A Novel PSEN1 M139L Mutation Found in a Chinese Pedigree with Early-Onset Alzheimer's Disease Increases Aβ42/Aβ40 ratio

Genetics, Functions, and Clinical Impact of Presenilin-1 (PSEN1) Gene

Presenilin-1 (PSEN1) has been verified as an important causative factor for early onset Alzheimer's disease (EOAD). PSEN1 is a part of γ-secretase, and in addition to amyloid precursor protein (APP) cleavage, it can also affect other processes, such as Notch signaling, β-cadherin processing, and calcium metabolism. Several motifs and residues have been identified in PSEN1, which may play a significant role in γ-secretase mechanisms, such as the WNF, GxGD, and PALP motifs. More than 300 mutations have been described in PSEN1; however, the clinical phenotypes related to these mutations may be diverse. In addition to classical EOAD, patients with PSEN1 mutations regularly present with atypical phenotypic symptoms, such as spasticity, seizures, and visual impairment. In vivo and in vitro studies were performed to verify the effect of PSEN1 mutations on EOAD. The pathogenic nature of PSEN1 mutations can be categorized according to the ACMG-AMP guidelines; however, some mutations could not be categorized because they were detected only in a single case, and their presence could not be confirmed in family members. Genetic modifiers, therefore, may play a critical role in the age of disease onset and clinical phenotypes of PSEN1 mutations. This review introduces the role of PSEN1 in γ-secretase, the clinical phenotypes related to its mutations, and possible significant residues of the protein.

Microtube Array Membrane Encapsulated Cell Therapy: A Novel Platform Technology Solution for Treatment of Alzheimer's Disease

Alzheimer’s disease is the most frequent form of dementia in aging population and is presently the world’s sixth largest cause of mortality. With the advancement of therapies, several solutions have been developed such as passive immunotherapy against these misfolded proteins, thereby resulting in the clearance. Within this segment, encapsulated cell therapy (ECT) solutions that utilize antibody releasing cells have been proposed with a multitude of techniques under development. Hence, in this study, we utilized our novel and patented Microtube Array Membranes (MTAMs) as an encapsulating platform system with anti-pTau antibody-secreting hybridoma cells to study the impact of it on Alzheimer’s disease. In vivo results revealed that in the water maze, the mice implanted with hybridoma cell MTAMs intracranially (IN) and subcutaneously (SC) showed improvement in the time spent the goal quadrant and escape latency. In passive avoidance, hybridoma cell loaded MTAMs (IN and SC) performed significantly well in step-through latency. At the end of treatment, animals with hybridoma cell loaded MTAMs had lower phosphorylated tau (pTau) expression than empty MTAMs had. Combining both experimental results unveiled that the clearance of phosphorylated tau might rescue the cognitive impairment associated with AD.

The role of genetics in neurodegenerative dementia: a large cohort study in South China

Neurodegenerative dementias are a group of diseases with highly heterogeneous pathology and complicated etiology. There exist potential genetic component overlaps between different neurodegenerative dementias. Here, 1795 patients with neurodegenerative dementias from South China were enrolled, including 1592 with Alzheimer's disease (AD), 110 with frontotemporal dementia (FTD), and 93 with dementia with Lewy bodies (DLB). Genes targeted sequencing analysis were performed. According to the American College of Medical Genetics (ACMG) guidelines, 39 pathogenic/likely pathogenic (P/LP) variants were identified in 47 unrelated patients in 14 different genes, including PSEN1, PSEN2, APP, MAPT, GRN, CHCHD10, TBK1, VCP, HTRA1, OPTN, SQSTM1, SIGMAR1, and abnormal repeat expansions in C9orf72 and HTT. Overall, 33.3% (13/39) of the variants were novel, the identified P/LP variants were seen in 2.2% (35/1592) and 10.9% (12/110) of AD and FTD cases, respectively. The overall molecular diagnostic rate was 2.6%. Among them, PSEN1 was the most frequently mutated gene (46.8%, 22/47), followed by PSEN2 and APP. Additionally, the age at onset of patients with P/LP variants (51.4 years), ranging from 30 to 83 years, was ~10 years earlier than those without P/LP variants (p < 0.05). This study sheds insight into the genetic spectrum and clinical manifestations of neurodegenerative dementias in South China, further expands the existing repertoire of P/LP variants involved in known dementia-associated genes. It provides a new perspective for basic research on genetic pathogenesis and novel guiding for clinical practice of neurodegenerative dementia.

