A novel mutation (V89L) in the presenilin 1 gene in a family with early onset Alzheimer's disease and marked behavioural disturbances

Presenilin Gene Mutation-associated Psychosis: Phenotypic Characteristics and Clinical Implications

Although psychotic symptoms have been described in association with rare presenilin ( PSEN ) gene mutations underlying early-onset Alzheimer disease (AD), no contemporary reviews on this topic exist. The purpose of this review is to characterize the psychiatric phenotype (specifically with respect to psychosis) of PSEN1 and PSEN2 variant-associated AD. A PubMed search was completed in July 2023. Only articles that described individuals harboring a PSEN1 or PSEN2 mutation who experienced symptoms of psychosis were included in the review. Thirty-three articles describing 52 individuals were included in the review, as well as one other study that provided limited information pertaining to an additional 21 cases. While visual hallucinations were the most common psychotic symptom, followed by persecutory delusions, auditory hallucinations occurred in ~17% of individuals. In ~33% of the reviewed cases psychotic symptoms were present at or near disease onset, and 9 of these individuals experienced auditory hallucinations and/or delusions in the absence of visual hallucinations (~17% of all cases). In many cases, symptoms developed at a relatively young age. As presenilin gene variant-associated psychosis may resemble a primary psychotic disorder, clinicians should be vigilant with respect to screening for signs/symptoms suggestive of neurodegeneration in first-episode psychosis.

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.

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.

Cerebral Small Vessel Disease in Sporadic and Familial Alzheimer Disease

Alzheimer disease (AD) is the most common cause of dementia. Biological definitions of AD are limited to the cerebral burden of amyloid β plaques, neurofibrillary pathology, and neurodegeneration. However, current evidence suggests that various features of small vessel disease (SVD) are part of and covertly modify both sporadic and familial AD. Neuroimaging studies suggest that white matter hyperintensities explained by vascular mechanisms occurs frequently in the AD spectrum. Recent advances have further emphasized that frontal periventricular and posterior white matter hyperintensities are associated with cerebral amyloid angiopathy in familial AD. Although whether SVD markers precede the classically recognized biomarkers of disease is debatable, post-mortem studies show that SVD pathology incorporating small cortical and subcortical infarcts, microinfarcts, microbleeds, perivascular spacing, and white matter attenuation is commonly found in sporadic as well as in mutation carriers with confirmed familial AD. Age-related cerebral vessel pathologies such as arteriolosclerosis and cerebral amyloid angiopathy modify progression or worsen risk by shifting the threshold for cognitive impairment and AD dementia. The incorporation of SVD as a biomarker is warranted in the biological definition of AD. Therapeutic interventions directly reducing the burden of brain amyloid β have had no major impact on the disease or delaying cognitive deterioration, but lowering the risk of vascular disease seems the only rational approach to tackle both early- and late-onset AD dementia.

A Pathogenic Presenilin-1 Val96Phe Mutation from a Malaysian Family

Presenilin-1 (PSEN1) is one of the causative genes for early onset Alzheimer's disease (EOAD). Recently, emerging studies have reported several novel PSEN1 mutations among Asians. In this study, a PSEN1 Val96Phe mutation was discovered in two siblings from Malaysia with a strong family history of disease. This is the second report of PSEN1 Val96Phe mutation among EOAD patients in Asia and in the world. Patients presented symptomatic changes in their behaviors and personality, such as apathy and withdrawal in their 40s. Previous cellular studies with COS1 cell lines revealed the mutation increased the amyloid-β42 (Aβ42) productions. In the present study, whole-exome sequencing was performed on the two siblings with EOAD, and they were analyzed against the virtual panel of 100 genes from various neurodegenerative diseases. In silico modeling was also performed on PSEN1 Val96Phe mutation. This mutation was located on the first transmembrane helix of PSEN1 protein, resulting significant intramolecular stresses in the helices. This helical domain would play a significant role in γ-secretase cleavage for the increased Aβ42 productions. Several other adjacent mutations were reported in this helical domain, including Ile83Thr or Val89Leu. Our study suggested that perturbations in TMI-HLI-TMII regions could also be associated with C-terminal fragment accumulation of APP and enhanced amyloid productions.

