Familial Alzheimer's disease genes in Japanese

PRESENILIN 1 Mutations Causing Early-Onset Familial Alzheimer's Disease or Familial Acne Inversa Differ in Their Effects on Genes Facilitating Energy Metabolism and Signal Transduction

BACKGROUND

The most common cause of early-onset familial Alzheimer's disease (EOfAD) is mutations in PRESENILIN 1 (PSEN1) allowing production of mRNAs encoding full-length, but mutant, proteins. In contrast, a single known frameshift mutation in PSEN1 causes familial acne inversa (fAI) without EOfAD. The molecular consequences of heterozygosity for these mutation types, and how they cause completely different diseases, remains largely unexplored.

OBJECTIVE

To analyze brain transcriptomes of young adult zebrafish to identify similarities and differences in the effects of heterozygosity for psen1 mutations causing EOfAD or fAI.

METHODS

RNA sequencing was performed on mRNA isolated from the brains of a single family of 6-month-old zebrafish siblings either wild type or possessing a single, heterozygous EOfAD-like or fAI-like mutation in their endogenous psen1 gene.

RESULTS

Both mutations downregulate genes encoding ribosomal subunits, and upregulate genes involved in inflammation. Genes involved in energy metabolism appeared significantly affected only by the EOfAD-like mutation, while genes involved in Notch, Wnt and neurotrophin signaling pathways appeared significantly affected only by the fAI-like mutation. However, investigation of direct transcriptional targets of Notch signaling revealed possible increases in γ-secretase activity due to heterozygosity for either psen1 mutation. Transcriptional adaptation due to the fAI-like frameshift mutation was evident.

CONCLUSION

We observed both similar and contrasting effects on brain transcriptomes of the heterozygous EOfAD-like and fAI-like mutations. The contrasting effects may illuminate how these mutation types cause distinct diseases.

APP, PSEN1, and PSEN2 Mutations in Asian Patients with Early-Onset Alzheimer Disease

The number of patients with Alzheimer's disease (AD) is rapidly increasing in Asia. Mutations in the amyloid protein precursor (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2) genes can cause autosomal dominant forms of early-onset AD (EOAD). Although these genes have been extensively studied, variant classification remains a challenge, highlighting the need to colligate mutations across populations. In this study, we performed a genetic screening for mutations in the APP, PSEN1, and PSEN2 genes in 200 clinically diagnosed EOAD patients across four Asian countries, including Thailand, Malaysia, the Philippines, and Korea, between 2009 and 2018. Thirty-two (16%) patients presented pathogenic APP, PSEN1, or PSEN2 variants; eight (25%), 19 (59%), and five (16%) of the 32 patients presented APP, PSEN1, and PSEN2 variants, respectively. Among the 21 novel and known non-synonymous variants, five APP variants were found in Korean patients and one APP variant was identified in a Thai patient with EOAD. Nine, two, and one PSEN1 mutation was found in a Korean patient, Malaysian siblings, and a Thai patient, respectively. Unlike PSEN1 mutations, PSEN2 mutations were rare in patients with EOAD; only three variants were found in Korean patients with EOAD. Comparison of AD-causative point mutations in Asian countries; our findings explained only a small fraction of patients, leaving approximately 84% (p = 0.01) of autosomal dominant pedigrees genetically unexplained. We suggest that the use of high-throughput sequencing technologies for EOAD patients can potentially improve our understanding of the molecular mechanisms of AD.

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.

PSEN1 p.Thr116Ile Variant in Two Korean Families with Young Onset Alzheimer's Disease

An in depth study of PSEN1 mutation p.Thr116Ile (c.335C>T) is presented from two Korean families with autosomal dominant inheritance. Clinical manifestation of our patients included memory loss, attention deficits, visuospatial dysfunction, agnosia, aphasia, apraxia, and personality changes, which occurred in their 30s. PSEN1 Thr116Ile was initially discovered in an Italian patient and two French families with early onset Alzheimer’s disease (EOAD) with similar age of onset. To verify the possible pathogenic mechanisms of mutation, in silico predictions and 3D modeling were performed. Structure predictions revealed significant aberrations in first hydrophilic loop (HL-I loop). The hydrophobic isoleucine could alter the loop orientation through increased hydrophobic contacts with the surrounding amino acids. Mutation could destroy a possible hydrogen bond between tyrosine 115 and threonine 116, which may affect the loop conformation. HL-I was confirmed as a conservative region of PSEN1, which may be critical in PSEN1 functions. An additional pathogenic mutation, PSEN1 Thr116Asn, was also found for the same residue, where the patient presented young onset AD (YOND). Other mutations in HL-I loop, such as Tyr115His and Glu120Asp, were described in patients with YOND, supporting the critical role of HL-I loop in PSEN1 activity.

