Alzheimer's disease, Lewy body disease and aging: a comparative study of the perforant pathway

Integrating multi-omics data to reveal the effect of genetic variant rs6430538 on Alzheimer's disease risk

Introduction

Growing evidence highlights a potential genetic overlap between Alzheimer's disease (AD) and Parkinson's disease (PD); however, the role of the PD risk variant rs6430538 in AD remains unclear.

Methods

In Stage 1, we investigated the risk associated with the rs6430538 C allele in seven large-scale AD genome-wide association study (GWAS) cohorts. In Stage 2, we performed expression quantitative trait loci (eQTL) analysis to calculate the cis-regulated effect of rs6430538 on TMEM163 in both AD and neuropathologically normal samples. Stage 3 involved evaluating the differential expression of TMEM163 in 4 brain tissues from AD cases and controls. Finally, in Stage 4, we conducted a transcriptome-wide association study (TWAS) to identify any association between TMEM163 expression and AD.

Results

The results showed that genetic variant rs6430538 C allele might increase the risk of AD. eQTL analysis revealed that rs6430538 up-regulated TMEM163 expression in AD brain tissue, but down-regulated its expression in normal samples. Interestingly, TMEM163 showed differential expression in entorhinal cortex (EC) and temporal cortex (TCX). Furthermore, the TWAS analysis indicated strong associations between TMEM163 and AD in various tissues.

Discussion

In summary, our findings suggest that rs6430538 may influence AD by regulating TMEM163 expression. These discoveries may open up new opportunities for therapeutic strategies targeting AD.

Polygenic risk and pleiotropy in neurodegenerative diseases

In this paper we explore the phenomenon of pleiotropy in neurodegenerative diseases, focusing on Alzheimer's disease (AD). We summarize the various techniques developed to investigate pleiotropy among traits, elaborating in the polygenic risk scores (PRS) analysis. PRS was designed to assess a cumulative effect of a large number of SNPs for association with a disease and, later for disease risk prediction. Since genetic predictions rely on heritability, we discuss SNP-based heritability from genome-wide association studies and its contribution to the prediction accuracy of PRS. We review work examining pleiotropy in neurodegenerative diseases and related phenotypes and biomarkers. We conclude that the exploitation of pleiotropy may aid in the identification of novel genes and provide further insights in the disease mechanisms, and along with PRS analysis, may be advantageous for precision medicine.

Genetic Association Between NGFR, ADAM17 Gene Polymorphism, and Parkinson's Disease in the Chinese Han Population

Parkinson's disease (PD) is a common neurodegenerative disease characterized by neuronal loss in the substantia nigra. The p75 neurotrophin receptor (p75NTR, encoded by NGFR) was found to play an important role in the selective neuronal death of dopamine neurons in the substantia nigra, as well as the pathogenesis and development of PD. To assess the association between NGFR gene polymorphism and the susceptibility of PD, this case-control study consisting of 414 PD patients and 623 age- and sex-matched controls in a Chinese Han cohort was conducted. Twelve tag-single nucleotide polymorphisms (tag-SNPs) were selected from the NGFR gene through the construction of linkage disequilibrium blocks. One tag-SNP from the ADAM17 gene was also selected owing to its function of encoding tumor necrosis factor α-converting enzyme, which is responsible for the shedding of the extracellular domain of p75NTR. A multiplex polymerase chain reaction-ligase detection reaction (PCR-LDR) method was applied for genotyping. The associations between tag-SNPs and the risk of PD with the adjustment for age and sex were analyzed by unconditional logistic regression, and five genetic models including codominant, dominant, recessive, over-dominant, and additive models were applied. The results showed that among the 13 tag-SNPs, rs741073 was associated with a reduced risk of PD in the codominant (OR = 0.71, 95% CI = 0.54-0.93, P = 0.037), dominant (OR = 0.76, 95% CI = 0.58-0.98, P = 0.033), and over-dominant models (OR = 0.71, 95% CI = 0.54-0.92, P = 0.010), and rs1804011 was also associated with a reduced risk of PD in the codominant (OR = 0.69, 95% CI = 0.50-0.95, P = 0.049), dominant (OR = 0.69, 95% CI = 0.50-0.93, P = 0.014), over-dominant (OR = 0.70, 95% CI = 0.51-0.96, P = 0.025), and additive models (OR = 0.72, 95% CI = 0.54-0.94, P = 0.016). However, these associations did not retain after Bonferroni correction. Conclusively, our study failed to reveal the association between the selected tag-SNPs within NGFR, ADAM17, and the susceptibility of PD. The role of p75NTR and its gene polymorphisms in the pathogenesis of PD needs to be further studied.

