Gray matter structural covariance networks patterns associated with autopsy-confirmed LATE-NC compared to Alzheimer's disease pathology

BACKGROUND

Cases with the limbic-predominant age-related TAR DNA-binding protein 43 (TDP-43) encephalopathy neuropathologic change (LATE-NC), Alzheimer's disease (AD), and mixed AD+TDP-43 pathology (AD+LATE-NC) share similar symptoms, which makes it a challenge for accurate diagnosis. Exploring the patterns of gray matter structural covariance networks (SCNs) in these three types may help to clarify the underlying mechanism and provide a basis for clinical interventions.

METHODS

We included ante-mortem MRI data of 10 LATE-NC, 39  AD, and 25  AD+LATE-NC from the ADNI autopsy sample. We used four regions of interest (left posterior cingulate cortex, right entorhinal cortex, frontoinsular and dorsolateral prefrontal cortex) to anchor the default mode network (DMN), salience network (SN), and executive control network (ECN). Finally, we assessed the SCN alternations using a multi-regression model-based linear-interaction analysis.

RESULTS

Cases with autopsy-confirmed LATE-NC and AD showed increased structural associations involving DMN, ECN, and SN. Cases with AD+LATE-NC showed increased structural association within DMN while decreased structural association between DMN and ECN. The volume of peak clusters showed significant associations with cognition and AD pathology.

CONCLUSIONS

This study showed different SCN patterns in the cases with LATE-NC, AD, and AD+LATE-NC, and indicated the network disconnection mechanism underlying these three neuropathological progressions. Further, SCN may serve as an effective biomarker to distinguish between different types of dementia.

Vascular pathology and pathogenesis of cognitive impairment and dementia in older adults

It is well recognized that brains of older people often harbor cerebrovascular disease pathology including vessel disease and vascular-related tissue injuries and that this is associated with vascular cognitive impairment and contributes to dementia. Here we review vascular pathologies, cognitive impairment, and dementia. We highlight the importance of mixed co-morbid AD/non-AD neurodegenerative and vascular pathology that has been collected in multiple clinical pathologic studies, especially in community-based studies. We also provide an update of vascular pathologies from the Rush Memory and Aging Project and Religious Orders Study cohorts with special emphasis on the differences across age in persons with and without dementia. Finally, we discuss neuropathological perspectives on the interpretation of clinical-pathological studies and emerging data in community-based studies.

Analysis of genes (TMEM106B, GRN, ABCC9, KCNMB2, and APOE) implicated in risk for LATE-NC and hippocampal sclerosis provides pathogenetic insights: a retrospective genetic association study

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is the most prevalent subtype of TDP-43 proteinopathy, affecting up to 1/3rd of aged persons. LATE-NC often co-occurs with hippocampal sclerosis (HS) pathology. It is currently unknown why some individuals with LATE-NC develop HS while others do not, but genetics may play a role. Previous studies found associations between LATE-NC phenotypes and specific genes: TMEM106B, GRN, ABCC9, KCNMB2, and APOE. Data from research participants with genomic and autopsy measures from the National Alzheimer’s Coordinating Center (NACC; n = 631 subjects included) and the Religious Orders Study and Memory and the Rush Aging Project (ROSMAP; n = 780 included) were analyzed in the current study. Our goals were to reevaluate disease-associated genetic variants using newly collected data and to query whether the specific genotype/phenotype associations could provide new insights into disease-driving pathways. Research subjects included in prior LATE/HS genome-wide association studies (GWAS) were excluded. Single nucleotide variants (SNVs) within 10 kb of TMEM106B, GRN, ABCC9, KCNMB2, and APOE were tested for association with HS and LATE-NC, and separately for Alzheimer’s pathologies, i.e. amyloid plaques and neurofibrillary tangles. Significantly associated SNVs were identified. When results were meta-analyzed, TMEM106B, GRN, and APOE had significant gene-based associations with both LATE and HS, whereas ABCC9 had significant associations with HS only. In a sensitivity analysis limited to LATE-NC + cases, ABCC9 variants were again associated with HS. By contrast, the associations of TMEM106B, GRN, and APOE with HS were attenuated when adjusting for TDP-43 proteinopathy, indicating that these genes may be associated primarily with TDP-43 proteinopathy. None of these genes except APOE appeared to be associated with Alzheimer’s-type pathology. In summary, using data not included in prior studies of LATE or HS genomics, we replicated several previously reported gene-based associations and found novel evidence that specific risk alleles can differentially affect LATE-NC and HS.

