Amyloid beta-peptide and the dementia of Parkinson's disease

Amyloid-beta and tau protein beyond Alzheimer's disease

ABSTRACT

The aggregation of amyloid-beta peptide and tau protein dysregulation are implicated to play key roles in Alzheimer's disease pathogenesis and are considered the main pathological hallmarks of this devastating disease. Physiologically, these two proteins are produced and expressed within the normal human body. However, under pathological conditions, abnormal expression, post-translational modifications, conformational changes, and truncation can make these proteins prone to aggregation, triggering specific disease-related cascades. Recent studies have indicated associations between aberrant behavior of amyloid-beta and tau proteins and various neurological diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as retinal neurodegenerative diseases like Glaucoma and age-related macular degeneration. Additionally, these proteins have been linked to cardiovascular disease, cancer, traumatic brain injury, and diabetes, which are all leading causes of morbidity and mortality. In this comprehensive review, we provide an overview of the connections between amyloid-beta and tau proteins and a spectrum of disorders.

Collusion of α-Synuclein and Aβ aggravating co-morbidities in a novel prion-type mouse model

BACKGROUND

The misfolding of host-encoded proteins into pathological prion conformations is a defining characteristic of many neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and Lewy body dementia. A current area of intense study is the way in which the pathological deposition of these proteins might influence each other, as various combinations of co-pathology between prion-capable proteins are associated with exacerbation of disease. A spectrum of pathological, genetic and biochemical evidence provides credence to the notion that amyloid β (Aβ) accumulation can induce and promote α-synuclein pathology, driving neurodegeneration.

METHODS

To assess the interplay between α-synuclein and Aβ on protein aggregation kinetics, we crossed mice expressing human α-synuclein (M20) with APPswe/PS1dE9 transgenic mice (L85) to generate M20/L85 mice. We then injected α-synuclein preformed fibrils (PFFs) unilaterally into the hippocampus of 6-month-old mice, harvesting 2 or 4 months later.

RESULTS

Immunohistochemical analysis of M20/L85 mice revealed that pre-existing Aβ plaques exacerbate the spread and deposition of induced α-synuclein pathology. This process was associated with increased neuroinflammation. Unexpectedly, the injection of α-synuclein PFFs in L85 mice enhanced the deposition of Aβ; whereas the level of Aβ deposition in M20/L85 bigenic mice, injected with α-synuclein PFFs, did not differ from that of mice injected with PBS.

CONCLUSIONS

These studies reveal novel and unexpected interplays between α-synuclein pathology, Aβ and neuroinflammation in mice that recapitulate the pathology of Alzheimer's disease and Lewy body dementia.

Neuropathological and Biomarker Findings in Parkinson's Disease and Alzheimer's Disease: From Protein Aggregates to Synaptic Dysfunction

There is mounting evidence that Parkinson’s disease (PD) and Alzheimer’s disease (AD) share neuropathological hallmarks, while similar types of biomarkers are being applied to both. In this review we aimed to explore similarities and differences between PD and AD at both the neuropathology and the biomarker levels, specifically focusing on protein aggregates and synapse dysfunction. Thus, amyloid-β peptide (Aβ) and tau lesions of the Alzheimer-type are common in PD and α-synuclein Lewy-type aggregates are frequent findings in AD. Modern neuropathological techniques adding to routine immunohistochemistry might take further our knowledge of these diseases beyond protein aggregates and down to their presynaptic and postsynaptic terminals, with potential mechanistic and even future therapeutic implications. Translation of neuropathological discoveries to the clinic remains challenging. Cerebrospinal fluid (CSF) and positron emission tomography (PET) markers of Aβ and tau have been shown to be reliable for AD diagnosis. Conversely, CSF markers of α-synuclein have not been that consistent. In terms of PET markers, there is no PET probe available for α-synuclein yet, while the AD PET markers range from consistent evidence of their specificity (amyloid imaging) to greater uncertainty of their reliability due to off-target binding (tau imaging). CSF synaptic markers are attractive, still needing more evidence, which currently suggests those might be non-specific markers of disease progression. It can be summarized that there is neuropathological evidence that protein aggregates of AD and PD are present both at the soma and the synapse. Thus, a number of CSF and PET biomarkers beyond α-synuclein, tau and Aβ might capture these different faces of protein-related neurodegeneration. It remains to be seen what the longitudinal outcomes and the potential value as surrogate markers of these biomarkers are.

