Genetics in degenerative dementia: current status and applicability

The role of ATP-binding cassette transporter G1 (ABCG1) in Alzheimer's disease: A review of the mechanisms

The maintenance of cholesterol homeostasis is essential for central nervous system function. Consequently, factors that affect cholesterol homeostasis are linked to neurological disorders and pathologies. Among them, ATP-binding cassette transporter G1 (ABCG1) plays a significant role in atherosclerosis. However, its role in Alzheimer's disease (AD) is unclear. There is inconsistent information regarding ABCG1's role in AD. It can increase or decrease amyloid β (Aβ) levels in animals' brains. Clinical studies show that ABCG1 is involved in AD patients' impairment of cholesterol efflux capacity (CEC) in the cerebrospinal fluid (CSF). Lower Aβ levels in the CSF are correlated with ABCG1-mediated CEC dysfunction. ABCG1 modulates α-, β-, and γ-secretase activities in the plasma membrane and may affect Aβ production in the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) cell compartment. Despite contradictory findings regarding ABCG1's role in AD, this review shows that ABCG1 has a role in Aβ generation via modulation of membrane secretases. It is, however, necessary to investigate the underlying mechanism(s). ABCG1 may also contribute to AD pathology through its role in apoptosis and oxidative stress. As a result, ABCG1 plays a role in AD and is a candidate for drug development.

Distinct impaired patterns of intrinsic functional network centrality in patients with early- and late-onset Alzheimer's disease

Early-onset Alzheimer's disease (EOAD) involves multiple cognitive domains and shows more rapid progression than late-onset Alzheimer's disease (LOAD). However, the difference in pathogenesis between EOAD and LOAD is still unclear. Accordingly, we applied intrinsic network analysis to explore the potential neuropathological mechanism underlying distinct clinical phenotypes. According to the cut-off age of 65, we included 20 EOAD patients, 20 LOAD patients, and 36 age-matched controls (19 young and 17 old controls). We employed resting-state functional MRI and network centrality analysis to explore the local (degree centrality (DC)) and global (eigenvector centrality (EC)) functional integrity. Two-sample t-test analysis was performed, with gray matter volume, age, gender, and education as covariates. Furthermore, we performed a correlation analysis between network metrics and cognition. Compared to young controls, EOAD patients exhibited lower DC in the middle temporal gyrus (MTG), parahippocampal gyrus (PHG), superior temporal gyrus (STG), and lower EC in the MTG, PHG, and postcentral gyrus. In contrast, LOAD patients exhibited lower DC in the STG and anterior cingulum gyrus and higher DC in the middle frontal gyrus compared to old controls. No significant difference in EC was observed in LOAD patients. Furthermore, both DC and EC correlated with cognitive performance. Our study demonstrated divergent functional network impairments in EOAD and LOAD patients. EOAD patients showed more complex network damage involving both local and global centrality properties, while LOAD patients mainly featured local functional connectivity changes. Such centrality impairments are related to poor cognition, especially regarding memory performance.

Role of TREM2 in Alzheimer's Disease and its Consequences on β- Amyloid, Tau and Neurofibrillary Tangles

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Alzheimer's Disease (AD) is age-related neurodegenerative disorder recognized by a steadily gradual cognitive decline that has devastating personal and socioeconomic implications. Recently, some genetic factors for AD have been identified which attracted wide attention of researchers in different areas of AD biology and possible new therapeutic targets. Alternative forms of triggering receptor expressed on myeloid cells 2 (TREM2) genes are examples of such risk factors, which contribute higher risk for developing AD. Comprehending TREM2 function pledge to provide salient insight into how neuroinflammation contributes to AD pathology. The dearth of microglial TREM2 shepherd to augmented tau pathology is couple with frequent enhancement of activated neuronal stress kinases. The involvement of TREM2 in the regulation of tau-associated innate immune response of the CNS has clearly demonstrated through these findings. However, whether decrease level of TREM2 assists pathology of tau through changed clearance and pathological escalation of tau or through direct contact between microglia and neuron and any alternative possible mechanisms need to examine. This review briefly summarizes distinct functional roles of TREM2 in AD pathology and highlights the TREM2 gene regulation. We have also addressed the impact of TREM2 on β-amyloid plaques and tau pathology in Alzheimer’s disease.

