Familial frontotemporal dementia associated with a novel presenilin-1 mutation

Presenilin deficiency enhances tau phosphorylation and its secretion

Alzheimer's disease (AD) is characterized by the accumulation of abnormally folded amyloid β-protein (Aβ) in the brain parenchyma and phosphorylated tau in neurons. Presenilin (PS, PSEN) 1 and PS2 are essential components of γ-secretase, which is responsible for the cleavage of amyloid precursor protein (APP) to generate Aβ. PSEN mutations are associated with tau aggregation in frontotemporal dementia, regardless of the presence or absence of Aβ pathology. However, the mechanism by which PS regulates tau aggregation is still unknown. Here, we found that tau phosphorylation and secretion were significantly increased in PS double-knock-out (PS1/2-/-) fibroblasts compared with wild-type fibroblasts. Tau-positive vesicles in the cytoplasm were significantly increased in PS1/2-/- fibroblasts. Active GSK-3β was increased in PS1/2-/- fibroblasts, and inhibiting GSK3β activity in PS1/2-/- fibroblasts resulted in decreased tau phosphorylation and secretion. Transfection of WT human PS1 and PS2 reduced the secretion of phosphorylated tau and active GSK-3β in PS1/2-/- fibroblasts. However, PS1D257A without γ-secretase activity did not decrease the secretion of phosphorylated tau. Furthermore, nicastrin deficiency also increased tau phosphorylation and secretion. These results suggest that deficient PS complex maturation may increase tau phosphorylation and secretion. Thus, our studies discover a new pathway by which PS regulates tau phosphorylation/secretion and pathology independent of Aβ and suggest that PS serves as a potential therapeutic target for treating neurodegenerative diseases involving tau aggregation.

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.

The 100 Most Cited Kluver-Bucy Research Articles: A Bibliometric Analysis

Kluver-Bucy Syndrome (KBS) is a rare neuropsychiatric disorder characterized by hyperorality, hypersexuality, bulimia, visual agnosia, and amnesia due to lesions affecting bilateral temporal lobes. It is attributed to a multitude of causes, including stroke, herpes simplex encephalitis, Alzheimer's disease, and head trauma. Current treatments for KBS include symptomatic management with antipsychotics, mood stabilizers, carbamazepine, and selective serotonin reuptake inhibitors. The bibliometric analysis was done to reflect the relevance and understanding of KBS in recent literature. The SCOPUS database was utilized to conduct a search for all articles with the terms "Kluver-Bucy" and "Kluver Bucy" from January 1, 1955 (the first available articles from the search) to February 1, 2023. The parameters included in this analysis were article title, citation numbers, citations per year, authors, institutions, publishing journals, country of origin, Source Normalized Impact per Paper, and Scopus CiteScore. Since 1937, when Kluver-Bucy Syndrome was first defined, the publications on KBS have steadily increased, with up to six publications a year in 2002. The most common institutions were SUNY Upstate Medical University, VA Medical Center, and the State University of New York (SUNY) System. Seven of these papers were published in Neurology. Almost 75% of the articles were published in journals of medicine and neuroscience. This is the first bibliometric analysis to evaluate the most influential publications about Kluver-Bucy Syndrome. A majority of the research is case-based and there is a dearth of clinical trials to identify the exact pathophysiology and physiotherapy management, possibly owing to the rarity of the disease. Our research suggests that there may be a significant overlap between Sanfilippo syndrome and KBS, suggesting that refined guidelines for establishing diagnosis may be required for children. Our study could bring a renewed interest in this field and lead to additional research focused on understanding the pathophysiology of KBS in order to promote the development of novel diagnostics and treatment.

Identification and Clinical Analysis of the First Nonsense Mutation in the PSEN1 Gene in a Family With Acute Encephalopathy and Retinitis Pigmentosa

In the present study, we investigated the genetic variation in a family with acute encephalopathy and retinitis pigmentosa. Nine of 25 people in this family underwent genetic testing. Three family members, namely, the proband and the proband's two sisters, showed symptoms resembling those of meningoencephalitis and simultaneously suffered from retinitis pigmentosa. Whole-exome sequencing and Sanger sequencing identified a heterozygous mutation, chr14: 73673106 c.881G>A (p.W294^*), in the presenilin 1 (PSEN1) gene in these three family members, and the SWISS-MODEL server predicted the formation of a truncated protein. This mutation was not found in the asymptomatic family members. This mutation is a newly discovered nonsense mutation that results in a truncated protein. Although the current genetic evidences may indicate the likelihood of association, further investigations are needed to establish the genotype and phenotype relationship.