On the Role of Platelet-Generated Amyloid Beta Peptides in Certain Amyloidosis Health Complications

As do many other immunity-related blood cells, platelets release antimicrobial peptides that kill bacteria, fungi, and even certain viruses. Here we review the literature suggesting that there is a similarity between the antimicrobials released by other blood cells and the amyloid-related Aβ peptide released by platelets. Analyzing the literature, we also propose that platelet-generated Aβ amyloidosis may be more common than currently recognized. This systemic Aβ from a platelet source may participate in various forms of amyloidosis in pathologies ranging from brain cancer, glaucoma, skin Aβ accumulation, and preeclampsia to Alzheimer’s disease and late-stage Parkinson’s disease. We also discuss the advantages and disadvantages of specific animal models for studying platelet-related Aβ. This field is undergoing rapid change, as it evaluates competing ideas in the light of new experimental observations. We summarized both in order to clarify the role of platelet-generated Aβ peptides in amyloidosis-related health disorders, which may be helpful to researchers interested in this growing area of investigation.

Association of rare variants in neurodegenerative genes with familial Alzheimer's disease

Objective

To investigate the impact of rare variants underlying neurodegenerative‐related genes to familial Alzheimer’s disease (AD).

Methods

We performed targeted sequencing of 277 neurodegenerative‐related genes on probands from 75 Chinese AD families non‐carrying causative mutation of dementia genes. Rare coding variants segregated in families were tested for association in an independent cohort of 506 patients with sporadic AD and 498 cognitively normal controls. East Asians data from the Exome Aggregation Consortium (ExAC) were used as a reference control.

Results

A novel rare variant, P410S of PLD3 was found in an early‐onset AD family. LRRK2 I2012T, a causative mutation of Parkinson’s disease, was identified in another early‐onset AD family. Missense variants in ABCA7 (P143S and A1507T) and CR1(T239M) were significantly associated with familial AD (P = 0.005437, 0.001383, 0.000549), a missense variant in TREM2(S183C) was significantly associated with AD (P = 0.000396) when compared with the East Asian controls in ExAC database. A non‐frameshift variant in FUS (G223del) was frequent in AD cases and significantly associated with familial AD (P = 0.008).

Interpretation

Multiple rare coding variants of causal and risk neurodegenerative genes were presented in clinically diagnosed AD families that may confer risk of AD. Our data supported that the clinical, pathological, and genetic architectures of AD, PD, and FTD/ALS may overlapping. We propose that targeted sequencing on neurodegenerative‐related genes is necessary for genetically unclear AD families.

Neuropathology of dementia in patients with Parkinson's disease: a systematic review of autopsy studies

BACKGROUND

Dementia is a common, debilitating feature of late Parkinson's disease (PD). PD dementia (PDD) is associated with α-synuclein propagation, but coexistent Alzheimer's disease (AD) pathology may coexist. Other pathologies (cerebrovascular, transactive response DNA-binding protein 43 (TDP-43)) may also influence cognition. We aimed to describe the neuropathology underlying dementia in PD.

METHODS

Systematic review of autopsy studies published in English involving PD cases with dementia. Comparison groups included PD without dementia, AD, dementia with Lewy bodies (DLB) and healthy controls.

RESULTS

44 reports involving 2002 cases, 57.2% with dementia, met inclusion criteria. While limbic and neocortical α-synuclein pathology had the strongest association with dementia, between a fifth and a third of all PD cases in the largest studies had comorbid AD. In PD cases with dementia, tau pathology was moderate or severe in around a third, and amyloid-β pathology was moderate or severe in over half. Amyloid-β was associated with a more rapid cognitive decline and earlier mortality, and in the striatum, distinguished PDD from DLB. Positive correlations between multiple measures of α-synuclein, tau and amyloid-β were found. Cerebrovascular and TDP-43 pathologies did not generally contribute to dementia in PD. TDP-43 and amyloid angiopathy correlated with coexistent Alzheimer pathology.