Identification of missing variants by combining multiple analytic pipelines

Background

After decades of identifying risk factors using array-based genome-wide association studies (GWAS), genetic research of complex diseases has shifted to sequencing-based rare variants discovery. This requires large sample sizes for statistical power and has brought up questions about whether the current variant calling practices are adequate for large cohorts. It is well-known that there are discrepancies between variants called by different pipelines, and that using a single pipeline always misses true variants exclusively identifiable by other pipelines. Nonetheless, it is common practice today to call variants by one pipeline due to computational cost and assume that false negative calls are a small percent of total.

Results

We analyzed 10,000 exomes from the Alzheimer’s Disease Sequencing Project (ADSP) using multiple analytic pipelines consisting of different read aligners and variant calling strategies. We compared variants identified by using two aligners in 50,100, 200, 500, 1000, and 1952 samples; and compared variants identified by adding single-sample genotyping to the default multi-sample joint genotyping in 50,100, 500, 2000, 5000 and 10,000 samples. We found that using a single pipeline missed increasing numbers of high-quality variants correlated with sample sizes. By combining two read aligners and two variant calling strategies, we rescued 30% of pass-QC variants at sample size of 2000, and 56% at 10,000 samples. The rescued variants had higher proportions of low frequency (minor allele frequency [MAF] 1–5%) and rare (MAF < 1%) variants, which are the very type of variants of interest. In 660 Alzheimer’s disease cases with earlier onset ages of ≤65, 4 out of 13 (31%) previously-published rare pathogenic and protective mutations in APP, PSEN1, and PSEN2 genes were undetected by the default one-pipeline approach but recovered by the multi-pipeline approach.

Conclusions

Identification of the complete variant set from sequencing data is the prerequisite of genetic association analyses. The current analytic practice of calling genetic variants from sequencing data using a single bioinformatics pipeline is no longer adequate with the increasingly large projects. The number and percentage of quality variants that passed quality filters but are missed by the one-pipeline approach rapidly increased with sample size.

Electronic supplementary material

The online version of this article (10.1186/s12859-018-2151-0) contains supplementary material, which is available to authorized users.

A case of possibly pathogenic PSEN2 R62C mutation in a patient with probable early-onset Alzheimer's dementia supported by structure prediction

A 49-year-old Korean male patient with dementia was diagnosed with probable early-onset Alzheimer’s disease (AD). He presented with memory problems, personality changes, and disorientation. His family history of dementia was probably negative, since no family member with dementia was found or mentioned. Mild cortical atrophy was observed upon magnetic resonance imaging analyses of his brain, and the single-photon emission computed tomography analysis revealed hypoperfusion in the frontal, temporal, and limbic lobes. The patient was tested for mutations in APP, PSEN1, PSEN2, PGRN, MAPT, and PRNP genes. Genetic analysis revealed R62C mutation in PSEN2 gene. PSEN2 R62C mutation was previously reported in European populations, including Dutch and Belgian families with AD. Herein, we present the first case report of PSEN2 R62C mutation in Asia. PolyPhen-2 and SIFT software analyses predicted this mutation as “possibly damaging”, suggesting its potential involvement with AD. In silico protein structural prediction analyses of PSEN2 R62 and C62 revealed two divergent structures, suggesting that large perturbations of R62C mutation might cause dysfunctions of PSEN2, which may alter the normal amyloid production.

