration, the relation between αSyn, Lewy pathology, and clinical deficits, as well as the interaction between αSyn and other pathologic proteins. Although genetic and experimental models have contributed to exploring the causes, pathomechanisms, and treatment options of PD, there is still a lack of an optimal animal model, and the etiology of this devastating disease is far from being elucidated.

Diet and Alzheimer's disease risk factors or prevention: the current evidence

Preventing or postponing the onset of Alzheimer's disease (AD) and delaying or slowing its progression would lead to a consequent improvement of health status and quality of life in older age. Elevated saturated fatty acids could have negative effects on age-related cognitive decline and mild cognitive impairment (MCI). Furthermore, at present, epidemiological evidence suggests a possible association between fish consumption, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA; in particular, n-3 PUFA) and a reduced risk of cognitive decline and dementia. Poorer cognitive function and an increased risk of vascular dementia (VaD) were found to be associated with a lower consumption of milk or dairy products. However, the consumption of whole-fat dairy products may be associated with cognitive decline in the elderly. Light-to-moderate alcohol use may be associated with a reduced risk of incident dementia and AD, while for VaD, cognitive decline and predementia syndromes, the current evidence is only suggestive of a protective effect. The limited epidemiological evidence available on fruit and vegetable consumption and cognition generally supports a protective role of these macronutrients against cognitive decline, dementia and AD. Only recently, higher adherence to a Mediterranean-type diet was associated with decreased cognitive decline, although the Mediterranean diet (MeDi) combines several foods, micro- and macro-nutrients already separately proposed as potential protective factors against dementia and predementia syndromes. In fact, recent prospective studies provided evidence that higher adherence to a Mediterranean-type diet could be associated with slower cognitive decline, reduced risk of progression from MCI to AD, reduced risk of AD and a decreased all-cause mortality in AD patients. These findings suggested that adherence to the MeDi may affect not only the risk of AD, but also of predementia syndromes and their progression to overt dementia. Based on the current evidence concerning these factors, no definitive dietary recommendations are possible. However, following dietary advice for lowering the risk of cardiovascular and metabolic disorders, high levels of consumption of fats from fish, vegetable oils, nonstarchy vegetables, low glycemic index fruits and a diet low in foods with added sugars and with moderate wine intake should be encouraged. Hopefully this will open new opportunities for the prevention and management of dementia and AD.

Synuclein deposition and non-motor symptoms in Parkinson disease

Parkinson disease (PD) is a multisystem neurodegenerative disorder clinically characterized by motor and non-motor (NM) symptoms. The causes of NM symptoms in PD, many of which antedating motor dysfunction, are multifocal and unlikely explained by single lesions. They include olfactory, autonomic, sensory, skin, sleep, visual, neuropsychiatric, and other manifestations. Most NM features in PD are related to α-synuclein pathology which, in addition to the dopaminergic striatonigral system, involves non-nigral brainstem nuclei, sympathetic, parasympathetic, enteric and pelvic plexuses, cardiac systems, submandibular gland, adrenal medulla, skin, retina, and other visceral organs. This suggests a topographical and chronological spread of lesions, particularly in the prodromal stages of the disease, which, however, awaits further confirmation. A few animal models are available that recapitulate NM symptoms in human PD, but their validity is under discussion. More studies are warranted to refine the exact correlations between presymptomatic and late-developing NM features of PD and α-synuclein pathology as a basis for more effective preventive and therapeutic options of this devastating disease.

Assessment of mild dementia with amyloid and dopamine terminal positron emission tomography