CONCLUSIONS

While significant α-synuclein pathology is the main substrate of dementia in PD, coexistent pathologies are common. In particular, tau and amyloid-β pathologies independently contribute to the development and pattern of cognitive decline in PD. Their presence should be assessed in future clinical trials where dementia is a key outcome measure.

TRIAL REGISTRATION NUMBER

CRD42018088691.

The impact of β-amyloid positron emission tomography on the diagnostic and treatment decisions of dementia experts

Aim: Amyloid positron emission tomography (aPET) measurement of Alzheimer's disease (AD) pathology could improve the accurate diagnosis of cognitive disorders. Appropriate use criteria recommend that only dementia experts order aPET. Materials & methods: We surveyed 145 dementia experts about their current approaches to evaluation and treatment and the likely influence of aPET. Results: Experts expected aPET to alter diagnostic procedures and patient management and also increase diagnostic certainty. They anticipated confirming AD or altering pharmacological treatment following positive results more than excluding AD following negative results. Experts familiar with aPET reported changes that were more consistent with appropriate use criteria and published evidence. Conclusions: Knowledge about aPET strongly influenced effects on diagnostic certainty and changed clinical practice. Dementia experts may need additional training to achieve optimal benefit from aPET.

The human cytomegalovirus non-coding Beta2.7 RNA as a novel therapeutic for Parkinson's disease--Translational research with no translation

Human cytomegalovirus (HCMV) encodes abundant numbers of microRNAs (miRNAs) and other non-coding RNAs (ncRNAs) whose functions are presently under intense investigation. In this chapter, we discuss the function of one of the more well characterised virus-encoded ncRNAs, derived from the viral major early gene (Beta2.7). This RNA plays an anti-apoptotic role during infection by directly interacting with mitochondrial complex I to help maintain high levels of ATP production and by preventing the stress induced re-localisation of retinoid/interferon-induced mortality-19 protein, GRIM-19. We then go on to describe how an 800 nucleotide sub-domain of the Beta2.7 transcript, p137, has been exploited in the development of a novel therapeutic for the treatment of Parkinson's disease.

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.

Imaging cognitive and behavioral symptoms in Parkinson's disease

Non-motor symptoms are a major and often unrecognized cause of morbidity of Parkinson's disease. In the past few years, imaging technology, such as functional MRI and PET, have provided a large bulk of information about the phenomena. Here, we provide an overview of those imaging studies that may help us understand the neuronal correlates associated with non-motor symptoms in Parkinson's disease, with a particular focus on cognitive and neuropsychiatric deficits.

Imaging amyloid in Parkinson's disease dementia and dementia with Lewy bodies with positron emission tomography

Although Parkinson's disease with later dementia (PDD) and dementia with Lewy bodies (DLB) are pathologically characterized by the presence of intraneuronal Lewy inclusion bodies, amyloid deposition is also associated to varying degrees with both these disorders. Fibrillar amyloid load can now be quantitated in vivo with positron emission tomography (PET) using imaging biomarkers. Here the reported findings of 11C-PIB PET studies concerning the amyloid load associated with PD and its influence on dementia are reviewed. It is concluded that the presence of amyloid acts to accelerate the dementia process in Lewy body disorders, though has little influence on its nature. Anti-amyloid strategies could be a relevant approach for slowing dementia in a number of DLB and PDD cases.