Intermittent Fasting Protects against Alzheimer's Disease Possible through Restoring Aquaporin-4 Polarity

The impairment of amyloid-β (Aβ) clearance in the brain plays a causative role in Alzheimer's disease (AD). Polarity distribution of aquaporin-4 (AQP4) is important to remove Aβ from brain. AQP4 polarity can be influenced by the ratio of two AQP4 isoforms M1 and M23 (AQP4-M1/M23), however, it is unknown whether the ratio of AQP4-M1/M23 changes in AD. Histone deacetylase 3 has been reported to be significantly increased in AD brain. Moreover, evidence indicated that microRNA-130a (miR-130a) possibly mediates the regulation of histone deacetylase 3 on AQP4-M1/M23 ratio by repressing the transcriptional activity of AQP4-M1 in AD. This study aimed to investigate whether intermittent fasting (IF), increasing the level of an endogenous histone deacetylases inhibitor β-hydroxybutyrate, restores AQP4 polarity via miR-130a mediated reduction of AQP4-M1/M23 ratio in protection against AD. The results showed that IF ameliorated cognitive dysfunction, prevented brain from Aβ deposition, and restored the AQP4 polarity in a mouse model of AD (APP/PS1 double-transgenic mice). Additionally, IF down-regulated the expression of AQP4-M1 and histone deacetylase 3, reduced AQP4-M1/M23 ratio, and increased miR-130a expression in the cerebral cortex of APP/PS1 mice. In vitro, β-hydroxybutyrate was found to down-regulate the expression of AQP4-M1 and histone deacetylase 3, reduce AQP4-M1/M23 ratio, and increase AQP4-M23 and miR-130a expression in 2 μM Aβ-treated U251 cells. Interestingly, on the contrary to the result observed in 2 μM Aβ-treated cells, AQP4 expression was obviously decreased in cells exposed to 10 μM Aβ. miR-130a mimic decreased the expression of AQP4-M1 and the ratio of AQP4-M1/M23, as well as silencing histone deacetylase 3 caused the up-regulation of AQP4 and miR-130a, and the reduction of AQP4-M1/M23 ratio in U251 cells. In conclusion, IF exhibits beneficial effects against AD. The mechanism may be associated with recovery of AQP4 polarity, resulting from the reduction of AQP4-M1/M23 ratio. Furthermore, β-hydroxybutyrate may partly mediate the effect of IF on the reduction of AQP4-M1/M23 ratio in AD, in which miR-130a and histone deacetylase 3 may be implicated.

Associations between APOE polymorphisms and seven diseases with cognitive impairment including Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies in southeast China

Supplemental Digital Content is available in the text.

Objective

To explore the effect of APOE polymorphisms on patients with cognitive impairments in The Chinese Han population.

Materials and methods

A total of 1027 cases with Alzheimer’s disease (AD), 40 cases with vascular dementia (VaD), 28 cases with behavioral variant frontotemporal dementia (bvFTD), 54 cases with semantic dementia (SD), 44 cases with dementia with Lewy bodies (DLB), 583 cases with mild cognitive impairment (MCI), and 32 cases with vascular cognitive impairment no dementia (VCIND) were recruited consecutively from memory disorders clinics in Huashan Hospital between January 2010 and December 2014. The 1149 cognitively normal controls were recruited from the community epidemiologic investigations. The APOE genotypes were determined using the TaqMan assay.

Results

The distribution of genotype and allele frequencies of APOE differed significantly between control and AD or MCI, with ε4 increasing the risk of AD and MCI in a dose-dependent pattern and ε2 decreasing the risk of AD, but not the risk of MCI. As for VaD, significant differences in the APOE genotype distribution were found compared with the controls. E4/4 increased the risk of VaD and ε4 increased the risk of VCIND in women. The allele distribution differed between bvFTD and controls, but genotype and allele frequencies of APOE did not affect the risk of bvFTD, SD, and DLB.

Conclusion

In The Chinese Han population, APOE ε4 increased the risk of AD and MCI in a dose-dependent manner and ε2 decreased the risk of AD as reported previously. APOEε4 might increase risk in VaD and female patients with VCIND, but no effects of APOE on bvFTD, DLB, and SD were found.

Genetic Counseling and Testing for Alzheimer's Disease and Frontotemporal Lobar Degeneration: An Italian Consensus Protocol

BACKGROUND

Genetic testing of familial Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) is attracting interest thanks to innovative primary prevention clinical trials and increased request for information by at-risk individuals. However, ethical, social, and psychological implications are paramount and genetic testing must be supported by structured genetic counseling. In Italy, practice parameters and guidelines for genetic counseling in dementia are not available.

OBJECTIVE

To develop a nationally harmonized protocol for genetic counseling and testing of familial AD and FTLD.

METHODS

Activities were carried out in the context of the Italian Dominantly Inherited Alzheimer's and Frontotemporal Network (IT-DIAfN) project, a national network of centers of excellence with expertise in managing patients with familial AD and FTLD. A survey of the literature on genetic counseling protocols and guidelines was conducted. Local protocols for genetic counseling were surveyed. Differences and commonalities among protocols were identified and discussed among project partners. Consensus was reached following implicit aggregation methods.