We assessed the relationship between consensus clinical diagnostic classification and neurochemical positron emission tomography imaging of striatal vesicular monoamine transporters and cerebrocortical deposition of aβ-amyloid in mild dementia. Seventy-five subjects with mild dementia (Mini-Mental State Examination score≥18) underwent a conventional clinical evaluation followed by 11C-dihydrotetrabenazine positron emission tomography imaging of striatal vesicular monoamine transporters and 11C-Pittsburgh compound-B positron emission tomography imaging of cerebrocortical aβ-amyloid deposition. Clinical classifications were assigned by consensus of an experienced clinician panel. Neuroimaging classifications were assigned as Alzheimer's disease, frontotemporal dementia or dementia with Lewy bodies on the basis of the combined 11C-dihydrotetrabenazine and 11C-Pittsburgh compound-B results. Thirty-six subjects were classified clinically as having Alzheimer's disease, 25 as having frontotemporal dementia and 14 as having dementia with Lewy bodies. Forty-seven subjects were classified by positron emission tomography neuroimaging as having Alzheimer's disease, 15 as having dementia with Lewy bodies and 13 as having frontotemporal dementia. There was only moderate agreement between clinical consensus and neuroimaging classifications across all dementia subtypes, with discordant classifications in ∼35% of subjects (Cohen's κ=0.39). Discordant classifications were least frequent in clinical consensus Alzheimer's disease (17%), followed by dementia with Lewy bodies (29%) and were most common in frontotemporal dementia (64%). Accurate clinical classification of mild neurodegenerative dementia is challenging. Though additional post-mortem correlations are required, positron emission tomography imaging likely distinguishes subgroups corresponding to neurochemically defined pathologies. Use of these positron emission tomography imaging methods may augment clinical classifications and allow selection of more uniform subject groups in disease-modifying therapeutic trials and other prospective research involving subjects in the early stages of dementia.

Cerebrospinal fluid biomarkers and cognitive performance in non-demented patients with Parkinson's disease

We tested the hypothesis that levels of CSF biomarkers associated with dementia and cognitive impairment are correlated with cognitive performance in non-demented Parkinson's disease (PD) patients. Twenty-two non-demented patients with PD underwent neuropsychological testing and lumbar puncture to collect CSF. We correlated performance scores on the Logical Memory (delayed), Category Fluency, Digit Symbol, and Trails B minus A with CSF concentrations of amyloid (A) β(42), total tau (t-tau), Aβ(42)/t-tau, and Brain Derived Neurotrophic Factor (BDNF). We observed significant associations between performance on the Digit Symbol test and CSF levels of Aβ(42), Aβ(42)/t-tau, and BDNF, and between performance on the Category Fluency (vegetable) and Aβ(42)/t-tau. While several of these associations were attenuated by adjusting for age, our results suggest that it may be possible to use CSF biomarkers to characterize pathophysiologic processes underlying even mild cognitive deficits in non-demented PD patients.

Interaction between α-synuclein and tau in Parkinson's disease comment on Wills et al.: elevated tauopathy and α-synuclein pathology in postmortem Parkinson's disease brains with and without dementia. Exp Neurol 2010; 225: 210-218

Recent neurochemical studies in postmortem brains of patients with Parkinson's disease (PD), PD with dementia (PDD) and age-matched controls revealed significant decrease of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in striatum, confirming previous studies indicating substantial loss of dopaminergic neurons and terminals. Insoluble α-synuclein (αSyn) was significantly increased in both striata and inferior frontal gyrus (IFG), more severe in PDD, probably related to Lewy body (LB) burden discussed as one cause of dementia in PD. Parkin levels frequently related to recessive and young-onset PD were unchanged, suggesting no link to sporadic PD. Novel and most interesting data showed elevated tauopathy in striata of both PD and PDD, associated with increased levels of phosphorylated GSK-3β and reduced 20S proteasomal subunits but - despite increased cortical αSyn - unchanged pTau in IFG, related to increased pGSK-3β and decreased 19S proteasome subunits. These data, recently confirmed in PDGF-αSyn transgenic mice (Haggerty et al., submitted) suggest tauopathy in PD and PDD restricted to the dopaminergic nigrostriatal system and in various animal models of PD show topographic differences from a global tauopathy in Alzheimer's disease (AD) (and other tauopathies). Although some of these data are at variance to current neuropathologic findings in PD and PDD, they confirm frequently discussed correlations/overlaps between AD and PD/PDD and synergistic effects of αSyn, pTau, β-amyloid, and other pathologic proteins, suggesting a dualism or triad of neurodegeneration, the basic molecular pathogenesis remains to be elucidated.