A novel presenilin 1 mutation (Ala275Val) as cause of early-onset familial Alzheimer disease

Discovery and validation of dominantly inherited Alzheimer’s disease mutations in populations from Latin America

Background

In fewer than 1% of patients, AD is caused by autosomal dominant mutations in either the presenilin 1 (PSEN1), presenilin 2 (PSEN2), or amyloid precursor protein (APP) genes. The full extent of familial AD and frequency of these variants remains understudied in Latin American (LatAm) countries. Due to the rare nature of these variants, determining the pathogenicity of a novel variant in these genes can be challenging. Here, we use a systematic approach to assign the likelihood of pathogenicity in variants from densely affected families in Latin American populations.

Methods

Clinical data was collected from LatAm families at risk for DIAD. Symptomatic family members were identified and assessed by local clinicians and referred for genetic counseling and testing. To determine the likelihood of pathogenicity among variants of unknown significance from LatAm populations, we report pedigree information, frequency in control populations, in silico predictions, and cell-based models of amyloid-beta ratios.

Results

We identified five novel variants in the presenilin1 (PSEN1) gene from Brazilian and Mexican families. The mean age at onset in newly identified families was 43.5 years (range 36–54). PSEN1 p.Val103_Ser104delinsGly, p.Lys395Ile, p.Pro264Se, p.Ala275Thr, and p.Ile414Thr variants have not been reported in PubMed, ClinVar, and have not been reported in dominantly inherited AD (DIAD) families. We found that PSEN1 p.Val103_Ser104delinsGly, p.Lys395Ile, p.Pro264Se, and p.Ala275Thr produce Aβ profiles consistent with known AD pathogenic mutations. PSEN1 p.Ile414Thr did not alter Aβ in a manner consistent with a known pathogenic mutation.

Conclusions

Our study provides further insights into the genetics of AD in LatAm. Based on our findings, including clinical presentation, imaging, genetic, segregations studies, and cell-based analysis, we propose that PSEN1 p.Val103_Ser104delinsGly, p.Lys395Ile, p.Pro264Se, and p.Ala275Thr are likely pathogenic variants resulting in DIAD, whereas PSEN1 p.Ile414Thr is likely a risk factor. This report is a step forward to improving the inclusion/engagement of LatAm families in research. Family discovery is of great relevance for the region, as new initiatives are underway to extend clinical trials and observational studies to families living with DIAD.

Novel Presenilin-1 Mutation (Ala275Ser) Associated With Clinical Features of Dementia With Lewy Bodies

We report a case of familial dementia having some clinical features characteristic of dementia with Lewy bodies, in which a novel mutation Ala275Ser within the presenilin-1 (PSEN1) gene was identified. We review the association of PSEN1 mutation with dementia with Lewy bodies features, noting this to be an uncommonly reported observation.

Presenilin-1 mutation is associated with a hippocampus defect in alzheimer's disease: Meta-Analysis for neuroimaging research

Observational studies suggested an association of the Presenilin-1 (PSEN1) genotype with neuroimaging markers within Alzheimer's disease. However, whether the PSEN1 genotype and neuroimaging markers is a harbinger of Alzheimer's disease remains controversial. We aimed to examine the association of the PSEN1 mutation with neuroimaging markers in Alzheimer's disease: hippocampal volume, cerebral metabolism and brain amyloid deposition. We performed a systematic review and meta-analysis of 13 studies identified in Pubmed and Medline from 1997 to 2019 (n = 164). The pooled standard mean difference (SMD) was used to evaluate the association between the PSEN1 mutation and hippocampal volume and cerebral metabolism rate for glucose (CMRgl). A meta-analysis was also performed regarding the amyloid deposition between the PSEN1+ and PSEN1- groups. In order to accurately study whether PSEN1 independently was associated with changes in related image markers, sub-meta analyses was performed. The PSEN1 mutation was associated with a smaller hippocampal volume (pooled SMD: -3.3; 95 % CI: -5.36 to -1.24; p = 0.002) and decreased cerebral metabolism (pooled SMD: -1.73; 95 % CI: -2.7 to -0.76; p < 0.0001). Additionally, PSEN1 was associated with increased cerebral amyloid deposition as detected by a positron emission tomography tracer (pooled SMD: 4.58; 95 % CI: 1.37-7.8; p = 0.0005). PSEN1 was associated with a decreased hippocampal volume in MRI markers, cerebral glucose hypometabolism, and increased cerebral amyloid deposition. These associations may indicate the potential role of neuroimaging markers for the diagnosis of Alzheimer's disease.