Analysis of 138 pathogenic mutations in presenilin-1 on the in vitro production of Aβ42 and Aβ40 peptides by γ-secretase

A hallmark of Alzheimer's disease (AD) is the aggregation of β-amyloid peptides (Aβ) into amyloid plaques in patient brain. Cleavage of amyloid precursor protein (APP) by the intramembrane protease γ-secretase produces Aβ of varying lengths, of which longer peptides such as Aβ42 are thought to be more harmful. Increased ratios of longer Aβs over shorter ones, exemplified by the ratio of Aβ42 over Aβ40, may lead to formation of amyloid plaques and consequent development of AD. In this study, we analyzed 138 reported mutations in human presenilin-1 (PS1) by individually reconstituting the mutant PS1 proteins into anterior-pharynx-defective protein 1 (APH-1)aL-containing γ-secretases and examining their abilities to produce Aβ42 and Aβ40 in vitro. About 90% of these mutations lead to reduced production of Aβ42 and Aβ40. Notably, 10% of these mutations result in decreased Aβ42/Aβ40 ratios. There is no statistically significant correlation between the Aβ42/Aβ40 ratio produced by a γ-secretase variant containing a specific PS1 mutation and the mean age at onset of patients from whom the mutation was isolated.

Mutations, associated with early-onset Alzheimer's disease, discovered in Asian countries

Alzheimer's disease (AD), the most common form of senile dementia, is a genetically complex disorder. In most Asian countries, the population and the number of AD patients are growing rapidly, and the genetics of AD has been extensively studied, except in Japan. However, recent studies have been started to investigate the genes and mutations associated with AD in Korea, the People's Republic of China, and Malaysia. This review describes all of the known mutations in three early-onset AD (EOAD) causative genes (APP, PSEN1, and PSEN2) that were discovered in Asian countries. Most of the EOAD-associated mutations have been detected in PSEN1, and several novel PSEN1 mutations were recently identified in patients from various parts of the world, including Asia. Until 2014, no PSEN2 mutations were found in Asian patients; however, emerging studies from Korea and the People's Republic of China discovered probably pathogenic PSEN2 mutations. Since several novel mutations were discovered in these three genes, we also discuss the predictions on their pathogenic nature. This review briefly summarizes genome-wide association studies of late-onset AD and the genes that might be associated with AD in Asian countries. Standard sequencing is a widely used method, but it has limitations in terms of time, cost, and efficacy. Next-generation sequencing strategies could facilitate genetic analysis and association studies. Genetic testing is important for the accurate diagnosis and for understanding disease-associated pathways and might also improve disease therapy and prevention.

PSEN1 L226F mutation in a patient with early-onset Alzheimer's disease in Korea

In this study, we report a first 226leucine (Leu) mutation to phenylalanine (Phe) in (PSEN1, CTC>TTC, L226F) in Asia from a Korean early-onset Alzheimer's disease (EOAD) patient. Polymerase chain reaction (PCR)-single strand conformation polymorphism, sequencing, and in silico predictions were performed. Previously, L226F was reported in EOAD patients by Zekanowski et al and Gómez-Tortosa et al. Disease phenotypes appeared in their thirties, and family history was positive in both cases. In our patient, age of onset was similar (37 years of age), but the mutation seemed to be de novo, since no affected family member was found. This leucine to phenylalanine substitution may cause additional stresses inside the transmembrane region due to large aromatic side chain and increased hydrophobic interactions with hydrocarbon chains in the membrane and its binding partners. Clinical phenotype of the mutation was aggressive progression into neurodegeneration, resulting in rapid cognitive decline. One of the patients was initially diagnosed with frontotemporal dementia, but the diagnosis was revised to AD upon postmortem studies in which Aβ plaques were seen. A second mutation, L226R, was found for the L226 residue. Similar to L226F, the patient with L226R also developed the first symptoms in his 30s, but EOAD was diagnosed in his 40s. These findings suggested that L226 might be an important residue in PSEN1, since mutations could result in neurodegenerative disease phenotypes at relatively young ages. There are mutations, such as L226F, which may not present clear clinical symptoms for the definitive diagnosis between frontotemporal dementia and AD. In addition, the similarities in the phenotypes could also be possible between AD and frontotemporal dementia, suggesting difficulties in differential diagnosis of various neurodegenerative diseases.