A Rare Variation in the 3' Untranslated Region of the Presenilin 2 Gene Is Linked to Alzheimer's Disease

Rare variations in coding regions may alter the amino acid sequence and function of presenilins (PSENs), which results in the dysfunction of gamma-secretase, in turn contributing to the development of familial Alzheimer's disease (AD). However, whether rare variations in the 3' untranslated region (UTR) may change the expression level of PSEN2 leading to AD remains unclear. In a familial AD pedigree, DNA samples of the patients were screened for APP, PSEN1, and PSEN2 gene mutations using Sanger sequencing. Allele A of rs537889666, a rare variation located in the 3' UTR of PSEN2, was found in all AD patients, but not in the healthy control in the family. Cosegregation analysis (n = 5) revealed that allele A of rs537889666 may be a pathogenic rare variation. The dual-luciferase assay revealed that allele A suppressed the combination of miR-183-5p and the 3' UTR of PSEN2, which may block the miR-183-5p-mediated suppression of PSEN2 expression. Further study showed an elevated ratio of Aβ42/40 under overexpressed PSEN2 conditions. Measurements of the cerebrospinal fluid showed that PSEN2 levels were increased in both sporadic and AD in this family, suggesting that elevated PSEN2 was associated with the disease. In addition, the miR-183-5p inhibitor or mimic can increase or decrease Aβ42/40 ratios. In conclusion, the results indicate that allele A of rs537889666 upregulated PSEN2 levels, increasing the Aβ42/40 ratio and contributing to AD development.

PSEN1, PSEN2, and APP mutations in 404 Chinese pedigrees with familial Alzheimer's disease

INTRODUCTION

The PSENs/APP mutation distribution in Chinese patients with familial Alzheimer's disease (FAD) remains unclear. We aimed to analyze the genetic features of Chinese FAD pedigrees with and without PSENs/APP mutations.

METHODS

In total, 1330 patients with Alzheimer's disease (AD) or mild cognitive impairment in 404 pedigrees were enrolled from the Chinese Familial Alzheimer's Disease Network. PSENs/APP mutations and APOE frequencies were determined.

RESULTS

In total, 13.12% of pedigrees carried PSENs/APP missense mutations, 3.71% carried PSENs/APP synonymous/untranslated region variants, and 83.17% did not carry PSENs/APP mutations. Eleven missense mutations were first identified. In patients without PSENs/APP mutations, 44.31% carried one APOEε4 allele, and 14.85% two APOEε4 alleles.

DISCUSSION

The new PSENs/APP mutations indicate heterogeneity in AD pathogenesis between Chinese and other ethnic groups. The low mutation rate suggests the involvement of other genes/factors in Chinese FAD. APOEε4 might be a major gene for some FAD without PSENs/APP mutations.

Blood neuro-exosomal synaptic proteins predict Alzheimer's disease at the asymptomatic stage

Introduction

Exosomes are an emerging candidate for biomarkers of Alzheimer's disease (AD). This study investigated whether exosomal synaptic proteins can predict AD at the asymptomatic stage.

Methods

We conducted a two‐stage‐sectional study (discovery stage: AD, 28; amnestic mild cognitive impairment [aMCI], 25; controls, 29; validation stage: AD, 73; aMCI, 71; controls, 72), a study including preclinical AD (160) and controls (160), and a confirmation study in familial AD (mutation carriers: 59; non‐mutation carriers: 62).

