A novel presenilin 1 mutation (Leu166Arg) associated with early-onset Alzheimer disease

Genetic landscape of early-onset dementia in Hungary

Introduction

Early-onset dementias (EOD) are predominantly genetically determined, but the underlying disease-causing alterations are often unknown. The most frequent forms of EODs are early-onset Alzheimer’s disease (EOAD) and frontotemporal dementia (FTD).

Patients

This study included 120 Hungarian patients with EOD (48 familial and 72 sporadic) which had a diagnosis of EOAD (n = 49), FTD (n = 49), or atypical dementia (n = 22).

Results

Monogenic dementia was detected in 15.8% of the patients. A pathogenic hexanucleotide repeat expansion in the C9ORF72 gene was present in 6.7% of cases and disease-causing variants were detected in other known AD or FTD genes in 6.7% of cases (APP, PSEN1, PSEN2, GRN). A compound heterozygous alteration of the TREM2 gene was identified in one patient and heterozygous damaging variants in the CSF1R and PRNP genes were detected in two other cases. In two patients, the coexistence of several heterozygous damaging rare variants associated with neurodegeneration was detected (1.7%). The APOE genotype had a high odds ratio for both the APOE ɛ4/3 and the ɛ4/4 genotype (OR = 2.7 (95%CI = 1.3–5.9) and OR = 6.5 (95%CI = 1.4–29.2), respectively). In TREM2, SORL1, and ABCA7 genes, 5 different rare damaging variants were detected as genetic risk factors. These alterations were not present in the control group.

Conclusion

Based on our observations, a comprehensive, targeted panel of next-generation sequencing (NGS) testing investigating several neurodegeneration-associated genes may accelerate the path to achieve the proper genetic diagnosis since phenotypes are present on a spectrum. This can also reveal hidden correlations and overlaps in neurodegenerative diseases that would remain concealed in separated genetic testing.

A pathogenic PSEN1 Trp165Cys mutation associated with early-onset Alzheimer's disease

Background

Presenilin-1 (PSEN1) is one of the causative genes for early onset Alzheimer’s disease (EOAD). Recently, emerging studies reported several novel PSEN1 mutations among Asian. We describe a male with EOAD had a pathogenic PSEN1 mutation.

Case presentation

A 53-year-old male presented with memory decline, followed by difficulty in finding ways. Patient had positive family history, since his mother and one of his brother was also affected with dementia. Brain magnetic resonance imaging (MRI) scan showed mild degree of atrophy of bilateral hippocampus and parietal lobe. ¹⁸F-Florbetaben-PET (FBB-PET) revealed increased amyloid deposition in bilateral frontal, parietal, temporal lobe and precuneus. Whole exome analysis revealed a heterozygous, probably pathogenic PSEN1 (c.695G > T, p.W165C) mutation. Interestingly, Trp165Cys mutation is located in trans membrane (TM)-III region, which is conserved between PSEN1/PSEN2. In vitro studies revealed that PSEN1 Trp165Cys could result in disturbances in amyloid metabolism. This prediction was confirmed by structure predictions and previous in vitro studies that the p.Trp165Cys could result in decreased Aβ42/Aβ40 ratios.

Conclusion

We report a case of EOAD having a pathogenic PSEN1 (Trp165Cys) confirmed with in silico and in vitro predictions.

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.

Exome sequencing identifies 2 novel presenilin 1 mutations (p.L166V and p.S230R) in British early-onset Alzheimer's disease

Early-onset Alzheimer's disease (EOAD) represents 1%–2% of the Alzheimer's disease (AD) cases, and it is generally characterized by a positive family history and a rapidly progressive symptomatology. Rare coding and fully penetrant variants in amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) are the only causative mutations reported for autosomal dominant AD. Thus, in this study we used exome sequencing data to rapidly screen rare coding variability in APP, PSEN1, and PSEN2, in a British cohort composed of 47 unrelated EOAD cases and 179 elderly controls, neuropathologically proven. We report 2 novel and likely pathogenic variants in PSEN1 (p.L166V and p.S230R). A comprehensive catalog of rare pathogenic variants in the AD Mendelian genes is pivotal for a premortem diagnosis of autosomal dominant EOAD and for the differential diagnosis with other early onset dementias such as frontotemporal dementia (FTD) and Creutzfeldt-Jakob disease (CJD).