Genetic Markers of Alzheimer's Disease

Alzheimer's disease is a complex and heterogeneous, severe neurodegenerative disorder and the predominant form of dementia, characterized by cognitive disturbances, behavioral and psychotic symptoms, progressive cognitive decline, disorientation, behavioral changes, and death. Genetic background of Alzheimer's disease differs between early-onset familial Alzheimer's disease, other cases of early-onset Alzheimer's disease, and late-onset Alzheimer's disease. Rare cases of early-onset familial Alzheimer's diseases are caused by high-penetrant mutations in genes coding for amyloid precursor protein, presenilin 1, and presenilin 2. Late-onset Alzheimer's disease is multifactorial and associated with many different genetic risk loci (>20), with the apolipoprotein E ε4 allele being a major genetic risk factor for late-onset Alzheimer's disease. Genetic and genomic studies offer insight into many additional genetic risk loci involved in the genetically complex nature of late-onset Alzheimer's disease. This review highlights the contributions of individual loci to the pathogenesis of Alzheimer's disease and suggests that their exact contribution is still not clear. Therefore, the use of genetic markers of Alzheimer's disease, for monitoring development, time course, treatment response, and prognosis of Alzheimer's disease, is still far away from the clinical application, because the contribution of genetic variations to the relative risk of developing Alzheimer's disease is limited. In the light of prediction and prevention of Alzheimer's disease, a novel approach could be found in the form of additive genetic risk scores, which combine additive effects of numerous susceptibility loci.

A Novel PSEN1 K311R Mutation Discovered in Chinese Families with Late-Onset Alzheimer's Disease Affects Amyloid-β Production and Tau Phosphorylation

BACKGROUND

Presenilin-1 (PSEN1) is the most frequently mutated gene in familial Alzheimer's disease (AD), whereas only several novel mutations have been reported in China and functional studies were seldom conducted.

OBJECTIVE

We describe a novel PSEN1 K311R mutation in two Chinese families with late-onset AD and its functional impact on amyloid-β protein precursor (AβPP) processing and tau phosphorylation.

METHODS

The mutation was detected by direct sequencing of PSEN1 exon 9. HEK293 cells stably expressing wild-type APP695 (HEK293-APP695wt) were transfected with plasmids containing human wild-type PSEN1, PSEN1 K311R mutation, and PSEN1 E280A mutation to compare the K311R mutation's effects on AβPP processing with other groups. In addition, each group of cells were co-transfected with plasmids harboring PSEN1 and human wild-type MAPT complementary DNA to study the mutation's impacts on tau phosphorylation.

RESULTS

The K311R mutation was detected in probands of two late-onset AD families. Expression of the K311R or E280A mutation increased amyloid-β (Aβ)42 levels but decreased Aβ40 levels, resulting in an overall increase in the Aβ42/Aβ40 ratio compared to those in wild-type PSEN1 transfected cells (p < 0.05). The K311R or E280A mutation also increased the levels of phosphorylated tau compared to wild-type PSEN1 (p < 0.05).

CONCLUSION

The K311R mutation might contribute to AD pathogenesis by overproducing toxic Aβ species and enhancing tau phosphorylation. Further in-depth studies are needed to decipher the pathogenic mechanisms of the K311R mutation in terms of AβPP cleavage, tau phosphorylation, and other presenilin-1 mediated functional pathways.

Cerebrospinal Fluid Biomarkers in Familial Forms of Alzheimer's Disease and Frontotemporal Dementia

As dementia is a fast-growing health care problem, it is becoming an increasingly urgent need to provide an early diagnosis in order to offer patients the best medical treatment and care. Validated biomarkers which reflect the pathology and disease progression are essential for diagnosis and are important when developing new therapies. Today, the core protein biomarkers amyloid-β42, total tau and phosphorylated tau in the cerebrospinal fluid (CSF) are used to diagnose Alzheimer's disease (AD), because these biomarkers have shown to reflect the underlying amyloid and tau pathology. However, the biomarkers have proved insufficient predictors of dementias with a different pathology, e.g. frontotemporal dementia (FTD); furthermore, the biomarkers are not useful for early AD diagnosis. Familial dementias with a known disease-causing mutation can be extremely valuable to study; yet the biomarker profiles in patients with familial dementias are not clear. This review summarizes CSF biomarker findings from studies on symptomatic and presymptomatic individuals carrying a mutation in one of the genes known to cause early-onset familial AD or FTD. In conclusion, the biomarker profile of inherited AD is quite similar between carriers of different mutations as well as similar to the profile found in sporadic AD, whereas familial FTD does not seem to have a clear biomarker profile. Hence, new biomarkers are needed for FTD.