Calcium Signaling in ß-cell Physiology and Pathology: A Revisit

Pancreatic beta (β) cell dysfunction results in compromised insulin release and, thus, failed regulation of blood glucose levels. This forms the backbone of the development of diabetes mellitus (DM), a disease that affects a significant portion of the global adult population. Physiological calcium (Ca²⁺) signaling has been found to be vital for the proper insulin-releasing function of β-cells. Calcium dysregulation events can have a dramatic effect on the proper functioning of the pancreatic β-cells. The current review discusses the role of calcium signaling in health and disease in pancreatic β-cells and provides an in-depth look into the potential role of alterations in β-cell Ca²⁺ homeostasis and signaling in the development of diabetes and highlights recent work that introduced the current theories on the connection between calcium and the onset of diabetes.

Frontotemporal dementia spectrum: first genetic screen in a Greek cohort

Frontotemporal dementia (FTD) is a heterogeneous group of neurodegenerative syndromes associated with several causative and susceptibility genes. Herein, we aimed to determine the incidence of the most common causative dementia genes in a cohort of 118 unrelated Greek FTD spectrum patients. We also screened for novel possible disease-associated variants in additional 21 genes associated with FTD or amyotrophic lateral sclerosis. Pathogenic or likely pathogenic variants were identified in 16 cases (13.6%). These included repeat expansions in C9orf72 and loss-of-function GRN variants, and likely pathogenic variants in TARDBP, MAPT, and PSEN1. We also identified 14 variants of unknown significance in other rarer FTD or amyotrophic lateral sclerosis genes that require further segregation and functional analysis. Our genetic screen revealed a high genetic burden in familial Greek FTD cases (30.4%), whereas only two of the sporadic cases (3.5%) carried a likely pathogenic variant. A substantial number of familial cases still remain without an obvious causal variant, suggesting the existence of other FTD genetic causes besides those currently screened in clinical routine.

Bax inhibitor 1 is a γ-secretase-independent presenilin-binding protein

β-amyloid is regarded by some scientists to be the cause of Alzheimer’s disease (AD). One of the strongest arguments against this hypothesis is the presence of hundreds of AD-causing mutations in presenilin, but none in the other three components of γ-secretase. This observation implies a γ-secretase–independent function of presenilin. To understand such a putative function, discovery of presenilin-binding proteins represents an important first step. In this study, we report the identification of Bax-inhibitor 1 (BI1) as a stable interacting partner of presenilin 1 (PS1), but not the intact γ-secretase. Our results link PS1 to BI1, a protein thought to play a role in apoptosis and calcium channel regulation. This finding opens a range of possibilities for the investigation of PS1 function and AD genesis.

Presenilin is the catalytic subunit of γ-secretase, a four-component intramembrane protease responsible for the generation of β-amyloid (Aβ) peptides. Over 200 Alzheimer’s disease-related mutations have been identified in presenilin 1 (PS1) and PS2. Here, we report that Bax-inhibitor 1 (BI1), an evolutionarily conserved transmembrane protein, stably associates with PS1. BI1 specifically interacts with PS1 in isolation, but not with PS1 in the context of an assembled γ-secretase. The PS1–BI1 complex exhibits no apparent proteolytic activity, as judged by the inability to produce Aβ40 and Aβ42 from the substrate APP-C99. At an equimolar concentration, BI1 has no impact on the proteolytic activity of γ-secretase; at a 200-fold molar excess, BI1 reduces γ-secretase activity nearly by half. Our biochemical study identified BI1 as a PS1-interacting protein, suggesting additional functions of PS1 beyond its involvement in γ-secretase.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Identification of PSEN1 mutations p.M233L and p.R352C in Han Chinese families with early-onset familial Alzheimer's disease

Early-onset familial Alzheimer's disease (EOFAD) is characterized by the onset of dementia symptoms before 65 years, positive family history, high genetic predisposition, and an autosomal dominant inheritance. We aimed to investigate mutations and to characterize phenotypes in Chinese EOFAD families. Detailed clinical assessments and genetic screening for mutations in the presenilin 1 (PSEN1), presenilin 2, amyloid precursor protein, and APOE genes were carried out in 4 EOFAD families. Two PSEN1 mutations (p.R352C and p.M233L) were identified in 2 EOFAD families, respectively. Mutation p.M233L was associated with prominent very early onset, rapidly progressive dementia, and neurologic symptoms, whereas p.R352C was associated with a progressive dementia, psychiatric syndrome, and chronic disease course. Both mutations are predicted to be pathogenic. Our results showed that mutations in PSEN1 gene might be common in Chinese EOFAD families.