Previously not recognized deletion in presenilin-1 (p.Leu174del.) in a patient with early-onset familial Alzheimer's disease

We report on a previously not recognized mutation in exon 6 of presenilin-1 (PSEN1) (c.520_522delCTG) in a male patient with early onset familial Alzheimer disease. The mutation results in the deletion of a leucine at amino acid position 174 of the protein. The index patient presented with progressive memory loss at 50 years of age. Initially, depression was the only ancillary symptom. At age 53 clinical diagnosis of early Alzheimer disease was made based on neuropsychological, neuroimaging, and CSF findings. The patient's father and his paternal grandmother also suffered from memory loss and cognitive decline. The clinical findings in the patient are similar to signs and symptoms in previously reported patients with missense mutations at codon 174 of PSEN1.

The Genetics of Very Early Onset Alzheimer Disease

OBJECTIVE

This study was undertaken to clarify the genetics of very early onset Alzheimer disease (VEOAD), defined as AD beginning before age 35.

BACKGROUND

Early onset AD (EOAD) is defined by onset of symptoms before age 65, and affected individuals may harbor a mutation in presenilin 1 (PSEN1), presenilin 2 (PSEN2), or amyloid precursor protein. VEOAD is exceedingly rare, and PSEN1 mutations have been implicated. We encountered a man with phenotypic frontotemporal dementia beginning at age 32 and a strong family history of an autosomal dominant dementia who was found at autopsy to have AD.

METHODS

Histologic and genetic analyses of the patient's brain were undertaken, and a review of all published VEOAD cases was performed.

RESULTS

Histologic findings were diagnostic of advanced stage AD. Genetic evaluation of brain tissue identified an intronic PSEN1 polymorphism; no known pathogenic mutation was found. Literature review (1934 to 2007) disclosed 101 cases of VEOAD; the youngest age of dementia onset was 24 years. In all cases in which definitive genetic analysis was available, either a PSEN1 mutation or linkage to chromosome 14 was found.

CONCLUSIONS

VEOAD can present with atypical clinical features, including findings suggestive of frontotemporal dementia. All reported cases of VEOAD with conclusive genetic analysis seem to be associated with PSEN1 mutations. Genetic testing in adults younger than 35 with dementia can identify the genetic defect and assist in diagnosis and family counseling.

A novel presenilin 1 deletion (p.L166del) associated with early onset familial Alzheimer's disease

We report the case of a 40 year-old woman who, at 38 years of age, developed insidious memory loss and, subsequently, progressive dementia satisfying criteria for probable Alzheimer's disease (AD) (NINCDS-ADRDA) [Neurology 1984; 34: 939]. Analysis of the presenilin 1 gene (PSEN1) revealed a 496_498delCTT mutation at codon 166. The amnestic presentation and absence of other features contrasts with the majority of other documented deletions which have been associated with spastic paraparesis. They are, however, consistent with the reported clinical phenotype in the majority of PSEN1 exon 6 mutations so far reported.

Abeta42-driven cerebral amyloidosis in transgenic mice reveals early and robust pathology

We have generated a novel transgenic mouse model on a C57BL/6J genetic background that coexpresses KM670/671NL mutated amyloid precursor protein and L166P mutated presenilin 1 under the control of a neuron-specific Thy1 promoter element (APPPS1 mice). Cerebral amyloidosis starts at 6-8 weeks and the ratio of human amyloid (A)beta42 to Abeta40 is 1.5 and 5 in pre-depositing and amyloid-depositing mice, respectively. Consistent with this ratio, extensive congophilic parenchymal amyloid but minimal amyloid angiopathy is observed. Amyloid-associated pathologies include dystrophic synaptic boutons, hyperphosphorylated tau-positive neuritic structures and robust gliosis, with neocortical microglia number increasing threefold from 1 to 8 months of age. Global neocortical neuron loss is not apparent up to 8 months of age, but local neuron loss in the dentate gyrus is observed. Because of the early onset of amyloid lesions, the defined genetic background of the model and the facile breeding characteristics, APPPS1 mice are well suited for studying therapeutic strategies and the pathomechanism of amyloidosis by cross-breeding to other genetically engineered mouse models.

Genetics, transcriptomics, and proteomics of Alzheimer's disease

OBJECTIVE

To provide an updated overview of the methods used in genetic, transcriptomic, and proteomic studies in Alzheimer's disease and to demonstrate the importance of those methods for the improvement of the current diagnostic and therapeutic possibilities.

DATA SOURCES

MEDLINE-based search of 233 peer-reviewed articles published between 1975 and 2006.