Novel PSEN1 G209A mutation in early-onset Alzheimer dementia supported by structural prediction

Background

Three main genes are described as causative genes for early-onset Alzheimer dementia (EOAD): APP, PSEN1 and PSEN2. We describe a woman with EOAD had a novel PSEN1 mutation.

Case report

A 54-year-old right-handed woman presented 12-year history of progressive memory decline. She was clinically diagnosed as familial Alzheimer's disease due to a PSEN1 mutation.

One of two daughters also has the same mutation, G209A in the TM-IV of PS1 protein. Her mother had unspecified dementia that began at the age of 40s. PolyPhen2 and SIFT prediction suggested that G209A might be a damaging variant with high scores. 3D modeling revealed that G209A exchange could result significant changes in the PS1 protein.

Conclusion

We report a case of EOAD having probable novel PSEN1 (G209A) mutation verified with structural prediction.

A systematic review of familial Alzheimer's disease: Differences in presentation of clinical features among three mutated genes and potential ethnic differences

There are great diversities of clinical phenotypes among the various familial Alzheimer's disease (FAD) families. We aimed to systematically review all the previously reported cases of FAD and to perform comparisons between Asian and white patients. In this regard, we collected individual-level data from 658 pedigrees. We found that patients with presenilin 1 (PSEN1) mutations had the earliest age of onset (AOO; 43.3 ± 8.6 years, p < 0.001) and were more commonly affected by seizures, spastic paraparesis, myoclonus, and cerebellar signs (p < 0.001, p < 0.001, p = 0.003, and p = 0.002, respectively). Patients with PSEN2 mutations have a delayed AOO with longest disease duration and presented more frequently with disorientation (p = 0.03). Patients with amyloid precursor protein (APP) mutations presented more frequently with aggression (p = 0.02) and those with APP duplication presented more frequently with apraxia (p = 0.03). PSEN1 mutations before codon 200 had an earlier AOO than those having mutations after codon 200 (41.4 ± 8.0 years vs. 44.7 ± 8.7 years, p < 0.001). Because 42.9% of the mutations reported are novel, the mutation spectrum and clinical features in Asian FAD families could be different from that of whites. Asian patients with PSEN1 mutations presented more frequently with disorientation (p = 0.02) and personality change (p = 0.01) but less frequently with atypical clinical features. Asian patients with APP mutations presented less frequently with aphasia (p = 0.02). Thus, clinical features could be modified by underlying mutations, and Asian FAD patients may have different clinical features when compared with whites.

Identification of two novel mutations, PSEN1 E280K and PRNP G127S, in a Malaysian family

Alzheimer's disease (AD) is the most common form of dementia, which can be categorized into two main forms: early onset AD and late onset AD. The genetic background of early onset AD is well understood, and three genes, the APP, PSEN1, and PSEN2 have been identified as causative genes. In the current study, we tested three siblings from Malaysia who were diagnosed with early onset dementia, as well as their available family members. The family history was positive as their deceased father was similarly affected. Patients were tested for mutations in APP, PSEN1, PSEN2, and PRNP. A novel variant, E280K, was discovered in exon 8 of PSEN1 in the three siblings. In silico analyses with SIFT, SNAP, and PolyPhen2 prediction tools and three-dimensional modeling were performed, and the results suggested that the mutation is probably a pathogenic variant. Two additional pathogenic mutations were previously been described for codon 280, E280A, and E280G, which could support the importance of the E280 residue in the PS1 protein contributing to the pathogenic nature of E280K. Additional ten family members were screened for the E280K mutation, and all of them were negative. Six of them presented with a variety of neuropsychiatric symptoms, including learning disabilities, epilepsy, and schizophrenia, while four family members were asymptomatic. A novel PRNP G127S mutation was found in a step-niece of the three siblings harboring the PSEN1 E280K mutation. In silico predictions for PRNP G127S mutation suggested that this might be possibly a damaging variant. Additional studies to characterize PRNP G127S would be necessary to further understand the effects of this mutation.