The morbid anatomy of dementia in Parkinson's disease

Dementia in Parkinson's disease (PD/PDD) is a common complication with a prevalence of up to 50%, but the specific changes underlying the cognitive decline remain undefined. Neuronal degeneration resulting in the dysfunction of multiple subcortical neurochemical projection systems has been described along with Lewy body-type pathology in cortical and limbic regions. Advanced alpha-synuclein (alphaSyn) pathology is not necessarily sufficient for producing dementia and concomitant Alzheimer's disease (AD) change has also been proposed as a possible substrate of PDD. A lack of consensus in the extant literature likely stems from clinical heterogeneity and variable reliability in clinical characterisation as well as other historical and methodological issues. The concurrent presence of abnormally deposited alphaSyn, amyloid-beta and tau proteins in the PDD brain and the interaction of these molecules in a linked pathological cascade of AD and PD-related mechanisms may prove important in determining the underlying pathological process for the development of dementia in PD and this concept of combined pathologies awaits further investigation.

Reduction of SorLA/LR11, a sorting protein limiting beta-amyloid production, in Alzheimer disease cerebrospinal fluid

BACKGROUND

The sortilin-related receptor SorLA/LR11 (LR11) is a transmembrane neuronal sorting protein that reduces beta-amyloid precursor protein trafficking to secretases, notably BACE1 that generates beta-amyloid, the principal component of senile plaques in Alzheimer disease (AD). LR11 protein is reduced in patients with late-onset AD, and LR11 polymorphisms have been associated with late-onset AD.

OBJECTIVE

T o detect soluble LR11 and APP in cerebrospinal fluid (CSF) from patients with AD and control subjects, as (like beta-amyloid precursor protein) LR11 is cleaved near the membrane to release a large N-terminal fragment that is secreted to media from cultured cells.

DESIGN

Case-control study.

SETTING

Academic research.

PARTICIPANTS

Patients with AD and control subjects.

MAIN OUTCOME MEASURES

We evaluated CSF LR11, beta-amyloid precursor protein, and apolipoprotein E levels by Western blot in lumbar and postmortem CSF samples.

RESULTS

LR11 levels were detectable and stable during 6 months in the CSF of patients with AD. LR11 levels were significantly reduced in lumbar samples from patients with mild to moderate probable AD, as well as in ventricular CSF from patients with autopsy-confirmed AD (predominantly Braak stage III-IV). Bivariate analysis with beta-amyloid 42 and LR11 levels improved diagnostic specificity for AD. Reduced LR11 levels are significantly correlated with soluble beta-amyloid precursor protein but not apolipoprotein E levels.

CONCLUSION

Reduced LR11 levels in CSF of patients with AD may have potential as a diagnostic biomarker for patients with LR11 deficits that promote beta-amyloid production or as an index of therapeutic response in late-onset AD.

Expression QTL and regulatory network analysis of microtubule-associated protein tau gene

Numerous studies have shown that the microtubule-associated protein tau (Mapt) gene plays an important role in tauopathies. However, little is known about the genetic regulatory network. In this study, we combined array analysis and quantitative trait loci (QTL) mapping approaches (genetical genomics) to characterize the expression variation and the regulatory network of Mapt in mouse. Through examining the probe sets for overlapping single nucleotide polymorphysms (SNPs), two probe sets without overlapping SNPs were selected for QTL mapping. Interval mapping results showed that expression quantitative trait loci (eQTL) mapping for Mapt had a significant linkage score (LRS) of 27.2. Moreover, the QTL was mapped to within 3 Mb of the location of the gene itself (Mapt) as a cis-acting QTL. Through mapping the joint modulation of Mapt, we identified 22 transcripts/genes with trans-regulated QTLs close to the location of Mapt. By further excluding the correlated transcripts due to linkage disequilibrium, the result highlighted three genes as potential downstream genes of Mapt. Expression correlation and genetic network analysis demonstrated that Mapt co-varies with many tauopathies-related genes, including Gsk3b, Falz, Apbb2, Slc1a3, Ntrk2, Pik3ca, and Ikbkap. These results demonstrate that the genetical genomics approach provides a powerful tool for constructing pathways that contribute to complex traits, such as neurodegenerative disorders.