Development and validation of pedigree classification criteria for frontotemporal lobar degeneration

IMPORTANCE

A significant portion of frontotemporal lobar degeneration (FTLD) is due to inherited gene mutations, and we are unaware of a large sequential series that includes a recently discovered inherited cause of FTLD. There is also great need to develop clinical tools and approaches that will assist clinicians in the identification and counseling of patients with FTLD and their families regarding the likelihood of an identifiable genetic cause.

OBJECTIVES

To ascertain the frequency of inherited FTLD and develop validated pedigree classification criteria for FTLD that provide a standardized means to evaluate pedigree information and insight into the likelihood of mutation-positive genetic test results for C9orf72, MAPT, and GRN.

DESIGN

Information about pedigrees and DNA was collected from 306 serially assessed patients with a clinical diagnosis of FTLD. This information included gene test results for C9orf72, MAPT, and GRN. Pedigree classification criteria were developed based on a literature review of FTLD genetics and pedigree tools and then refined by reviewing mutation-positive and -negative pedigrees to determine differentiating characteristics.

SETTING

Academic medical center.

PARTICIPANTS

Patients with FTLD.

MAIN OUTCOMES AND MEASURES

Familial risk.

RESULTS

The rate of C9orf72, MAPT, or GRN mutation-positive FTLD in this series was 15.4%. Categories designating the risk level for hereditary cause were termed high, medium, low, apparent sporadic, and unknown significance. Thirty-nine pedigrees (12.7%) met criteria for high, 31 (10.1%) for medium, 46 (15.0%) for low, 91 (29.7%) for apparent sporadic, and 99 (32.4%) for unknown significance. The mutation-detection rates were as follows: high, 64.1%; medium, 29%; low, 10.9%; apparent sporadic, 1.1%; and unknown significance, 7.1%. Mutation-detection rates differed significantly between the high and other categories.

CONCLUSIONS AND RELEVANCE

Mutation rates are high in FTLD spectrum disorders, and the proposed criteria provide a validated standard for the classification of FTLD pedigrees. The combination of pedigree criteria and mutation-detection rates has important implications for genetic counseling and testing in clinical settings.

Different clinical phenotypes in siblings with a presenilin-1 P264L mutation

BACKGROUND

Mutations in the presenilin-1 gene (PSEN1) have been identified in autosomal dominant early-onset cases of Alzheimer's disease (AD).

AIMS

To investigate different clinical phenotypes of siblings possessing the same heterozygous P264L mutation in the PSEN1 gene.

METHODS

We evaluated clinical features, neuroimaging results, and neuropsychological examinations. The PSEN1 gene and other dementia-related gene mutations were screened.

RESULTS

We clinically diagnosed the proband as atypical AD with frontotemporal dementia features and diagnosed the elder brother of the proband as typical AD, based on neuropsychological symptoms and a brain imaging examination including amyloid imaging data. A heterozygous P264L mutation in the PSEN1 gene was identified in both siblings.

CONCLUSION

This study is one of few reports of AD siblings possessing the same mutation but exhibiting different clinical phenotypes in a Japanese family possessing a P264L mutation in the PSEN1 gene. The current results suggest that unknown modifiers, including both genetic and epigenetic factors, may alter the pathological and clinical phenotypes of a genetically predetermined disease.

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.

Transgenic mouse models of Alzheimer disease: developing a better model as a tool for therapeutic interventions

Alzheimer disease (AD) is the leading cause of dementia among elderly. Currently, no effective treatment is available for AD. Analysis of transgenic mouse models of AD has facilitated our understanding of disease mechanisms and provided valuable tools for evaluating potential therapeutic strategies. In this review, we will discuss the strengths and weaknesses of current mouse models of AD and the contribution towards understanding the pathological mechanisms and developing effective therapies.