Sex differences in mixed neuropathologies in community-dwelling older adults

Alzheimer's dementia is the leading cause of dementia in older adults and women are disproportionately burdened. It is increasingly recognized that dementia in older persons is related to the co-occurrence of mixed pathologies in the brain, but few studies have examined whether the frequency of common pathologies vary by sex. We examined the frequency of the most common mixed pathologies that underlie Alzheimer's dementia in aging, including Alzheimer's disease (AD) in combination with Lewy Bodies, cerebrovascular disease (CVD) pathology, or TDP-43/Hippocampal sclerosis, and determined whether the patterns differed for women and men in a combined cohort of over 1500 older community-dwelling adults. We found in separate models that women were significantly more likely to have AD and CVD pathology than men, and men were more likely to have "pure" Lewy Body disease, in models adjusted for age at death, education, race, and the APOE-e4 allele. Although AD with TDP-43/Hippocampal sclerosis pathology was greater in number in women than men, the difference was not significant after adjustments for age at death and other confounders. Together these findings suggest sex differences in mixed pathology, specifically AD with CVD in older adults from the community.

Relationship Between Tau, β Amyloid and α-Synuclein Pathologies

It is becoming increasing clear that multiple pathological lesions co-exist in the brains of the demented and non-demented elderly, and with putative interactions revealed at the molecular level in addition to the cumulative effects on brain damage, mounting evidence suggests manifestation of multiple protein aggregates will have implications for the clinical course of many neurodegenerative diseases associated with dementia. In this section we will discuss how the presence of multiple pathological lesions can affect the pathological and clinical phenotype of neurodegenerative disorders.

Improving the identification of dementia with Lewy bodies in the context of an Alzheimer's-type dementia

BACKGROUND

Dementia due to Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) are the two most common neurodegenerative causes of dementia. They commonly occur together, especially in older people, but clinical identification of these diseases in dementia is difficult in such circumstances. We therefore conducted a study using cases with both comprehensive prospective clinical assessments and complete neuropathological examination to determine if it is possible to identify such mixed cases clinically and to determine features which may identify DLB in the presence of AD dementia.

METHODS

At Newcastle Brain Bank we identified subjects who had a clinical diagnosis of dementia and who also had autopsy diagnoses of pure AD, pure DLB, or mixed AD+DLB. All subjects had undergone prospective longitudinal clinical assessments. Mixed AD+DLB patients met neuropathological criteria for both DLB (limbic/neocortical Lewy body disease) and AD (Braak stage V/VI and CERAD B/C). The records of these subjects were carefully reviewed by two specialists in old-age psychiatry blind to autopsy findings to determine baseline and final clinical diagnoses based on these detailed records. The presence of characteristic Lewy body symptoms and other clinical information was also recorded.

RESULTS

Of 59 subjects included, 19 were AD, 18 DLB, and 22 mixed AD+DLB. At baseline no subjects were correctly identified as having mixed AD+DLB and by final diagnosis only 23% were identified. The only symptom which helped in identifying the presence of Lewy body disease in the context of a mixed AD+DLB dementia was complex visual hallucinations.

CONCLUSIONS

Whilst the identification of DLB in the context of a dementia with an AD pattern is difficult, the emergence of complex visual hallucinations in the context of such a degenerative dementia suggests the presence of Lewy body disease and should encourage a careful assessment. Biomarkers appear likely to be necessary to help improve identification of different disease subtypes underlying dementia.