Clinical and neuropathological features of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is an increasingly recognized entity which overlaps in clinical, pathological and genetic features with Alzheimer's (AD) and Parkinson's disease (PD). Clinically, it is characterized by progressive cognitive impairment with significant fluctuations in alertness, parkinsonism, and psychosis with recurrent hallucinations. The neuropathological hallmarks are the intracytoplasmic inclusions in substantia nigra typical of PD, known as Lewy bodies (LB), but widely distributed throughout paralimbic and neocortical regions. Most of the cases also coexist with a plaque predominant AD. The evidence of alpha-synuclein in LB and related neurites as well as of a synuclein fragment in AD plaques opens new links among these neurodegenerative diseases. This article will review briefly the clinical and pathologicalfeatures that DLB shares with AD and PD, as well as those that support the idea that it is a distinct disorder.

Differential Atrophy of Hippocampal Subfields: A Comparative Study of Dementia with Lewy Bodies and Alzheimer Disease

OBJECTIVES

Dementia with Lewy bodies (DLB) is characterized by relative preservation of the medial temporal lobe compared with Alzheimer disease (AD). The differential involvement of the hippocampal subfields in both diseases has not been clearly established, however. We aim to investigate hippocampal subfield differences in vivo in a clinical cohort of DLB and AD subjects.

METHODS

104 participants (35 DLBs, 36 ADs, and 35 healthy comparison [HC] subjects) underwent clinical assessment and 3T T1-weighted imaging. A Bayesian model implemented in Freesurfer was used to automatically segment the hippocampus and its subfields. We also examined associations between hippocampal subfields and tests of memory function.

RESULTS

Both the AD and DLB groups demonstrated significant atrophy of the total hippocampus relative to HC but the DLB group was characterized by preservation of the cornu ammonis 1 (CA1), fimbria, and fissure. In contrast, all the hippocampal subfields except the fissure were significantly atrophied in AD compared with both DLB and HC groups. Among DLB subjects, CA1 was correlated with the Recent Memory score of the CAMCOG and Delayed Recall subscores of the HVLT.

CONCLUSIONS

DLB is characterized by milder hippocampal atrophy that was accompanied by preservation of the CA1. The CA1 was also associated with memory function in DLB. Our findings highlight the promising role of hippocampal subfield volumetry, particularly that of the CA1, as a biomarker for the distinction between AD and DLB.

Analysis of genome-wide association studies of Alzheimer disease and of Parkinson disease to determine if these 2 diseases share a common genetic risk

IMPORTANCE

Despite Alzheimer disease (AD) and Parkinson disease (PD) being clinically distinct entities, there is a possibility of a pathological overlap, with some genome-wide association (GWA) studies suggesting that the 2 diseases represent a biological continuum. The application of GWA studies to idiopathic forms of AD and PD have identified a number of loci that contain genetic variants that increase the risk of these disorders.

OBJECTIVE

To assess the genetic overlap between PD and AD by testing for the presence of potentially pleiotropic loci in 2 recent GWA studies of PD and AD.

DESIGN

Combined GWA analysis.

SETTING

Data sets from the United Kingdom, Germany, France, and the United States.

PARTICIPANTS

Thousands of patients with AD or PD and their controls.

MAIN OUTCOMES AND MEASURES

Meta-analysis of GWA studies of AD and PD.

METHODS

To identify evidence for potentially pleiotropic alleles that increased the risk for both PD and AD, we performed a combined PD-AD meta-analysis and compared the results with those obtained in the primary GWA studies.We also tested for a net effect of potentially polygenic alleles that were shared by both disorders by performing a polygenic score analysis. Finally, we also performed a gene-based association analysis that was aimed at detecting genes that harbor multiple disease-causing single-nucleotide polymorphisms, some of which confer a risk of PD and some a risk of AD.