Neurons derived from sporadic Alzheimer's disease iPSCs reveal elevated TAU hyperphosphorylation, increased amyloid levels, and GSK3B activation

BACKGROUND

Alzheimer's disease (AD) is the most common type of dementia, affecting one in eight adults over 65 years of age. The majority of AD cases are sporadic, with unknown etiology, and only 5% of all patients with AD present the familial monogenic form of the disease. In the present study, our aim was to establish an in vitro cell model based on patient-specific human neurons to study the pathomechanism of sporadic AD.

METHODS

We compared neurons derived from induced pluripotent stem cell (iPSC) lines of patients with early-onset familial Alzheimer's disease (fAD), all caused by mutations in the PSEN1 gene; patients with late-onset sporadic Alzheimer's disease (sAD); and three control individuals without dementia. The iPSC lines were differentiated toward mature cortical neurons, and AD pathological hallmarks were analyzed by RT-qPCR, enzyme-linked immunosorbent assay, and Western blotting methods.

RESULTS

Neurons from patients with fAD and patients with sAD showed increased phosphorylation of TAU protein at all investigated phosphorylation sites. Relative to the control neurons, neurons derived from patients with fAD and patients with sAD exhibited higher levels of extracellular amyloid-β 1-40 (Aβ_1-40) and amyloid-β 1-42 (Aβ_1-42). However, significantly increased Aβ_1-42/Aβ_1-40 ratios, which is one of the pathological markers of fAD, were observed only in samples of patients with fAD. Additionally, we detected increased levels of active glycogen synthase kinase 3 β, a physiological kinase of TAU, in neurons derived from AD iPSCs, as well as significant upregulation of amyloid precursor protein (APP) synthesis and APP carboxy-terminal fragment cleavage. Moreover, elevated sensitivity to oxidative stress, as induced by amyloid oligomers or peroxide, was detected in both fAD- and sAD-derived neurons.

CONCLUSIONS

On the basis of the experiments we performed, we can conclude there is no evident difference except secreted Aβ_1-40 levels in phenotype between fAD and sAD samples. To our knowledge, this is the first study in which the hyperphosphorylation of TAU protein has been compared in fAD and sAD iPSC-derived neurons. Our findings demonstrate that iPSC technology is suitable to model both fAD and sAD and may provide a platform for developing new treatment strategies for these conditions.

The novel PSEN1 M84V mutation associated to frontal dysexecutive syndrome, spastic paraparesis, and cerebellar atrophy in a dominant Alzheimer's disease family

We identified the novel PSEN1 pathogenic mutation M84V in 3 patients belonging to a large kindred affected by autosomal dominant Alzheimer's disease (AD). The clinical phenotype was characterized by early onset dementia in 14 affected subjects over 3 generations. Detailed clinical, imaging and genetic assessment was performed. We highlighted the presence of unusual symptoms such as frontal executive syndrome, psychosis and spastic paraparesis in these patients. Spastic paraparesis has been reported in other PSEN1 mutations in adjacent codons, suggesting that the position of the genetic defect may affect the clinical expression, although this phenotype can occur in mutations throughout the whole PSEN1 gene. Brain magnetic resonance imaging showed diffuse cortical atrophy, but also atrophy of cerebellar lobules, mainly involving Crus I, in 2 patients without cerebellar motor deficits. These neuroimaging results were consistent with recent findings about the association between sporadic AD and distinct and circumscribed cerebellar atrophy. The present work acknowledged the novel PSEN1 pathogenic mutation M84V and might contribute to the ongoing debate about the involvement of cerebellum in AD.

Early psychiatrics symptoms in familial Alzheimer's disease with presenilin 1 mutation (I83T)

Several clinical phenotypes were associated with presenilin 1 (PSEN1) mutation in early-onset familial Alzheimer's disease (EOFAD). We report the clinical phenotype of two members of a familial dementia kindred who presented with EOFAD and early psychiatric syndrome as behavioral abnormalities. Sequence analysis of the index patient and his brother's PSEN1 transcript revealed a novel T > C transition in exon 4 which was determined as a missense substitution at position 248 of the coding sequence (cDNA. 248T > C).

Corticobasal Syndrome in a Family with Early-Onset Alzheimer's Disease Linked to a Presenilin-1 Gene Mutation

BACKGROUND

Alzheimer's disease (AD) is the second-most frequent cause underlying corticobasal syndrome (CBS). However, a reliable diagnosis using clinical, neuropsychological, or neuroimaging approaches has not yet been achieved.