Prevalence and impact of vascular and Alzheimer pathologies in Lewy body disease

Whereas the prevalence and impact of vascular pathology in Alzheimer diease (AD) are well established, the role of vascular and Alzheimer pathologies in the progression of neurodegeneration and cognitive impairment in Parkinson disease (PD) is under discussion. A retrospective clinico-pathologic study of 100 patients with autopsy proven PD (including 44 cases with dementia/PDD) and 20 cases of dementia with Lewy bodies (DLB) confirmed essential clinical (duration of illness, Mini-Mental State Examination/MMSE, age at death) and morphologic differences between these groups; Lewy body Braak scores and Alzheimer pathologies (neuritic Braak stage, cortical Abeta plaque load, and generalized cerebral amyloid angiopathy or CAA) were significantly higher/more severe in DLB and PDD than in PD without dementia. Duration of illness showed no association to any of the examined pathologic parameters, while there was a moderate association between LB scores and neuritic Braak stages, the latter significantly increasing with age. Significant association between cerebrovascular lesions and neuritic Braak stage was seen in PDD but not in PD subjects without dementia. These data suggest an influence of Alzheimer-related lesions on the progression of the neurodegenerative process and, in particular, on cognitive decline in both PDD and DLB. On the other hand, both these factors in PD and DLB appear to be largely independent from coexistent vascular pathology, except in cases with severe cerebrovascular lesions or those related to neuritic AD pathology. Assessment of ApoE genotype in a small number of cases showed no significant differences in the severity of Abeta plaque load and CAA except for much lower intensities in non-demented epsilon3/3 patients. Despite increasing evidence suggesting synergistic reactions between alpha-synuclein (alphaSyn), tau and Abeta-peptides, the major protein markers of both AD and Lewy body diseases, and of both vascular pathology and AD, the molecular background and pathophysiological impact of these pathologies on the progression of neurodegeneration and development of cognitive decline in PD await further elucidation.

Cerebral amyloid angiopathy in Lewy body disease

While Alzheimer and Lewy body pathologies are discussed as major substrates of dementia in Parkinson's disease (PD/Lewy body disease of brainstem type), the incidence and impact of cerebral amyloid angiopathy (CAA) and its association with cognitive decline in PD and dementia with Lewy bodies (DLB) are unknown. The severity of CAA and other Alzheimer lesions were assessed in 68 cases of autopsy-confirmed PD, 32 of them with dementia (PDD), and in 20 cases of DLB. PDD patients were significantly older than those without dementia (mean age 84.5 vs 77.6 years; p < 0.01), the age of DLB patients was in between both groups (mean 80.0 years), while duration of disease was DLB < PDD < PD (mean 6.5 vs 8.5 and 14.3 years). PDD patients had a significantly higher neuritic Braak stage (mean 4.2 vs 2.4, p < 0.01), significantly higher cortical amyloid beta (Abeta) load, capillary cerebral amyloid angiopathy (CapCAA) and generalized CAA than those without dementia (mild CapCAA in 22% vs moderate to severe CapCAA in 87%; mild generalized CAA in 5.5% vs moderate to severe generalized CAA in 82%). Mean PD stage was higher in both DLB and PDD than in PD (mean 5.2 vs 4.5 and 4.0, respectively): Mean neuritic Braak stage in DLB was 3.4, severe Abeta plaque load was seen in 95%, moderate to severe CapCAA in 90% and mild to severe generalized CAA in 70%. This and other recent studies imply an association of CAA with cognitive decline in both PD/PDD and DLB, particularly in cases with concomitant AD-type pathology.

Tauopathies and synucleinopathies: Do cerebrospinal fluid β-amyloid peptides reflect disease-specific pathogenesis?

To evaluate variations in amyloid beta (Abeta) peptide pattern in cerebrospinal fluid (CSF) in neurodegenerative disorders. A recently established quantitative urea-based Abeta-sodium-dodecylsulfate-polyacrylamide-gel-electrophoresis with western immunoblot (Abeta-SDS-PAGE/immunoblot) revealed a highly conserved Abeta peptide (Abeta1-37, 1-38, 1-39, 1-40, 1-42) pattern in CSF. We asked whether the variation might be useful to further elucidate the overlap between or distinctions among neurodegenerative diseases in Abeta-processing. We used the Abeta-SDS-PAGE/immunoblot to investigate CSF for disease-specific Abeta peptide patterns. CSF samples from 96 patients with mainly clinically diagnosed Alzheimer's disease (n = 15), progressive supranuclear palsy (n = 20), corticobasal degeneration (n = 12), Parkinson's disease (n = 11), multiple systems atrophy (n = 18), and dementia with Lewy-bodies (n = 20) were analysed as well a comparison group (n = 19). The Abeta peptide patterns varied between tauopathies and synucleinopathies and between all diseases and the comparison group, possibly due to the influence of tau and alpha-synuclein on Abeta-processing.