The genetics of Alzheimer's disease

Alzheimer’s disease (AD) is a complex and heterogeneous neurodegenerative disorder, classified as either early onset (under 65 years of age), or late onset (over 65 years of age). Three main genes are involved in early onset AD: amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2). The apolipoprotein E (APOE) E4 allele has been found to be a main risk factor for late-onset Alzheimer’s disease. Additionally, genome-wide association studies (GWASs) have identified several genes that might be potential risk factors for AD, including clusterin (CLU), complement receptor 1 (CR1), phosphatidylinositol binding clathrin assembly protein (PICALM), and sortilin-related receptor (SORL1). Recent studies have discovered additional novel genes that might be involved in late-onset AD, such as triggering receptor expressed on myeloid cells 2 (TREM2) and cluster of differentiation 33 (CD33). Identification of new AD-related genes is important for better understanding of the pathomechanisms leading to neurodegeneration. Since the differential diagnoses of neurodegenerative disorders are difficult, especially in the early stages, genetic testing is essential for diagnostic processes. Next-generation sequencing studies have been successfully used for detecting mutations, monitoring the epigenetic changes, and analyzing transcriptomes. These studies may be a promising approach toward understanding the complete genetic mechanisms of diverse genetic disorders such as AD.

A novel PSEN1 H163P mutation in a patient with early-onset Alzheimer's disease: clinical, neuroimaging, and neuropathological findings

We report a novel presenilin 1 gene (PSEN1) mutation (H163P) in a patient with sporadic early-onset Alzheimer's disease. Clinical, molecular, and neuropathological examinations were performed on an index patient, who presented at the age of 34 years with depression and memory disturbances. At the age of 36 years, she exhibited seizures and myoclonus, cerebellar ataxia, and Parkinsonism. A novel mutation at codon 163 was found in PSEN1, which was changed from histidine to proline. Severe atrophy was noted in the frontal and temporal lobes of the brain. A histopathological examination of the frontal cortex revealed senile plaques and severe neurofibrillary tangles. PSEN1 codon 163 could be a mutational hot spot in early-onset Alzheimer's disease, and may result in a homogeneous phenotype similar to that of other patients with codon-163 mutations; thus, widening the spectrum of PSEN1 codon-163-linked phenotypes.

Identification of PSEN1 and PSEN2 gene mutations and variants in Turkish dementia patients

In order to assess the frequency of mutations in the known Alzheimer's disease causative genes in Turkish dementia patients we screened amyloid precursor protein (APP), PSEN1 and PSEN2 for mutations in a cohort of 98 Turkish dementia families. Six families were found to carry PSEN1 mutations (p.H163R, p.P264L, and p.H214Y) or variants suggested to cause the disease (p.L134R, p.L262V, and p.A396T). In 4 other families, previously reported PSEN2 variants were identified (p.R62H, p.R71W, p.M174V (n = 2), and p.S130L). The phenotype of the carriers varied from rapid progressing Alzheimer's disease to frontotemporal dementia, with spasticity and seizures also observed. Here we report a frequency of 11.2% of mutations and variants in the known Alzheimer disease genes in the dementia cohort studied and 24% in the early onset subgroup of patients, suggesting that mutations in these genes are not uncommon in Turkey and are associated with various phenotypes. We thus believe that genetic analysis should become a standardized diagnostic implement, not only for the identification of the genetic disease, but also for appropriate genetic counseling.

Clinicopathological concordance and discordance in three monozygotic twin pairs with familial Alzheimer's disease

AIM

Neuropathological examination of both individuals in a monozygotic (MZ) twin pair with Alzheimer's disease (AD) is rare, especially in the molecular genetic era. We had the opportunity to assess the concordance and discordance of clinical presentation and neuropathology in three MZ twin pairs with AD.

METHODS

The MZ twins were identified and characterised by the University of Washington Alzheimer's Disease Research Center. We reviewed the available clinical and neuropathological records for all six cases looking specifically for concordance and discordance of clinical phenotype, neuritic amyloid plaques (NP), neurofibrillary tangles (NFT) and Lewy related pathology (LRP).