METHODS

Clinical, neuropsychological, imaging, and neuropathology studies were undertaken in a large Spanish family with early-onset familial AD (EOFAD) carrying a Met233Leu mutation linked to presenilin-1 gene (PSEN-1).

RESULTS

Two of three examined members of this family presented with the usual amnestic pattern. At the age of 47 years, a third family member, in whom pathology was later confirmed, developed prominent CBS combined with severe neuropsychiatric and behavioral disturbances resembling those often found in EOFAD.

CONCLUSION

Although CBS in EOFAD appears to be rare, demonstration of a linkage to PSEN-1 gene mutations may permit in vivo diagnosis.

Pilot whole-exome sequencing of a German early-onset Alzheimer's disease cohort reveals a substantial frequency of PSEN2 variants

Early-onset Alzheimer's disease (EOAD) accounts for 1%-2% of all Alzheimer's disease (AD) subjects, with large variation in the reported genetic contribution of known dementia genes. In this pilot study, we genetically characterized a German EOAD cohort (23 subjects) by whole-exome sequencing, capturing variants in all recognized AD and frontotemporal dementia genes. After variant filtering, we identified 7 events of altogether 6 different rare variants in 6 subjects, including 4 novel variants. Four of the 6 variants, observed in 5 different index subjects (5/23 = 22%), were considered to be possibly pathogenic. These included 2 presenilin 2 (PSEN2) variants (p.N141I-previously denoted as a Volga German variant, observed in 2 index subjects; and p.L238P), 1 amyloid precursor protein (p.I716M), and 1 presenilin 1 (ΔE9). Using a control exome data set of 96 ethnically matched neurodegenerative disease controls (Parkinson's disease), we identified only 1 variant (PSEN2 p.T18M) (1%), demonstrating a significantly higher mutational burden in the EOAD group (p > 0.0001). Our findings demonstrate a substantial frequency of variants in dementia genes in EOAD, including several seemingly "sporadic" subjects. This indicates that heritability in EOAD might be higher than assumed. The finding of 3 subjects carrying potential pathogenic PSEN2 variants suggests that, in specific populations PSEN2 variants might be as frequent as (or more frequent than) presenilin 1, for example, in German populations which are influenced by Volga German heritage. Variants in AD genes were also associated with rare phenotypes such as frontal AD or primary progressive aphasia, demonstrating the need to screen AD genes in frontotemporal dementia-like phenotypes.

Seizures in Alzheimer's disease

Alzheimer's disease (AD) increases the risk for late-onset seizures and neuronal network abnormalities. An elevated co-occurrence of AD and seizures has been established in the more prevalent sporadic form of AD. Recent evidence suggests that nonconvulsive network abnormalities, including seizures and other electroencephalographic abnormalities, may be more commonly found in patients than previously thought. Patients with familial AD are at an even greater risk for seizures, which have been found in patients with mutations in PSEN1, PSEN2, or APP, as well as with APP duplication. This review also provides an overview of seizure and electroencephalography studies in AD mouse models. The amyloid-β (Aβ) peptide has been identified as a possible link between AD and seizures, and while Aβ is known to affect neuronal activity, the full-length amyloid precursor protein (APP) and other APP cleavage products may be important for the development and maintenance of cortical network hyperexcitability. Nonconvulsive epileptiform activity, such as seizures or network abnormalities that are shorter in duration but may occur with higher frequency, may contribute to cognitive impairments characteristic of AD, such as amnestic wandering. Finally, the review discusses recent studies using antiepileptic drugs to rescue cognitive deficits in AD mouse models and human patients. Understanding the mechanistic link between epileptiform activity and AD is a research area of growing interest. Further understanding of the connection between neuronal hyperexcitability and Alzheimer's as well as the potential role of epileptiform activity in the progression of AD will be beneficial for improving treatment strategies.

Probable novel PSEN2 Val214Leu mutation in Alzheimer's disease supported by structural prediction

Background

PSEN2 mutations are rare variants, and fewer than 30 different PSEN2 mutations have been found. So far, it has not been reported in Asia.

Case presentation

PSEN2 mutation at codon 214 for predicting a valine to leucine substitution was found in a 70-year-old woman, who showed a dementia of the Alzheimer type. We did not find the mutation in 614 control chromosomes. We also predicted the structures of presenilin 2 protein with native Val 214 residue and Leu 214 mutation, which revealed significant structural changes in the region.