Heterogeneous factors in dementia with Parkinson's disease: IMP-SPECT study

BACKGROUND

Nature of the dementing process in Parkinson's disease, and particularly its relationship with Alzheimer's disease, diffuse Lewy body disease or frontal dementia remains controversial.

OBJECTIVE

We hypothesize that origins of dementia in Parkinson's disease are heterogeneous, so we compared cortical regional cerebral blood flow (rCBF) between Parkinson's disease patients with and without dementia.

PATIENTS

Forty consecutive patients with Hoehn-Yahr stage III or IV Parkinson's disease were used (13 patients had dementia (PDD group), and 27 patients had no dementia (PDND group)).

RESULTS

There were significant rCBF reductions in the left parietal association cortex and left frontal association cortex in PDD. Multiple logistic regression analysis demonstrated that only rCBF of the left frontal association cortex was significant. PDD patients were divided into three groups according to rCBF patterns: frontal hypoperfusion group, Alzheimer's disease-like group, and diffuse Lewy body disease-like group.

CONCLUSIONS

Controversial study results involving PDD patients may be mainly due to heterogeneity in dementing processes in Parkinson's disease.

CSF amyloid-beta-peptides in Alzheimer's disease, dementia with Lewy bodies and Parkinson's disease dementia

As the differential diagnosis of dementias based on established clinical criteria is often difficult, biomarkers for applicable diagnostic testing are currently under intensive investigation. Amyloid plaques deposited in the brain of patients suffering from Alzheimer's disease, dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) mainly consist of carboxy-terminally elongated forms of amyloid-beta (Aβ) peptides, such as Aβ1–42. Absolute Aβ1–42 levels in CSF have shown diagnostic value for the diagnosis of Alzheimer's disease, but the discrimination among Alzheimer's disease, DLB and PDD was poor. A recently established quantitative urea-based Aβ-sodium-dodecylsulphate–polyacrylamide-gel-electrophoresis with Western immunoblot (Aβ-SDS–PAGE/immunoblot) revealed a highly conserved Aβ peptide pattern of the carboxy-terminally truncated Aβ peptides 1–37, 1–38, 1–39 in addition to 1–40 and 1–42 in human CSF. We used the Aβ-SDS–PAGE/immunoblot to investigate the CSF of 23 patients with Alzheimer's disease, 21 with DLB, 21 with PDD and 23 non-demented disease controls (NDC) for disease-specific alterations of the Aβ peptide patterns in its absolute and relative quantities. The diagnostic groups were matched for age and severity of dementia. The present study is the first attempt to evaluate the meaning of Aβ peptide patterns in CSF for differential diagnosis of the three neurodegenerative diseases—Alzheimer's disease, DLB and PDD. The Aβ peptide patterns displayed disease-specific variations and the ratio of the differentially altered Aβ1–42 to the Aβ1–37 levels subsequently discriminated all diagnostic groups from each other at a highly significant level, except DLB from PDD. Additionally, a novel peptide with Aβ-like immunoreactivity was observed constantly in the CSF of all 88 investigated patients. The pronounced percentage increase of this peptide in DLB allowed a highly significant discrimination from PDD. Using a cut-off point of 0.954%, this marker yielded a diagnostic sensitivity and specificity of 81 and 71%, respectively. From several lines of indication, we consider this peptide to represent an oxidized α-helical form of Aβ1–40 (Aβ1–40^*). The increased abundance of Aβ1–40^* probably reflects a disease-specific alteration of the Aβ1–40 metabolism in DLB. We conclude that Aβ peptide patterns reflect disease-specific pathophysiological pathways of different dementia syndromes as distinct neurochemical phenotypes. Although Aβ peptide patterns failed to fulfil the requirements for a sole biomarker, their combined evaluation with other biomarkers is promising in neurochemical dementia diagnosis. It is noteworthy that DLB and PDD exhibit distinct clinical temporal courses, despite their similar neuropathological appearance. Their distinct molecular phenotypes support the view of different pathophysiological pathways for each of these neurodegenerative diseases.