RESULTS

Discordance in age of onset for developing AD in the MZ twins varied from 4 to 18 years. Clinical presentations also differed between twins. One twin presented with a dementia with Lewy Body clinical syndrome while the other presented with typical clinical AD. Neuropathology within the MZ twin pairs was concordant for NP and NFT, regardless of duration of disease, and was discordant for LRP. This difference was most marked in the late onset AD twin pair. One pair was found to have a mutation in presenilin-1 (PS1) (A79V) with remarkably late onset in a family member.

CONCLUSIONS

MZ twins with AD can vary considerably in age of onset, presentation and disease duration. The concordance of NP and NFT pathological change and the discordance of LRP support the concept that, in AD, the former are primarily under genetic control whereas the latter (LRP) is more influenced by disease duration and environmental factors. The A79V mutation in PS1 can be associated with very late onset of dementia.

The R269H mutation in presenilin-1 presenting as late-onset autosomal dominant Alzheimer's disease

Two siblings fulfilling clinical diagnostic criteria for late-onset Alzheimer's disease (AD) are reported. The family history suggested a total of nine individuals affected with AD in three generations with autosomal dominant disease transmission. Neurogenetic testing of the proband revealed a mutation, R269H, in the presenilin-1 (PS1) gene. Late-onset AD may be associated with deterministic PS1 mutations; these should be sought when the family history suggests autosomal dominant disease transmission.

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.

Mutations in presenilin 1, presenilin 2 and amyloid precursor protein genes in patients with early-onset Alzheimer's disease in Poland

Mutations in three causative genes have been identified in patients with an autosomal-dominant form of early-onset Alzheimer's disease (EOAD). To determine the spectrum of mutations in a group consisting of 40 Polish patients with clinically diagnosed familial EOAD and 1 patient with mild cognitive impairment (MCI) and family history of AD, we performed a screening for mutations in the presenilin 1 (PSEN1), presenilin 2 (PSEN2) and amyloid precursor protein (APP) genes. Four previously recognized pathogenic mutations in PSEN1 gene (H163R, M139V) and APP gene (T714A, V715A), and three novel putative mutations in PSEN1 gene (P117R and I213F) and PSEN2 gene (Q228L) were identified. The 34 patients with no mutations detected were older than the patients with mutations. A frequency of APOE4 allele was higher in this group. Frequency of mutations is relatively low (17%), possibly due to used operational definition of a patient with familial EOAD (a patient having at least one relative with early-onset dementia). It could be concluded that screening for mutations in the three genes could be included in a diagnostic program directed at patients with a positive family history or age of onset before 55 years.

Presenilins and Alzheimer's disease: biological functions and pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia in the elderly population. Dementia is associated with massive accumulation of fibrillary aggregates in various cortical and subcortical regions of the brain. These aggregates appear intracellularly as neurofibrillary tangles, extracellularly as amyloid plaques and perivascular amyloid in cerebral blood vessels. The causative factors in AD etiology implicate both, genetic and environmental factors. The large majority of early-onset familial Alzheimer's disease (FAD) cases are linked to mutations in the genes coding for presenilin 1 (PS1) and presenilin 2 (PS2). The corresponding proteins are 467 (PS1) and 448 (PS2) amino-acids long, respectively. Both are membrane proteins with multiple transmembrane regions. Presenilins show a high degree of conservation between species and a presenilin homologue with definite conservation of the hydrophobic structure has been identified even in the plant Arabidopsis thaliana. More than 50 missense mutations in PS1 and two missense mutations in PS2 were identified which are causative for FAD. PS mutations lead to the same functional consequence as mutations on amyloid precursor protein (APP), altering the processing of APP towards the release of the more amyloidogenic form 1-42 of Abeta (Abeta42). In this regard, the physical interaction between APP and presenilins in the endoplasmic reticulum has been demonstrated and might play a key role in Abeta42 production. It was hypothesized that PS1 might directly cleave APP. However, extracellular amyloidogenesis and Abeta production might not be the sole factor involved in AD pathology and several lines of evidence support a role of apoptosis in the massive neuronal loss observed. Presenilins were shown to modify the apoptotic response in several cellular systems including primary neuronal cultures. Some evidence is accumulating which points towards the beta-catenin signaling pathways to be causally involved in presenilin mediated cell death. Increased degradation of beta-catenin has been shown in brain of AD patients with PS1 mutations and reduced beta-catenin signaling increased neuronal vulnerability to apoptosis in cell culture models. The study of presenilin physiological functions and the pathological mechanisms underlying their role in pathogenesis clearly advanced our understanding of cellular mechanisms underlying the neuronal cell death and will contribute to the identification of novel drug targets for the treatment of AD.