Conclusion

It could be a novel mutation verified with structural prediction in a patient with Alzheimer’s disease.

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.

Genetics of dementia: update and guidelines for the clinician

With increased frequency, clinical geneticists are asked for genetic advice on the heredity of dementia in families. Alzheimer's disease is in most cases a complex disease, but may be autosomal dominant inherited. Mutations in the PSEN1 gene are the most common genetic cause of early onset Alzheimer's disease, whereas APP and PSEN2 gene mutations are less frequent. Familial frontotemporal dementia may be associated with a mutation in the MAPT or GRN gene, or with a repeat expansion in the C9orf72 gene. All these genes show autosomal dominant inheritance with a high penetrance. Although Alzheimer's disease and frontotemporal dementia are clinically distinguishable entities, phenotypical overlap may occur. Rarely, dementia is caused by mutations in other autosomal dominant genes or by genetic defects with autosomal recessive, X-linked dominant or mitochondrial inheritance. The inherited forms of frontotemporal dementia and Alzheimer's disease show a large phenotypic variability also within families, resulting in many remaining uncertainties for mutation carriers. Therefore, genetic counseling before performing genetic testing is essential in both symptomatic individuals and healthy at risk relatives. This review provides an overview of the genetic causes of dementia and discusses all aspects relevant for genetic counseling and testing. Furthermore, based on current knowledge, we provide algorithms for genetic testing in patients with early onset Alzheimer's disease or frontotemporal dementia.

The paradox of syndromic diversity in Alzheimer disease

Variant syndromes of Alzheimer disease (AD), led by deficits that extend beyond memory dysfunction, are of considerable clinical and neurobiological importance. Such syndromes present major challenges for both diagnosis and monitoring of disease, and serve to illustrate the apparent paradox of a clinically diverse group of disorders underpinned by a common histopathological substrate. This Review focuses on the most common variant AD phenotypes: posterior cortical atrophy, logopenic variant primary progressive aphasia and frontal variant AD. The neuroanatomical, molecular and pathological correlates of these phenotypes are highlighted, and the heterogeneous clinical presentations of the syndromes are discussed in the context of the emerging network paradigm of neurodegenerative disease. We argue that these apparently diverse clinical phenotypes reflect the differential involvement of a common core temporoparietofrontal network that is vulnerable to AD. According to this interpretation, the network signatures corresponding to AD variant syndromes are produced by genetic and other modulating factors that have yet to be fully characterized. The clinical and neurobiological implications of this network paradigm in the quest for disease-modifying treatments are also explored.

Correlating familial Alzheimer's disease gene mutations with clinical phenotype

Alzheimer's disease (AD) causes devastating cognitive impairment and an intense research effort is currently devoted to developing improved treatments for it. A minority of cases occur at a particularly young age and are caused by autosomal dominantly inherited genetic mutations. Although rare, familial AD provides unique opportunities to gain insights into the cascade of pathological events and how they relate to clinical manifestations. The phenotype of familial AD is highly variable and, although it shares many clinical features with sporadic AD, it also possesses important differences. Exploring the genetic and pathological basis of this phenotypic heterogeneity can illuminate aspects of the underlying disease mechanism, and is likely to inform our understanding and treatment of AD in the future.

Clinical picture of a patient with a novel PSEN1 mutation (L424V)

Young onset dementia raises concern about familial and non degenerative dementias. We describe a patient with early dementia. At the age of 26, a woman developed symptoms of anorexia nervosa, at 30 a memory and attention deficit, and at 34 abnormal behavior with impulsivity, aggression, and dysexecutive disorder. At 36 she showed aphasia, stereotyped behavior, hyperreflexia, grasping reflex, urinary incontinence, myoclonus, and seizures. Blood and cerebrospinal fluid were normal. Brain computed tomography and single photon emission computed tomography showed diffuse cortico-subcortical atrophy and frontotemporoparietal hypoperfusion. A Leu424Val mutation was present in PSEN1 gene. PSEN1 mutations can produce Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies phenotypes, or a combination of them. It has been proposed that the mutation type and location may influence the molecular pathogenesis and thus PSEN1 would represent a molecular connexion between these entities. This case shows a novel PSEN1 mutation with outstanding amnesic and frontal symptoms.