Val97Leu mutant presenilin-1 induces tau hyperphosphorylation and spatial memory deficit in mice and the underlying mechanisms

Although the pathological role of presenilin-1 mutation in early onset familial Alzheimer's disease has been widely studied, few focused on how the presenilin-1 mutations result in memory impairment and tau hyperphosphorylation. In the present study, we expressed human Val97Leu mutant presenilin-1, which is reported in Chinese pedigrees by our group, in transgenic mice and found that the mutant presenilin-1 induced spatial memory deficit and tau hyperphosphorylation at PHF-1, pS199/202, pT231 and pS396 epitopes, but not at pS214 and pS422 epitopes. Pearson analysis showed that the memory deficit was only significantly correlated with tau phosphorylation level at PHF-1, pS199/202, pT231 and pS396 epitopes. Additionally, the hyperphosphorylated tau and tangle-like argentophilic structures were detected at CA3 and CA4, but not CA1, region of hippocampus, and we also found tangle-like structure and wizened degenerative neurons in frontal cortex. We demonstrated the tau hyperphosphorylation at the same epitopes in N2a cells expressing the mutant presenilin-1, which is caused by inhibition of phosphoinositol-3 kinase/Akt and activation of glycogen synthase kinase-3 specifically. Our data demonstrated that human Val97Leu mutant presenilin-1 causes spatial memory deficit in mice and increases tau phosphorylation level in glycogen synthase kinase-3-dependent manner.

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.

Worldwide distribution of PSEN1 Met146Leu mutation: a large variability for a founder mutation

OBJECTIVE

Large kindreds segregating familial Alzheimer disease (FAD) offer the opportunity of studying clinical variability as observed for presenilin 1 (PSEN1) mutations. Two early-onset FAD (EOFAD) Calabrian families with PSEN1 Met146Leu (ATG/CTG) mutation constitute a unique population descending from a remote common ancestor. Recently, several other EOFAD families with the same mutation have been described worldwide.

METHODS

We searched for a common founder of the PSEN1 Met146Leu mutation in families with different geographic origins by genealogic and molecular analyses. We also investigated the phenotypic variability at onset in a group of 50 patients (mean age at onset 40.0 +/- 4.8 years) by clinical, neuropsychological, and molecular methodologies.

RESULTS

EOFAD Met146Leu families from around the world resulted to be related and constitute a single kindred originating from Southern Italy before the 17th century. Phenotypic variability at onset is broad: 4 different clinical presentations may be recognized, 2 classic for AD (memory deficits and spatial and temporal disorientation), whereas the others are expressions of frontal impairment. The apathetic and dysexecutive subgroups could be related to orbital-medial prefrontal cortex and dorsolateral prefrontal cortex dysfunction.

CONCLUSIONS

Genealogic and molecular findings provided evidence that the PSEN1 Met146Leu families from around the world analyzed in this study are related and represent a single kindred originating from Southern Italy. The marked phenotypic variability might reflect early involvement by the pathologic process of different cortical areas. Although the clinical phenotype is quite variable, the neuropathologic and biochemical characteristics of the lesions account for neurodegenerative processes unmistakably of Alzheimer nature.

Review: Recent progress in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a highly familial condition and is increasingly being recognized as an important form of dementia. The literature published on this disease is often difficult to collate due to the wide range in nomenclature used. Thankfully, consensus recommendations have now been published to address this issue and hopefully the community will adopt these as intended. Much progress has been made in our understanding of the clinical, pathological and genetic understanding of FTLD in recent years. Progranulin and TDP-43 have recently been identified as new important proteins involved in the pathophysiology of FTLD and this latter protein may have potential as a biomarker of this disease. However, much remains before we have a full picture of the genes that cause FTLD and the biological pathways in which they function. The purpose of this review is to summarize the current concepts and recent advances in our knowledge of this disease.

APOE-4 genotype and neurophysiological vulnerability to Alzheimer's and cognitive aging

Many years before receiving a clinical diagnosis of Alzheimer's disease (AD), patients experience evidence of cognitive decline. Recent studies using a variety of brain imaging technologies have detected subtle changes in brain structure and function in normal adults with a genetic risk for AD; these brain changes have similar pathological features as AD, and some appear to be predictive of future cognitive decline. This review examines the most recent data on brain changes in genetic risk for AD and discusses the benefits and potential risks of detecting individuals at risk.

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.

Novel PSEN1 and PGRN mutations in early-onset familial frontotemporal dementia

BACKGROUND

Frontotemporal dementia is a clinically and genetically heterogeneous syndrome. Mutations in two genes, Microtubule Associated Protein Tau (MAPT) and Progranulin (PGRN), and rarely Presenilin mutations, have been causally linked to this disorder.

OBJECTIVE

To investigate the presence of PGRN, PSEN1, PSEN2 and APP mutations in a group of familial early-onset frontotemporal dementia (f-EOFTD) patients negative for MAPT gene mutations.

SUBJECTS AND METHODS

We prospectively studied 17 unrelated subjects diagnosed with f-EOFTD (one case neuropathologically confirmed as FTD-Ub+). Among these subjects eight belonged to eight autosomal dominant families unrelated to each other, and nine had at least one first degree relative affected by dementia.