RESULTS

Detailed interrogation of the single-nucleotide polymorphism, polygenic, and gene-based analyses resulted in no significant evidence that supported the presence of loci that increase the risk of both PD and AD.

CONCLUSIONS AND RELEVANCE

Our findings therefore imply that loci that increase the risk of both PD and AD are not widespread and that the pathological overlap could instead be “downstream” of the primary susceptibility genes that increase the risk of each disease.

Comparing hippocampal atrophy in Alzheimer's dementia and dementia with lewy bodies

BACKGROUND/AIMS

Dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) are the two most common neurodegenerative dementias. During the early stages, clinical distinction between them is often challenging. Our objective is to compare hippocampal atrophy patterns in mild AD and mild DLB. We hypothesized that DLB subjects have milder hippocampal atrophy relative to AD subjects.

METHODS

We analyzed the T1-weighted magnetic resonance imaging data from 113 subjects: 55 AD, 16 DLB and 42 cognitively normal elderly (normal controls, NC). Using the hippocampal radial distance technique and multiple linear regression, we analyzed the effect of clinical diagnosis on hippocampal radial distance, while adjusting for gender and age. Three-dimensional statistical maps were adjusted for multiple comparisons using permutation-based statistics with a threshold of p < 0.01.

RESULTS

Compared to NC, AD exhibited significantly greater atrophy in the cornu ammonis (CA)1, CA2-3 and subicular regions bilaterally while DLB showed left-predominant atrophy in the CA1 region and subiculum. Compared directly, AD and DLB did not reveal statistically significant differences.

CONCLUSION

Hippocampal atrophy, while present in mildly impaired DLB subjects, is less severe than atrophy seen in mildly impaired AD subjects, when compared to NC. Both groups show predominant atrophy of the CA1 subfield and subiculum.

Review: disruption of the postsynaptic density in Alzheimer's disease and other neurodegenerative dementias

The most common causes of neurodegenerative dementia include Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). We believe that, in all 3, aggregates of pathogenic proteins are pathological substrates which are associated with a loss of synaptic function/plasticity. The synaptic plasticity relies on the normal integration of glutamate receptors at the postsynaptic density (PSD). The PSD organizes synaptic proteins to mediate the functional and structural plasticity of the excitatory synapse and to maintain synaptic homeostasis. Here, we will discuss the relevant disruption of the protein network at the PSD in these dementias and the accumulation of the pathological changes at the PSD years before clinical symptoms. We suggest that the functional and structural plasticity changes of the PSD may contribute to the loss of molecular homeostasis within the synapse (and contribute to early symptoms) in these dementias.

Neuritic pathology as a correlate of synaptic loss in dementia with lewy bodies

Synaptic loss is present in Alzheimer's disease and correlates with the severity of dementia. Loss of synapses in dementia with Lewy bodies (DLB) does not correlate as clearly with cognitive status and its cause is unclear. To begin to understand the relationship between cognition and synaptic loss in DLB, we assessed immunoreactivity for the synaptic-terminal specific protein, synaptophysin, in the hippocampus in 14 DLB cases. Quantitative synaptic data were obtained using an Image-Pro semiautomated analysis system. We determined Braak stage, beta-amyloid, Lewy bodies (LBs), and Lewy neurites (LN). We found significant correlations (r = 0.617, P < .01) between Braak stage and synaptophysin score and marginal correlation between LN score and synaptophysin loss ( r = 0.694, P < .06). Correlations of beta-amyloid and of LB density with synaptophysin score were unimpressive. These data support the hypothesis that synaptic loss in DLB is related to neuritic degeneration.

Dementia with Lewy bodies

The advent of new immunostains have improved the ability to detect limbic and cortical Lewy bodies, and it is evident that dementia with Lewy bodies (DLB) is the second most common neurodegenerative dementia, after Alzheimer's disease (AD). Distinguishing DLB from AD has important implications for treatment, in terms of substances that may worsen symptoms and those that may improve them. Neurocognitive patterns, psychiatric features, extrapyramidal signs, and sleep disturbance are helpful in differentiating DLB from AD early in the disease course. Differences in the severity of cholinergic depletion and type/distribution of neuropathology contribute to these clinical differences.