Presenilin 1 interacts with acetylcholinesterase and alters its enzymatic activity and glycosylation

Presenilin 1 (PS1) plays a critical role in the gamma-secretase processing of the amyloid precursor protein to generate the beta-amyloid peptide, which accumulates in plaques in the pathogenesis of Alzheimer's disease (AD). Mutations in PS1 cause early onset AD, and proteins that interact with PS1 are of major functional importance. We report here the coimmunoprecipitation of PS1 and acetylcholinesterase (AChE), an enzyme associated with amyloid plaques. Binding occurs through PS1 N-terminal fragment independent of the peripheral binding site of AChE. Subcellular colocalization of PS1 and AChE in cultured cells and coexpression patterns of PS1 and AChE in brain sections from controls and subjects with sporadic or familial AD indicated that PS1 and AChE are located in the same intracellular compartments, including the perinuclear compartments. A PS1-A246E pathogenic mutation expressed in transgenic mice leads to decreased AChE activity and alteration of AChE glycosylation and the peripheral binding site, which may reflect a shift in protein conformation and disturbed AChE maturation. In both the transgenic mice and humans, mutant PS1 impairs coimmunoprecipitation with AChE. The results indicate that PS1 can interact with AChE and influence its expression, supporting the notion of cholinergic-amyloid interrelationships.

Frontotemporal dementia-like phenotypes associated with presenilin-1 mutations

Frontal behavioral changes may be the presenting features of single-photon emission tomography (presenilin-1 [PS-1]) mutations, the most common cause of familial Alzheimer's disease (AD). The authors describe a PS-1 (M233L) mutation with the features of frontotemporal dementia (FTD) and review the literature. PS-1 mutations may produce FTD-like phenotypes with the neuropathology of AD. Some PS-1 mutations have additional Pick's bodies, a neuropathological marker of FTD, and a report of a PS-1 (G183V) mutation found Pick's bodies without amyloid plaques. The patient and the literature suggest that PS-1 mutations result in an overlapping continuum of the clinical and neuropathological features of AD and FTD. In PS-1 mutations, the expression of AD or FTD may depend on the degree of loss of function of the PS-1 gene and the resultant tau pathophysiology.

Genética de las enfermedades neurodegenerativas más prevalentes

A large number of mutations and polymorphisms associated with neurodegenerative disorders have been described during the last years. These findings have been helpful to improve our knowledge about the pathogenesis of these disorders. In this review we describe the genetic alterations and variants that cause or predispose to develop several neurodegenerative disorders, such as Huntington's disease, Alzheimer's disease, frontotemporal dementia, Parkinson's disease and other parkinsonisms. We also comment on the possible pathogenic mechanism of these mutations, clinical features and the usefulness of this information for the diagnosis and management of these disorders.

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.

Two domains within the first putative transmembrane domain of presenilin 1 differentially influence presenilinase and gamma-secretase activity

Presenilins (PS) are thought to contain the active site for presenilinase endoproteolysis of PS and gamma-secretase cleavage of substrates. The structural requirements for PS incorporation into the gamma-secretase enzyme complex, complex stability and maturation, and appropriate presenilinase and gamma-secretase activity are poorly understood. We used rescue assays to identify sequences in transmembrane domain one (TM1) of PS1 required to support presenilinase and gamma-secretase activities. Swap mutations identified an N-terminal TM1 domain that is important for gamma-secretase activity only and a C-terminal TM1 domain that is essential for both presenilinase and gamma-secretase activities. Exchange of residues 95-98 of PS1 (sw95-98) completely abolishes both activities while the familial Alzheimer's disease mutation V96F significantly inhibits both activities. Reversion of residue 96 back to valine in the sw95-98 mutant rescues PS function, identifying V96 as the critical residue in this region. The TM1 mutants do not bind to an aspartyl protease transition state analog gamma-secretase inhibitor, indicating a conformational change induced by the mutations that abrogates catalytic activity. TM1 mutant PS1 molecules retain the ability to interact with gamma-secretase substrates and gamma-secretase complex members, although Nicastrin stability is decreased by the presence of these mutants. gamma-Secretase complexes that contain V96F mutant PS1 molecules display a partial loss of function for gamma-secretase that alters the ratio of amyloid-beta peptide species produced, leading to the amyloid-beta peptide aggregation that causes familial Alzheimer's disease.