RESULTS

Consensus was reached on a protocol for patients with clinically diagnosed familial AD or FTLD and a distinct protocol for their at-risk relatives. Genetic counseling should be provided by a multidisciplinary team including a geneticist, a neurologist/geriatrician, and a psychologist/psychiatrist, according to the following schedule: (i) initial consultation with tailored information on the genetics of the dementias; (ii) clinical, psychological, and cognitive assessment; if deemed appropriate (iii) genetic testing following a structured decision tree for gene mutation search; (iv) genetic testing result disclosure; (v) psychological support follow-up.

CONCLUSION

This genetic counseling protocol provides Italian centers with a line of shared practice for dealing with the requests for genetic testing for familial AD and FTLD from patients and at-risk relatives, who may also be eligible participants for novel prevention clinical trials.

Integrated late onset Alzheimer's disease (LOAD) susceptibility genes: Cholesterol metabolism and trafficking perspectives

Late onset Alzheimer's disease (LOAD) is the most common type of dementia and is characterized by decreased amyloid-β (Aβ) clearance from the brain. Cholesterol regulates the production and clearance of Aβ. Genome-wide association study (GWAS) suggests that at least 20 genes are associated with LOAD. The genes APOE, CLU, SORL1, PICALM, and BIN1 have a relatively high LOAD susceptibility. Additional experimental and bioinformatic approaches to integrate data from genetics, epigenetics, and molecular networks may further increase our understanding of LOAD in relation to cholesterol metabolism and trafficking.

Frontotemporal Dementia: An Updated Clinician's Guide

Today, frontotemporal dementia (FTD) remains one of the most common forms of early-onset dementia, that is, before the age of 65, thus posing several diagnostic challenges to clinicians since symptoms are often mistaken for psychiatric or neurological diseases causing a delay in correct diagnosis, and the majority of patients with FTD present with symptoms at ages between 50 and 60. Genetic components are established risk factors for FTD, but the influence of lifestyle, comorbidity, and environmental factors on the risk of FTD is still unclear. Approximately 40% of individuals with FTD have a family history of dementia but less than 10% have a clear autosomal dominant pattern of inheritance. Lack of insight is often an early clue to FTD. A tailored treatment option at an early phase can mitigate suffering and improve patients' and caregivers' quality of life.

Socio-Genomics and Structural Competency

Adverse developmental exposures and pathologies of the social environment make vastly greater contributions to the leading health burdens in society than currently known genotypic information. Yet, while patients now commonly bring information on single alleles to the attention of their healthcare team, the former conditions are only rarely considered with respect to future health outcomes. This manuscript aims to integrate social environmental influences in genetic predictive models of disease risk. Healthcare providers must be educated to better understand genetic risks for complex diseases and the specific health consequences of societal adversities, to facilitate patient education, disease prevention, and the optimal care in order to achieve positive health outcomes for those with early trauma or other social disadvantage.

Current directions in behavioral medicine research on genetic testing for disease susceptibility: introduction to the special section

The aim of this special section is to showcase research contributing to our understanding of factors influencing decisions to undergo genetic testing and the impact of the genetic testing process on health-related behaviors of tested individuals. The first two articles report studies investigating factors associated with interest in genetic testing and acceptance of test results (Sherman et al. in J Behav Med doi: 10.1007/s10865-015-9630-9 , 2015; Taber et al. in J Behav Med doi: 10.1007/s10865-015-9642-5 , 2015b). The next two papers address the unique contribution of genetic risk information to understanding risk beyond genetic counseling alone (Heiniger et al. in J Behav Med doi 10.1007/s10865-015-9632-7 , 2015; Taber et al. in J Behav Med doi: 10.1007/s10865-015-9648-z , 2015a). The final three articles investigate the effects of genetic risk information on beliefs about disease control and prevention (Aspinwall et al. in J Behav Med doi: 10.1007/s10865-015-9631-8 , 2015; Kelly et al. in J Behav Med doi 10.1007/s10865-014-9613-2 , 2014; Myers et al. in J Behav Med doi: 10.1007/s10865-015-9626-5 , 2015). Collectively, the special section of papers highlights the diverse ways in which behavioural medicine contributes to our understanding of genetic testing for disease risk, and points to the value of further research to better understand ways in which individuals perceive, interpret and respond to genetic risk information.

Clearance systems in the brain-implications for Alzheimer disease

Accumulation of toxic protein aggregates-amyloid-β (Aβ) plaques and hyperphosphorylated tau tangles-is the pathological hallmark of Alzheimer disease (AD). Aβ accumulation has been hypothesized to result from an imbalance between Aβ production and clearance; indeed, Aβ clearance seems to be impaired in both early and late forms of AD. To develop efficient strategies to slow down or halt AD, it is critical to understand how Aβ is cleared from the brain. Extracellular Aβ deposits can be removed from the brain by various clearance systems, most importantly, transport across the blood-brain barrier. Findings from the past few years suggest that astroglial-mediated interstitial fluid (ISF) bulk flow, known as the glymphatic system, might contribute to a larger portion of extracellular Aβ (eAβ) clearance than previously thought. The meningeal lymphatic vessels, discovered in 2015, might provide another clearance route. Because these clearance systems act together to drive eAβ from the brain, any alteration to their function could contribute to AD. An understanding of Aβ clearance might provide strategies to reduce excess Aβ deposits and delay, or even prevent, disease onset. In this Review, we describe the clearance systems of the brain as they relate to proteins implicated in AD pathology, with the main focus on Aβ.