RESULTS

We identified two novel heterozygous mutations in two unrelated patients, Cys139Arg in the PGRN gene and Val412Ile in the PSEN1 gene.

CONCLUSIONS

Early-onset f-FTD remains a heterogeneous disorder from a genetic point of view. PGRN mutation frequency was low in our sample. The presence of a novel PSEN1 mutation suggests that presenilin molecular studies should be performed when screening for MAPT and PGRN genes is negative.

Relative hyperperfusion by SPECT in a family with a presenilin 1 (T245P) mutation

Clinical characteristics of autosomal dominant Alzheimer's disease often differ clinically from sporadic disease with the onset of seizures, spasticity and myoclonus early in the disease course. Similarly imaging characteristics may also differ. We report the findings of relative hyperperfusion by Tc-99m HMPAO SPECT in the medial orbitofrontal cortex and anterior temporal lobe in four affected family members carrying a presenilin 1 mutation. SPECT of the four individuals was compared to an age-matched normal database. We speculate that the findings of relative medial orbitofrontal and anterior temporal lobe hyperperfusion may be a marker of early onset Alzheimer's disease in this family.

Decreased cerebrospinal fluid amyloid beta (1-40) levels in frontotemporal lobar degeneration

The role of amyloid metabolism in the pathophysiology of frontotemporal lobar degeneration (FTLD) has yet to be elucidated. We compared CSF levels of amyloid beta 1-40 (Abeta40) and amyloid beta 1-42 (Abeta42) in patients with FTLD (n = 21) versus patients with Alzheimer's disease (AD, n = 39) and in control subjects (n = 30). While in AD cases Abeta42 levels were lower and CSF Abeta40 levels equal to those in controls, a significant decrease in Abeta40 and increase in the CSF Abeta42/Abeta40 ratio was observed in FTLD compared with AD and control subjects. These findings favour a differential involvement of amyloid beta peptides in FTLD compared with AD.

Neuropathologic heterogeneity in HDDD1: a familial frontotemporal lobar degeneration with ubiquitin-positive inclusions and progranulin mutation

Hereditary dysphasic disinhibition dementia (HDDD) describes a familial disorder characterized by personality changes, and language and memory deficits. The neuropathology includes frontotemporal lobar atrophy, neuronal loss and gliosis and, in most cases, abundant Abeta plaques and neurofibrillary tangles (NFTs). A Pick/Alzheimer's spectrum was proposed for the original family (HDDD1). Here we report the clinicopathologic case of an HDDD1 individual using modern immunohistochemical methods, contemporary neuropathologic diagnostic criteria to distinguish different frontotemporal lobar degenerations (FTLDs), and progranulin (PRGN) mutation analysis. Clinical onset was at age 62 years with personality changes and disinhibition, followed by nonfluent dysphasia, and memory loss that progressed to muteness and total dependence with death at age 84 years. There was severe generalized brain atrophy (weight=570 g). Histopathology showed superficial microvacuolation, marked neuronal loss, gliosis, and ubiquitin-positive, tau-negative cytoplasmic and intranuclear neuronal inclusions in frontal, temporal, and parietal cortices. There were also frequent neuritic plaques and NFTs in parietal and occipital cortices. The case met neuropathologic criteria for both FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U), and Alzheimer disease (Braak NFT stage V). We discovered a novel pathogenic PGRN mutation c.5913 A>G (IVS6-2 A>G) segregating with FTLD-U in this kindred. In conclusion, HDDD1 is an FTLD-U caused by a PGRN mutation and is neuropathologically heterogeneous with Alzheimer disease as a common comorbidity.

Presenilin dependence of phospholipase C and protein kinase C signaling

Presenilins (PSs) are involved in processing several proteins such as the amyloid precursor protein (APP), as well as in pathways for cell death and survival. We previously showed that some familial Alzheimer's disease PS mutations cause increased basal and acetylcholine muscarinic receptor-stimulated phospholipase C (PLC) activity which was gamma-secretase dependent. To further evaluate the dependence of PLC on PSs we measured PLC activity and the activation of variant protein kinase C (PKC) isoforms in mouse embryonic fibroblasts (MEFs) lacking either PS1, PS2, or both. PLC activity and PKCalpha and PKCgamma activations were significantly lower in PS1 and PS2 double knockout MEFs after PLC stimulation. Protein levels of PKCalpha and PKCgamma were lower in PS1 and PS2 double knockout MEFs. In contrast, PKCdelta levels were significantly elevated in PS1 and PS2 double knockout as well as in PS1 knockout MEFs. Also, PKCdelta levels were lowered after transfection of PS1 into PS1 knockout or PS double knockout MEFs. Using APP knockout MEFs we showed that the expression of PKCalpha, but not the other PKC isoforms is partially dependent on APP and can be regulated by APP intracellular domain (AICD). These results show that PLC and PKC activations are modulated by PS and also that PSs differentially regulate the expression of PKC isoforms by both APP/AICD-dependent and independent mechanisms.