Clinical and neuropathological correlates of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is characterized pathologically by widespread Lewy body (LB) neuronal inclusions in the brain, but the contribution of LBs to the clinical syndrome of dementia and parkinsonism is unclear. In a clinical-pathological study of 25 cases with DLB, we examined the regional neuroanatomical distribution of Lewy-related pathology using alpha-synuclein immunostaining to evaluate the relationship between LBs, neuronal loss, Alzheimer-type changes, and the clinical phenotype. Compared to traditional ubiquitin immunostaining, alpha-synuclein immunohistochemistry was more specific and slightly more sensitive, staining about 5% more intracytoplasmic structures. There was a consistent pattern of vulnerability to LB formation across subcortical, paralimbic, limbic, and neocortical structures, which was independent of concomitant Alzheimer-type changes. There were no significant differences in regional LB densities among patients with or without cognitive fluctuations, visual hallucinations, delusions, recurrent falls or parkinsonism. Duration of disease correlated weakly with LB density. There was no neuronal loss in superior temporal sulcus or entorhinal cortex in pure DLB cases compared to nondemented controls. Thus, DLB is characterized by a specific neuroanatomical vulnerability to LB pathology, distinct from AD pathology, with a complicated relationship to clinical symptoms.

Clinical and pathologic features of two groups of patients with dementia with Lewy bodies: effect of coexisting Alzheimer-type lesion load

The objectives of this study were to examine the clinical and pathologic features of two subgroups of patients with dementia with Lewy bodies (DLB) differing in Alzheimer disease (AD)-type pathology load and to identify clinical variables useful in the differential diagnosis from AD. The records of 64 consecutive demented patients were reviewed. Pathologic diagnoses were independently established [35 AD cases, 11 cases of pure dementia with Lewy bodies (pDLB), and 18 cases of combined AD plus Lewy bodies (AD+LB)], and several neurodegenerative lesions were quantified. Clinical and pathologic data were compared between groups with univariate and multivariate analyses. Compared with the other groups, pDLB cases had more frequent acute-subacute onset of dementia [45% vs. AD (3%) and AD+LB (16%)], early parkinsonism [45% vs. AD (0%) and AD+LB (0%)], early [27% vs. AD (0%) and AD+LB (0%)] and late [73% vs. AD (11%) and AD+LB (16%)] hallucinations, fluctuating course [46% vs. AD (9%) and AD+LB (22%)], delusions [45% vs. AD (11%) and AD+LB (6%)], spontaneous parkinsonism [63% vs. AD (8%) and AD+LB (16%)], less frequent ideomotor apraxia and loss of insight, earlier urinary incontinence [3.2 +/- 1.4 years after onset vs. AD (6.3 years) and AD+LB (5.8 years)], shorter duration of dementia [7.7 +/- 2.4 years vs. AD (9.6 years) and AD+LB (11 years)], milder atrophy in computed tomography scans, greater brain weight, more transcortical spongiosis, wider cortex and subcortex, and less amyloid angiopathy. All pDLB cases but no AD cases had abnormal CA2 neurites. The clinical features of AD+LB patients were similar to those of AD patients other than more frequent acute-subacute onset and fluctuating evolution. Discriminant analyses selected four clinical variables differentiating pDLB from the other two groups as a whole: acute-subacute onset, early parkinsonism, early hallucinations, and early onset of urinary incontinence. Two or more of these features identified pDLB with a sensitivity of 81.8% and a specificity of 95.9%. Differentiation between the three groups (pDLB, AD+LB, and AD) or between both groups with LB (DLB) from AD could be only attained in 70% of cases. We conclude that early symptomatology is the main clue for the diagnosis of pDLB. We identified by discriminant analysis a set of clinical diagnostic criteria similar to those proposed by the Consortium on Dementia With Lewy Bodies. Accuracy was excellent for the diagnosis of pDLB but only mediocre for separating AD+LB as well as the entire DLB group from AD.