Can Alzheimer's type pathology influence the clinical phenotype of Parkinson's disease?

OBJECTIVES

Patients with clinical and pathological diagnosis of Parkinson's disease (PD) may, at death, also be found to have the pathological changes of Alzheimer's disease (AD). With this study we aim to determine the influence of AD pathology on the clinical phenotype of PD.

METHODS

We studied 64 patients who donated their brains to the University of Miami Brain Endowment Bank(TM) and fulfilled the clinical and pathological criteria for PD. For the evaluation of AD pathology we used the CERAD criteria. Dementia was diagnosed, in life, also using standard criteria. Case histories were abstracted and reviewed by one investigator (SP) who then made comparisons between patients.

RESULTS

Patients with AD pathology (PD-AD) were older both at the time of diagnosis and death. The presence of AD pathology did not seem to influence disease duration in our cohort of PD patients. As expected there was a clear relation between AD pathology and dementia but not all PD-AD patients were demented. Psychosis and depression were also found to be more prevalent in the PD-AD patients. In the comparison between demented and non-demented PD-AD patients dementia was more likely to appear in patients with PD and definite criteria for AD.

CONCLUSION

Apart from dementia AD pathology seems to be associated with a number of other clinical characteristics of PD.

Lewy body densities in the entorhinal and anterior cingulate cortex predict cognitive deficits in Parkinson's disease

Previous studies reported an association between cortical Lewy body (LB) formation and dementia in Parkinson's disease (PD). However, it is unclear whether cognitive decline in this disorder is related to specific patterns of LB distribution within the cerebral cortex. Moreover, the prediction of cognitive status based on concomitant assessment of LB and Alzheimer's disease lesions has led to conflicting results. We performed a clinicopathological study in 22 elderly PD patients in whom parkinsonism preceded cognitive decline by at least 3 years. Cognitive status was assessed prospectively using the clinical dementia rating scale (CDR); quantitative assessment of LB, neurofibrillary tangles (NFT), and senile plaques (SP) was performed in Brodmann areas 9, 21, 24, 40 and the entorhinal cortex. Statistical analysis was performed using both correlation coefficients and logistic regression models. There was a highly significant correlation between CDR scores and regional LB scores in the entorhinal cortex and area 24. LB and SP densities in the entorhinal cortex accounted for 36.2% and 19.3% of the variability in CDR scores. LB densities in area 24 could explain 25.2% of this variability. NFT densities did not predict cognitive status. In multivariate models only LB densities in the entorhinal cortex and anterior cingulate cortex were significantly associated with CDR scores. These results imply that an assessment of LB pathology limited to the entorhinal cortex and area 24 may be sufficient to predict cognition in PD. They also suggest that LB formation in limbic areas may be crucial for the development of PD dementia.

Prevalence of amyloid-beta deposition in the cerebral cortex in Parkinson's disease

The pathological basis for the dementia which occurs in 20 to 40% of patients with idiopathic Parkinson's disease (PD) remains uncertain. In the present postmortem study, we compared the prevalence and severity of parenchymal and vascular amyloid-beta (Abeta) deposition in the cerebral cortex in a group of 57 PD brains, including 13 cases with dementia, and in 100 control brains. A higher proportion of PD brains had vascular Abeta deposition, whereas the proportions and severity of parenchymal Abeta were similar in the PD and control groups. There was a poor correlation between Abeta deposition and neurofibrillary tangles which were present in only small numbers in a minority of cases. Cortical Abeta deposition was present in only 6 of the 13 cases with dementia and only 3 fulfilled the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) criteria for definite Alzheimer's disease. The present findings confirm that dementia in PD is only infrequently due to fully established Alzheimer's disease. However, vascular and parenchymal Abeta deposition could still contribute to dementia and cognitive decline when combined with other changes such as alpha-synuclein deposition in the cerebral cortex and cortical Lewy bodies.