Familial Alzheimer disease-linked mutations specifically disrupt Ca2+ leak function of presenilin 1

Mutations in presenilins are responsible for approximately 40% of all early-onset familial Alzheimer disease (FAD) cases in which a genetic cause has been identified. In addition, a number of mutations in presenilin-1 (PS1) have been suggested to be associated with the occurrence of frontal temporal dementia (FTD). Presenilins are highly conserved transmembrane proteins that support cleavage of the amyloid precursor protein by gamma-secretase. Recently, we discovered that presenilins also function as passive ER Ca(2+) leak channels. Here we used planar lipid bilayer reconstitution assays and Ca(2+) imaging experiments with presenilin-null mouse embryonic fibroblasts to analyze ER Ca(2+) leak function of 6 FAD-linked PS1 mutants and 3 known FTD-associated PS1 mutants. We discovered that L166P, A246E, E273A, G384A, and P436Q FAD mutations in PS1 abolished ER Ca(2+) leak function of PS1. In contrast, A79V FAD mutation or FTD-associated mutations (L113P, G183V, and Rins352) did not appear to affect ER Ca(2+) leak function of PS1 in our experiments. We validated our findings in Ca(2+) imaging experiments with primary fibroblasts obtained from an FAD patient possessing mutant PS1-A246E. Our results indicate that many FAD mutations in presenilins are loss-of-function mutations affecting ER Ca(2+) leak activity. In contrast, none of the FTD-associated mutations affected ER Ca(2+) leak function of PS1, indicating that the observed effects are disease specific. Our observations are consistent with the potential role of disturbed Ca(2+) homeostasis in Alzheimer disease pathogenesis.

The complex aetiology of frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is now a widely recognised form of dementia. This heterogeneous disease has been of particular interest to geneticists due to its high rate of heritability with up to 40% of patients reporting a family history of the disease in at least one extra family member. There have been several chromosome loci linked to this disorder and three genes have already been identified. Remarkably, it has been recently demonstrated that 2 of these are only 1.7 Mb from one another on chromosome 17q21, these being tau and progranulin. The identification of these genes has contributed greatly to our understanding of the differing neuropathologies associated with FTLD. Furthermore, the discovery that TDP-43 is a component of the neuronal inclusions seen in the most common neuropathological subtype has also helped expand the biochemical pathways that are the focus of much FTLD research. Nevertheless, other genes causing FTLD remain to be identified and their biology elucidated before we have a complete understanding of the complex aetiology of this disease.

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.

Two novel presenilin 1 gene mutations connected with frontotemporal dementia-like clinical phenotype: Genetic and bioinformatic assessment

Mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes are associated with early-onset familial Alzheimer's disease (EOAD). There are several reports describing mutations in PSEN1 in cases with frontotemporal dementia (FTD). We identified two novel mutations in the PSEN1 gene: L226F and L424H. The first mutation was detected in a patient with a clinical diagnosis of FTD and a post-mortem diagnosis of AD. The second mutation is connected with a clinical phenotype of variant AD with strong FTD signs. In silico modeling revealed that the mutations, as well as mutations used for comparison (F177L and L424R), change the local structure, stability and/or properties of the transmembrane regions of the presenilin 1 protein (PS1). In contrast, a silent non-synonymous substitution F175S is eclipsed by external residues and has no influence on PS1 interfacial surface. We suggest that in silico analysis of PS1 substitutions can be used to characterize novel PSEN1 mutations, to discriminate between silent polymorphisms and a potential disease-causing mutation. We also propose that PSEN1 mutations should be considered in FTD patients with no MAPT mutations.