Frontotemporal dementia with ubiquitinated inclusions: A case study of the regional distribution of hippocampal pathology

In motor neuron disease (MND) cases associated with dementia, neurons often contain ubiquitin-positive, taunegative cytoplasmic inclusions that are numerous in the granule cell neurons of the hippocampal complex. Dot or threadlike ubiquitinated neurites are also observed in the surrounding neuropil and in other frontotemporal regions. Cases of frontotemporal dementia (FTD) with identical appearing ubiquitinated deposits have been described in FTD cases lacking signs of MND. The underlying pathobiology of these cases remains obscure. We describe a case from a familial FTD kindred and use immunohistochemistry to evaluate the hippocampal ubiquitin-positive cytoplasmic granule cell inclusions in relationship to the threads and dots that surround them. Ubiquitin-positive threads were more numerous in the overlying molecular layer of the dentate gyrus (DG) compared with the underlying polymorphic layer, suggesting that threads are formed primarily in the dendrites of the affected granule cells. In contrast, dot-like inclusions were uniformly distributed. Using antibodies to synapticterminal specific proteins, we observed loss of perforant pathway synapses in the outer molecular layer of the DG. The numbers of thread-and dot-like inclusions were no greater in the region of synaptic loss than in the layer that lacked detectable synaptic loss. Similarly, ubiquitinated aggregates were more numerous in rostral sections, and they tended to cluster, whereas synapse loss was uniform. These findings expand upon previous data by suggesting that formation of these ubiquitinated aggregates relate to an inherent susceptibility in the granule cell neuron, rather than solely to a deafferentation effect. This study contributes to our understanding of what might be a common pathological process underlying FTD and MND cases with ubiquitinated inclusions.

Dementia with Lewy bodies

In the last decade, a new degenerative dementia, probably the second most common after Alzheimer's disease (AD), has been increasingly recognized under the consensus name of dementia with Lewy bodies (DLB). This article reviews current clinical, genetic, and pathological DLB data and indicates directions for future research. DLB overlaps in clinical, pathological, and genetic features with AD and Parkinson's disease (PD). Clinically, it is characterized by progressive cognitive impairment with significant fluctuations in alertness, parkinsonism, and psychosis with recurrent hallucinations. The neuropathological hallmarks are the intracytoplasmic inclusions in substantia nigra typical of PD, known as Lewy bodies (LB) but distributed widely throughout paralimbic and neocortical regions. Most of the cases also coexist with a plaque predominant AD. It is probably the unique and differential distribution of the lesions throughout cortical and subcortical structures in each of these disorders that supports a specific clinical syndrome and may ultimately prove most useful in understanding their different etiologies. Several genes have recently been implicated in LB formation. Special interest arises from mutations in the alpha-synuclein gene, which appears to be responsible for autosomal dominant PD in several kindreds. This gene encodes a presynaptic protein, a fragment of which is present in AD plaques. Recent studies show intense and quite specific alpha-synuclein immunoreactivity in LB and related neurites, suggesting a potential role of this protein in the aggregation or precipitation of LB inclusions.

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 medial temporal lobe in dementia with Lewy bodies: a comparative study with Alzheimer's disease

The usefulness of determining medial temporal lobe (MTL) size in differentiating Alzheimer's disease (AD) from other dementia subtypes is unknown. We compared the cross-sectional areas of the MTLs in histological sections from the brains of 18 patients with dementia with Lewy bodies (DLB) but lacking AD changes, 24 DLB patients with concurrent AD pathology, 20 pure AD cases, and 18 age-matched control cases. Duration and severity of disease were comparable between groups. When data for cross-sectional area were expressed as percentages of the average control area, DLB MTLs were significantly larger than either AD or DLB/AD MTLs at rostral levels (86 +/- 16%, 54 +/- 17%, and 66 +/- 23% of control areas, respectively). At caudal levels, DLB MTLs were larger than AD MTLs (80 +/- 20%, 59 +/- 21%, and 77 +/- 26% of control areas in DLB, AD, and DLB/AD, respectively). MTL cross-sectional area often approaches normal in pure DLB, even when disease duration is prolonged and symptoms are end stage. In contrast, a greatly reduced MTL area mitigates against the diagnosis of DLB, unless there are concurrent AD changes.