Linkage to chromosome 14q in Alzheimer's disease (AD) patients without psychotic symptoms

Cases of early onset AD have been attributed to three genes, PSEN1, PSEN2, and APP, while the only gene consistently associated with late onset AD (LOAD) is APOE. Several genome scans have now been performed for LOAD with inconsistent findings in several genomic regions, possibly reflecting the underlying genetic heterogeneity. Many lines of evidence suggest that the absence or presence of psychotic symptoms, common in AD, might delineate distinct etiologic disease subtypes. We have performed a genome scan of 148 AD pedigrees (ages of onset more than 50 years) including the presence or absence of delusions and hallucinations as covariates. This approach identified linkage to a locus on chromosome 14q24.3, close to the PSEN1 locus (LOD score 3.91; genome-wide empirical P = 0.052), derived from individuals that do not have co-morbid hallucinations. The finding appears stronger (LOD score 5.74; genome-wide empirical P = 0.048) in families that include younger affected members (AAO between 50 and 65 years), however it is not present without the inclusion of the covariate and we observe no correlation between the presence of hallucinations and the age of onset. A mutation screen of PSEN1 did not detect any coding region or splice site mutations. This linkage finding suggests the presence of a gene causing AD without co-morbid hallucinations and with an earlier (yet not early) age at onset (AAO) in the 14q24 region. This region requires further study to replicate the finding and identify the genetic variant responsible for the linkage.

Reduced KIAA0471 mRNA expression in Alzheimer's patients: a new candidate gene product linked to the disease?

Alzheimer's disease (AD) phenotype complexity raises the question whether genetic features remain unknown. Although a few percentage of patients are familial cases linked to mutations in amyloid precursor protein, presenilin 1 or presenilin 2 genes, the remainder are considered mainly sporadic late-onset cases with a complex etiology. However, changes in gene expression or other genetic features of the individual can clearly contribute to develop the illness. Consequently, in this paper we have focused on the identification of new genes, the expression of which is altered in AD. We used the technique of differential display reverse transcriptase-polymerase chain reaction (DDRT-PCR) in order to study the gene expression differences in brain tissue from patients in an advanced stage of AD. After studying medial septum and hippocampus brain areas, we found an inhibition of the KIAA0471 gene expression in three out of six AD patients, including one with a presenilin 1 gene mutation. This gene encodes for a large protein that presents, in its predicted form, 95% homology with IDN4-GGTR sequences. These results may provide significant clues for understanding the molecular mechanisms underlying septohippocampal neurodegeneration. In addition, they may open a new area of research for diagnostic and therapeutic tools, the relevance of which is also considered.

Young onset dementia

Young onset dementia is a challenging clinical problem with potentially devastating medical and social consequences. The differential diagnosis is wide, and includes a number of rare sporadic and hereditary diseases. However, accurate diagnosis is often possible, and all patients should be thoroughly investigated to identify treatable processes. This review presents an approach to the diagnosis, investigation, and management of patients with young onset dementia, with particular reference to common and treatable causes.

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.

Neuropsychological study of familial Alzheimer's disease caused by mutation E280A in the presenilin 1 gene

In Antioquia, Colombia, investigators have recently discovered the largest family with the E280A mutation in the presenilin 1 gene that causes one type of familial Alzheimer's disease (FAD). The current study compares two groups within this family: those diagnosed with Alzheimer's disease (AD) in its early stage (nine subjects) and relatives (carriers) who did not show any signs of dementia (nine subjects). A battery of the following neuropsychological tests was administered to subjects in both groups: the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), a Phonological Verbal Fluency test, the Visual "A" Cancellation Test, memory of three phrases, the Rey-Osterrieth Complex Figure, and the Trail Making Test Part A. Statistical analyses of the average test scores of each group showed that the AD group scored significantly (p < 0.01 or p < 0.05) lower on 29 of the 43 neuropsychological variables measured (67 percent). Therefore, this specific battery was useful in discriminating subjects with AD from their healthy relatives who are carriers of the disease. The AD group as a whole presented slight dementia with predominant deficits in memory, language, praxis, and attention. This profile is similar to those reported in subjects with sporadic AD in its early stage and confirms the findings found in other neuropsychological studies of subjects with FAD linked to mutations in chromosome 14.