Simplified neuropathological diagnosis of dementia with Lewy bodies

Pathological criteria have recently been developed to differentiate those cases where Lewy bodies contribute to the dementing process. We applied consensus criteria to 20 cases with a pathological diagnosis of Alzheimer's disease (all demented) and/or Parkinson's disease (three without dementia) and eight controls. In addition, we applied the criteria to the different cortical layers to determine whether the site of the semiquantification affected the diagnosis. In the parietal lobe, few Lewy bodies were observed, and this region could be excluded. Rare Lewy bodies present in the frontal association cortex in a number of Parkinson's disease cases resulted in their classification as limbic or transitional cases with Lewy bodies. Exclusion of this non-limbic association cortex resulted in many of these cases with rare cortical Lewy bodies being re-classified as having brain stem predominant Lewy bodies, thus improving the diagnostic accuracy of the criteria. Most of these cases were non-demented. No other case was re-classified by excluding these cortical regions from the analysis. Few Lewy bodies were present in cortical layers I and II, and these layers could be excluded from the semiquantitative procedure without change to the overall classification of cases. The occasional presence of possible Lewy bodies in cases with Alzheimer's disease and controls incorrectly classified these cases as having brain stem predominant Lewy body disease, although these cases had no brain stem Lewy bodies. These modifications to the consensus criteria for assessing Lewy body disease (i.e. exclude parietal and frontal lobe, cortical layers I and II, and cases without brain stem Lewy bodies), provide significant time and cost savings for neuropathologists and researchers using this criteria to diagnose and study dementia with Lewy bodies.

Dementia with Lewy bodies. A distinct non-Alzheimer dementia syndrome?

Lewy body formation is central to the pathological phenotype of a spectrum of disorders. The most familiar of these is the extrapyramidal syndrome of idiopathic Lewy-body Parkinson's disease (PD). Studies of dementia in the elderly suggest that another manifestation of Lewy body pathology is equally or more common than Parkinson's disease. This syndrome of Dementia with Lewy bodies (DLB) has been given a number of diagnostic labels and is characterised by dementia, relatively mild parkinsonism, visual hallucinations, and fluctuations in conscious level. Although many of these features can arise in Parkinson's disease, the patients with DLB tend to have early neuropsychiatric features which predominate the clinical picture, and the diagnosis of the syndrome in practice is more concerned with the differential diagnosis of Alzheimer's disease (AD). Distinction from AD has clinical importance because of potentially differing therapeutic implications. Diagnostic guidelines for the clinical diagnosis and pathological evaluation of DLB are reviewed. Research into the disorder has centered around characterising the clinical, neuropsychological, pathological, neurochemical and genetic relationships with Alzheimer's disease on the one hand, and Parkinson's disease on the other. Many cases of DLB have prominent pathological features of AD and there are some shared genetic risk factors. Differences from the pathology of PD are predominantly quantitative rather than qualitative and evidence is discussed which suggests that DLB represents a clinicopathological syndrome within the spectrum of Lewy body disorders. The possibility that the syndrome represents a chance association of PD and AD is not supported by published studies.

The relationship of Alzheimer-type pathology to dementia in Parkinson's disease

Lewy body degeneration of the subcortical nuclei other than the substantia nigra is common in PD and may represent the substrate for a higher vulnerability to dementia in patients with PD. Cortical pathologies of Alzheimer and Lewy body type seem to be the major determinants of dementia. The prevalence of Alzheimer's disease is not increased in PD, but "early" cortical Alzheimer lesions (usually sub-clinical in normal controls) are frequently associated with dementia in PD. Furthermore, dementia in PD is heterogeneous and should always prompt the clinician to search for treatable causes.