Results

The concentrations of growth associated protein 43 (GAP43), neurogranin, synaptosome associated protein 25 (SNAP25), and synaptotagmin 1 were lower in AD than in controls (P < .001). Exosomal biomarker levels were correlated with those in cerebrospinal fluid (R² = 0.54–0.70). The combination of exosomal biomarkers detected AD 5 to 7 years before cognitive impairment (area under the curve = 0.87–0.89).

Discussion

This study revealed that exosomal GAP43, neurogranin, SNAP25, and synaptotagmin 1 act as effective biomarkers for prediction of AD 5 to 7 years before cognitive impairment.

Gene mutations associated with early onset familial Alzheimer's disease in China: An overview and current status

BACKGROUND

Mutations of three causative genes, namely presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP), have been identified as the major causes of early-onset familial Alzheimer's disease (EOFAD). The prevalence of causative gene mutations in patients with EOFAD has been reported in previous studies worldwide but remains unclear in China. The patients with these known mutations always show considerable clinical phenotypic variability. However, to date, there have been no detailed descriptions of the clinical phenotypes associated with these Chinese EOFAD mutations. Thus, the aim of this study was to describe all of the known mutations in three EOFAD causative genes and genotype-phenotype correlations in Chinese patients with EOFAD.

METHOD

We systematically searched the PubMed, MEDLINE, CNKI, VIP, and WAN-FANG databases to find Chinese EOFAD mutations in reports from inception through May 2020.

RESULT

We identified 31 studies reporting mutations of three causative genes in China. 10 mutations in APP gene, 27 mutations in PSEN1 gene and six mutations in PSEN2 were discovered in Chinese EOFAD. This review summarized all these probably pathogenic mutations as well as its clinical features. To the best of our knowledge, this is the first systemic review of causative gene mutations in patients with EOFAD in China.

CONCLUSION

The analysis of the genetic and clinical phenotype correlations in this review supports the idea that the clinical phenotype might be influenced by specific genetic defects. It also suggests genetic testing and genotype-phenotype correlations are important for the accurate diagnosis and for understanding disease-associated pathways and might also improve disease therapy and prevention.

The Genetics of Alzheimer's Disease in the Chinese Population

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by progressive cognitive dysfunction and behavioral impairment. In China, the number of AD patients is growing rapidly, which poses a considerable burden on society and families. In recent years, through the advancement of genome-wide association studies, second-generation gene sequencing technology, and their application in AD genetic research, more genetic loci associated with the risk for AD have been discovered, including KCNJ15, TREM2, and GCH1, which provides new ideas for the etiology and treatment of AD. This review summarizes three early-onset AD causative genes (APP, PSEN1, and PSEN2) and some late-onset AD susceptibility genes and their mutation sites newly discovered in China, and briefly introduces the potential mechanisms of these genetic susceptibilities in the pathogenesis of AD, which would help in understanding the genetic mechanisms underlying this devastating disease.

Is Alzheimer's Disease a Liver Disease of the Brain?

Clinical specialization is not only a force for progress, but it has also led to the fragmentation of medical knowledge. The focus of research in the field of Alzheimer's disease (AD) is neurobiology, while hepatologists focus on liver diseases and lipid specialists on atherosclerosis. This article on AD focuses on the role of the liver and lipid homeostasis in the development of AD. Amyloid-β (Aβ) deposits accumulate as plaques in the brain of an AD patient long before cognitive decline is evident. Aβ generation is a normal physiological process; the steady-state level of Aβ in the brain is determined by balance between Aβ production and its clearance. We present evidence suggesting that the liver is the origin of brain Aβ deposits and that it is involved in peripheral clearance of circulating Aβ in the blood. Hence the liver could be targeted to decrease Aβ production or increase peripheral clearance.