Pathological and physiological functions of presenilins

Mutations in PSEN1 and PSEN2 genes account for the majority of cases of early-onset familial Alzheimer disease. Since the first prediction of a genetic link between PSEN1 and PSEN2 with Alzheimer's disease, many research groups from both academia and pharmaceutical industry have sought to unravel how pathogenic mutations in PSEN cause presenile dementia. PSEN genes encode polytopic membrane proteins termed presenilins (PS1 and PS2), which function as the catalytic subunit of γ-secretase, an intramembrane protease that has a wide spectrum of type I membrane protein substrates. Sequential cleavage of amyloid precursor protein by BACE and γ-secretase releases highly fibrillogenic β-amyloid peptides, which accumulate in the brains of aged individuals and patients with Alzheimer's disease. Familial Alzheimer's disease-associated presenilin variants are thought to exert their pathogenic function by selectively elevating the levels of highly amyloidogenic Aβ42 peptides. In addition to Alzheimer's disease, several recent studies have linked PSEN1 to familiar frontotemporal dementia. Here, we review the biology of PS1, its role in γ-secretase activity, and discuss recent developments in the cell biology of PS1 with respect to Alzheimer's disease pathogenesis.

Frontotemporal dementia—A brief review

Frontotemporal dementia (FTD) is the second most common type of presenile dementia and the forth most common type of senile dementia, but probably the most costly due to its florid symptom characteristics. Clinically, it often presents with changes of personality, restlessness, disinhibition, and impulsiveness and the clinical features can be complicated by neurological signs, such as motor neuron signs, parkinsonism, and gait disturbances. Syndromatically, FTD can be subdivided into a group with predominating behavioural disturbances (frontal variant) and another with predominating language deterioration (temporal variant). Based on the underlying pathological changes, FTD is nosologically divided into disorders such as Pick's disease, frontotemporal lobar degeneration, corticobasal degeneration, progressive supranuclear palsy, and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). The cause in sporadic FTD is most often unknown, but in FTDP-17, one of the hereditary FTDs, there is a causative mutation in the tau gene. The frequency of tau-gene mutations is low in sporadic FTD and present in about 10-40% of hereditary FTD. Other types of hereditary FTD have been described, such as FTD caused by mutations in chromosome 3, chromosome 9, and a FTD syndrome can also be caused by mutations in the presenilin-1 gene. Since there is no curative, treatment of prevailing symptoms is the given alternative. Serotonergic acting drugs have been shown to alleviate behavioural symptoms.

Formation of tau inclusions in knock-in mice with familial Alzheimer disease (FAD) mutation of presenilin 1 (PS1)

Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheimer disease (FAD). Accumulating evidence shows that PS1 is involved in gamma-secretase activity and that FAD-associated mutations of PS1 commonly accelerate Abeta(1-42) production, which causes Alzheimer disease (AD). Recent studies suggest, however, that PS1 is involved not only in Abeta production but also in other processes that lead to neurodegeneration. To better understand the causes of neurodegeneration linked to the PS1 mutation, we analyzed the development of tau pathology, another key feature of AD, in PS1 knock-in mice. Hippocampal samples taken from FAD mutant (I213T) PS1 knock-in mice contained hyperphosphorylated tau that reacted with various phosphodependent tau antibodies and with Alz50, which recognizes the conformational change of PHF tau. Some neurons exhibited Congo red birefringence and Thioflavin T reactivity, both of which are histological criteria for neurofibrillary tangles (NFTs). Biochemical analysis of the samples revealed SDS-insoluble tau, which under electron microscopy examination, resembled tau fibrils. These results indicate that our mutant PS1 knock-in mice exhibited NFT-like tau pathology in the absence of Abeta deposition, suggesting that PS1 mutations contribute to the onset of AD not only by enhancing Abeta(1-42) production but by also accelerating the formation and accumulation of filamentous tau.

Tau is central in the genetic Alzheimer–frontotemporal dementia spectrum

In contrast to the common and genetically complex senile form of Alzheimer's disease (AD), the molecular genetic dissection of inherited presenile dementias has given important mechanistic insights into the pathogenesis of degenerative brain disease. Here, we focus on recent genotype-phenotype correlative studies in presenile AD and the frontotemporal dementia (FTD) complex of disorders. Together, these studies suggest that AD and FTD are linked in a genetic spectrum of presenile degenerative brain disorders in which tau appears to be the central player.

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.

"Frontal variant Alzheimer's disease": a reappraisal

Two cases of clinically diagnosed sporadic Alzheimer's disease with early and prominent behavioural features (social disinhibition, emotional blunting, stereotyped verbal utterances) sufficient to prompt an initial diagnosis of frontotemporal dementia are presented. It is suggested that the term "frontal variant AD" be used for this clinically defined phenotype, which has also been described in cases of inherited AD associated with certain presenilin-1 gene mutations. This differs from previous usage of the term "frontal variant AD" to describe AD with predominant frontal lobe neuropathological change (although the clinical phenotype may reflect regional distribution of pathology), but parallels the clinical definition of visual agnosic, aphasic and apraxic presentations of AD. The proposed usage would also emphasise differential diagnosis.