High prevalence of pathogenic mutations in patients with early-onset dementia detected by sequence analyses of four different genes

Clinical differential diagnosis of early-onset dementia (EOD) includes familial Alzheimer disease (FAD) and hereditary prion disease. In both disease entities, postmortem brain histopathological examination is essential for unambiguous diagnosis. Mutations in the genes encoding the presenilins (PS1 and PS2) and amyloid precursor protein (APP) are associated with FAD, whereas mutations in the prion protein (PrP) gene are associated with prion disease. To investigate the proportion of EOD attributable to known genes, we prospectively (i.e., antemortem) screened these four genes for mutations by sequencing genomic PCR products from patients with EOD before age 60 years. Family history for dementia was positive (PFH) in 16 patients, negative (NFH) in 17 patients, and unknown (UFH) in 3 patients. In 12 patients, we found five novel mutations (in PS1, F105L; in PS2, T122P and M239I; and in PrP, Q160X and T188K) and five previously reported mutations (in APP, in three patients who were most likely unrelated, V717I; in PS1, A79V and M139V; and in PrP, P102L and T183A) that are all considered to be disease causing. Of these 12 patients, 9 had PFH. This indicates a detection rate of 56% (9/16) in patients with PFH. We found two mutations (APP V717I) in two of the three UFH patients, and only one mutation (PrP T188K) in 1 of the 17 patients with NFH. We conclude that because of the lack of specific antemortem diagnostic markers for FAD and hereditary prion disease, all four genes should be included in a molecular diagnostic program in patients with EOD who had PFH.

High frequency of mutations in four different disease genes in early-onset dementia

Heterozygous mutations in the genes for amyloid precursor protein (APP), the presenilins (PS1, PS2), prion protein (PrP), neuroserpin, and tau are associated with early-onset dementia (EOD) with or without neurological signs in the early disease stage. To investigate the proportion of EOD without early neurological signs attributable to known genes we prospectively (i.e., ante mortem) screened these six genes for mutations in 36 patients with EOD before age 60. Family history for dementia was positive (PFH) in 16, negative (NFH) in 17, and unknown (UFH) in 3 patients. In 12 patients, we found 5 novel mutations (PS1: F105L; PS2: T122P, M239I; PrP: Q160X, T188K) and 5 previously reported mutations (APP: in three most likely unrelated patients V717I; PS1: A79V, M139V; PrP: P102L, T183A) that all are considered disease causing. Of these 12 patients, 9 had PFH. This indicates a detection rate of 56% (9/16) in patients with PFH. We found 2 mutations (APP V717I) in 2 of the 3 the UFH-patients, and only 1 mutation (PrP T188K) in 1 of the 17 patients with NFH. No mutation was found in tau and neuroserpin genes. To date, three patients died and FAD, predicted by PS mutations in two patients, and prion disease, predicted by a PrP mutation in the third one, were histopathologically confirmed at autopsy. Up to now, mutation findings may be the most specific biomarkers for an ante mortem diagnosis of FAD or hereditary prion disease.

Transgenic mice with Alzheimer presenilin 1 mutations show accelerated neurodegeneration without amyloid plaque formation

Familial Alzheimer disease mutations of presenilin 1 (PS-1) enhance the generation of A beta1-42, indicating that PS-1 is involved in amyloidogenesis. However, PS-1 transgenic mice have failed to show amyloid plaques in their brains. Because PS-1 mutations facilitate apoptotic neuronal death in vitro, we did careful quantitative studies in PS-1 transgenic mice and found that neurodegeneration was significantly accelerated in mice older than 13 months (aged mice) with familial Alzheimer disease mutant PS-1, without amyloid plaque formation. However, there were significantly more neurons containing intracellularly deposited A beta42 in aged mutant transgenic mice. Our data indicate that the pathogenic role of the PS-1 mutation is upstream of the amyloid cascade.