DATA SYNTHESIS

Alzheimer's disease is a genetically heterogeneous disorder. Rare mutations in the amyloid precursor protein, presenilin 1, and presenilin 2 genes have shown the importance of the amyloid metabolism for its development. In addition, converging evidence from population-based genetic studies, gene expression studies, and protein profile studies in the brain and in the cerebrospinal fluid suggest the existence of several pathogenetic pathways such as amyloid precursor protein processing, beta-amyloid degradation, tau phosphorylation, proteolysis, protein misfolding, neuroinflammation, oxidative stress, and lipid metabolism.

CONCLUSIONS

The development of high-throughput genotyping methods and of elaborated statistical analyses will contribute to the identification of genetic risk profiles related to the development and course of this devastating disease. The integration of knowledge derived from genetic, transcriptomic, and proteomic studies will greatly advance our understanding of the causes of Alzheimer's disease, improve our capability of establishing an early diagnosis, help define disease subgroups, and ultimately help to pave the road toward improved and tailored treatments.

Clinical phenotypic heterogeneity of Alzheimer's disease associated with mutations of the presenilin-1 gene

It is now 10 years since the first report of mutations in the presenilin genes that were deterministic for familial autosomal dominant Alzheimer's disease. The most common of these mutations occurs in the presenilin-1 gene (PSEN1) located on chromosome 14. In the ensuing decade, more than 100 PSEN1 mutations have been described. The emphasis of these reports has largely been on the novelty of the mutations and their potential pathogenic consequences rather than detailed clinical, neuropsychological, neuroimaging and neuropathological accounts of patients with the mutation. This article reviews the clinical phenotypes of reported PSEN1 mutations, emphasizing their heterogeneity, and suggesting that other factors, both genetic and epigenetic,must contribute to disease phenotype.

Clinical, pathological, and biochemical spectrum of Alzheimer disease associated with PS-1 mutations

Three genes have been implicated in the etiology of early-onset autosomal-dominant Alzheimer disease (AD): the amyloid precursor protein, the presenilin-1, and presenilin-2 genes. Approximately half of autosomal-dominant AD cases are associated with mutations in the presenilin-1 (PS-1) gene on the long arm of Chromosome 14. Marked allelic heterogeneity characterizes families with PS-1 gene mutations; more than 100 different mutations have been found in independent families thus far. With the exception of age at onset, the clinical phenotype is similar to late-onset AD, although some rare specific phenotypes have been described. These mutations lead to enhanced deposition of total Abeta and Abeta42 (but not Abeta40) in the brain, compared with sporadic AD. There is a considerable heterogeneity in the histological profiles among brains from patients with different mutations, and although some lead to predominantly parenchymal deposition of Abeta in the form of diffuse and cored plaques, others show predominantly vascular deposition, with severe amyloid angiopathy. Only some mutations are associated with enhanced neurofibrillary tangle formation and increased neuronal loss compared with sporadic AD. However, there is an important clinical and pathological variability even among family members with the same mutation, which suggests the involvement of other genetic or environmental factors that modulate the clinical expression of the disease. This represents a valuable model for identifying such factors and has potential implications for the development of new therapeutic strategies for delaying disease onset.

Presenilin-1 mutations of leucine 166 equally affect the generation of the Notch and APP intracellular domains independent of their effect on Abeta 42 production

The Alzheimer's disease (AD)-associated presenilin (PS) proteins are required for the gamma-secretase cleavages of the beta-amyloid precursor protein and the site 3 (S3) protease cleavage of Notch. These intramembrane cleavages release amyloid-beta peptide (Abeta), including the pathogenic 42-aa variant (Abeta(42)), as well as the beta-amyloid precursor protein and the Notch intracellular domains (AICD, NICD). Whereas Abeta is generated by endoproteolysis in the middle of the transmembrane domain, AICD and NICD are generated by cleavages at analogous positions close to the cytoplasmic border of the transmembrane domain. Numerous mutations causing familial AD (FAD) that all cause increased production of Abeta(42) have been found in the PS1 gene. Here we have investigated the previously uncharacterized, very aggressive FAD mutation L166P that causes onset of AD in adolescence. Strikingly, the PS1 L166P mutation not only induces an exceptionally high increase of Abeta(42) production but also impairs NICD production and Notch signaling, as well as AICD generation. Thus, FAD-associated PS mutants cannot only affect the generation of NICD, but also that of AICD. Moreover, further analysis with artificial L166 mutants revealed that the gamma-secretase cleavage at position 40/42 and the S3-like gamma-secretase cleavage at position 49 of the Abeta domain are both differentially affected by PS1 L166 mutants. Finally, we show that PS1 L166 mutants affect the generation of NICD and AICD in a similar manner, supporting the concept that S3 protease and S3-like gamma-secretase cleavages are mediated by identical proteolytic activities.