Arizona Study of Aging and Neurodegenerative Disorders and Brain and Body Donation Program

The Brain and Body Donation Program (BBDP) at Banner Sun Health Research Institute (http://www.brainandbodydonationprogram.org) started in 1987 with brain-only donations and currently has banked more than 1600 brains. More than 430 whole-body donations have been received since this service was commenced in 2005. The collective academic output of the BBDP is now described as the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND). Most BBDP subjects are enrolled as cognitively normal volunteers residing in the retirement communities of metropolitan Phoenix, Arizona. Specific recruitment efforts are also directed at subjects with Alzheimer's disease, Parkinson's disease and cancer. The median age at death is 82. Subjects receive standardized general medical, neurological, neuropsychological and movement disorders assessments during life and more than 90% receive full pathological examinations by medically licensed pathologists after death. The Program has been funded through a combination of internal, federal and state of Arizona grants as well as user fees and pharmaceutical industry collaborations. Subsets of the Program are utilized by the US National Institute on Aging Arizona Alzheimer's Disease Core Center and the US National Institute of Neurological Disorders and Stroke National Brain and Tissue Resource for Parkinson's Disease and Related Disorders. Substantial funding has also been received from the Michael J. Fox Foundation for Parkinson's Research. The Program has made rapid autopsy a priority, with a 3.0-hour median post-mortem interval for the entire collection. The median RNA Integrity Number (RIN) for frozen brain and body tissue is 8.9 and 7.4, respectively. More than 2500 tissue requests have been served and currently about 200 are served annually. These requests have been made by more than 400 investigators located in 32 US states and 15 countries. Tissue from the BBDP has contributed to more than 350 publications and more than 200 grant-funded projects.

APOE Genotype Affects Cognitive Training Response in Healthy Shanghai Community-Dwelling Elderly Individuals

BACKGROUND

Cognitive training may contribute to the ability to maintain cognitive function in healthy elderly adults. Whether genotype modifies training effects remains unknown.

OBJECTIVE

Assess influence of APOE on cognitive function over time in community-dwelling elderly adults participating in multi-domain cognitive training.

METHODS

Healthy individuals ≥70 years of age were screened from one urban community in Shanghai. 145 healthy Chinese older adults met inclusion criteria and were assigned to intervention (n = 88) or control (n = 57) groups. Multi-domain cognitive training involved 24 sessions of different content taking place over 12 weeks. Neuropsychological testing was administered at baseline, immediately after training, six months and twelve months post-intervention; composite measures of cognitive function were identified via factor analysis.

RESULTS

Three factors explained the majority of variance in function (verbal memory, processing speed, executive function). The intervention attenuated 12-month declines in processing speed, regardless of APOE genotype (p = 0.047). Executive function declined in APOEɛ4 carriers over 12 months, regardless of intervention (p = 0.056). There was a significant interaction after 12 months where intervention ɛ4 carriers had better processing speed than ɛ4 controls (p = 0.003). Intervention ɛ2 carriers had better executive function immediately after training (p = 0.02) and had better verbal memory 6-months post-intervention (p = 0.04). These effects remained significant after false-discovery rate correction.

CONCLUSION

Multi-domain cognitive training reduces declines in processing speed over time. APOEɛ4 is associated with reductions in executive function over time, and training may attenuate ɛ4-associated declines in processing speed. APOEɛ2 carriers may also benefit from training, particularly on measures of executive function and verbal memory.

The Role of TREM2 in Alzheimer's Disease and Other Neurological Disorders

Alzheimer's disease (AD) is the leading cause of dementia worldwide. Late-onset AD (LOAD), is the most common form of Alzheimer's disease, representing about >95% of cases and early-onset AD represents <5% of cases. Several risk factors have been discovered that are associated with AD, with advancing age being the most prominent. Other environmental risk factors include diabetes mellitus, level of physical activity, educational status, hypertension and head injury. The most well known genetic risk factor for LOAD is inheritance of the apolipoprotein (apo) E4 allele. Recently, rare variants of TREM2 have been reported as a significant risk factor for LOAD, comparable to inheritance of apoE4. In this review we will focus on the role(s) of TREM2 in AD as well as in other neurodegenerative disorders.