Presenilins mediate phosphatidylinositol 3-kinase/AKT and ERK activation via select signaling receptors. Selectivity of PS2 in platelet-derived growth factor signaling

The Alzheimer's disease-linked genes, PS1 and PS2, are required for intramembrane proteolysis of multiple type I proteins, including Notch and amyloid precursor protein. In addition, it has been documented that PS1 positively regulates, whereas PS1 familial Alzheimer disease mutations suppress, phosphatidylinositol 3-kinase (PI3K)/Akt activation, a pathway known to inactivate glycogen synthase kinase-3 and reduce tau phosphorylation. In this study, we show that the loss of presenilins not only inhibits PI3K/Akt signaling and increases tau phosphorylation but also suppresses the MEK/ERK pathway. The deficits in Akt and ERK activation in cells deficient in both PS1 and PS2 (PS-/-) are evident after serum withdrawal and stimulation with fetal bovine serum or ligands of select receptor tyrosine kinases, platelet-derived growth factor receptor beta (PDGFR beta) and PDGFR alpha, but not insulin-like growth factor-1R and epidermal growth factor receptor. The defects in PDGF signaling in PS-/- cells are due to reduced expression of PDGF receptors. Whereas fetal bovine serum-induced Akt activation is reconstituted by both PS1 and PS2 in PS-/- cells, PDGF signaling is selectively restored by PS2 but not PS1 and is dependent on the N-terminal fragment of PS2 but not gamma-secretase activity or the hydrophilic loop of PS2. The rescue of PDGF receptor expression and activation by PS2 is facilitated by FHL2, a PS2-interacting transcriptional co-activator. Finally, we present evidence that PS1 mutations interfere with this PS2-mediated activity by reducing PS2 fragments. These findings highlight important roles of both presenilins in Akt and ERK signaling via select signaling receptors.

Hypersexuality and dysexecutive syndrome after a thalamic infarct

Hypersexuality can result from insults to several neuroanatomical structures that regulate sexual behavior. A case is presented of an adult male with a thalamic infarct resulting in a paramedian thalamic syndrome, consisting of hypersomnolence, confabulatory anterograde amnesia (including reduplicative paramnesia), vertical gaze deficits, and hypophonic speech. A dysexecutive syndrome also manifested, consisting of social disinhibition, apathy, witzelsucht, motor inhibition deficits, and environmental dependence. Hypersexuality uncharacteristic of his premorbid behavior was evident in instances of exhibitionism, public masturbation, and verbal sexual obscenities. In contrast to the few previous reports of hypersexuality following thalamic infarct, this case neither involved mania nor hemichorea. The relevance of the mediodorsal thalamic nucleus in limbic and prefrontal circuits is discussed.

A novel presenilin 1 mutation associated with Pick's disease but not beta-amyloid plaques

Familial forms of frontotemporal dementia (FTD) with tauopathy are mostly caused by mutations in the gene encoding the microtubule-associated protein tau (MAPT). However, rare forms of familial tauopathy without MAPT mutations have been reported, suggesting other tauopathy-related genetic defects. Interestingly, two presenilin 1 (PS1) mutations (Leu113Pro and insArg352) recently have been associated with familial FTD albeit without neuropathological confirmation. We report here a novel PS1 mutation in a patient with Pick-type tauopathy in the absence of extracellular beta-amyloid deposits. The mutation is predicted to substitute Gly-->Val at codon position 183 (Gly183Val) and to affect the splice signal at the junction of the sixth exon and intron. Further clinical-genetic investigation showed a positive family history of FTD-like dementia and suggested that Gly183Val is associated with a phenotypically heterogeneous neurodegenerative disorder. Our results suggest PS1 as a candidate gene for Pick-type tauopathy without MAPT mutations.

Atypical dementia associated with a novel presenilin-2 mutation

We describe an Italian pedigree with hereditary dementia associated with a novel T122R mutation in the presenilin-2 gene (PSEN2). The clinical history, symptom presentation, and structural neuroimaging were consistent with an atypical form of dementia. Disease expression varied within family members. One in a pair of mutated monozygotic twins had evident signs of disease, whereas the other did not, even if her functional neuroimaging investigations, cerebrospinal fluid levels of Abeta1-42, and Tau protein were able to provide markers for future disease development. These observations suggest the importance of still unknown biological and perhaps environmental factors in the disease determination.