Clinical phenotypes and genetic biomarkers of FTLD

Frontotemporal lobar degeneration (FTLD) is the most frequent neurodegenerative disorder with a presenile onset. It presents with a spectrum of clinical manifestations, ranging from behavioural and executive impairment to language disorders and motor dysfunction. New diagnostic criteria identified two main cognitive syndromes: behavioural variant frontotemporal dementia (bvFTD) and primary progressive aphasia (PPA). Regarding bvFTD, new criteria that include the use of biomarkers have been proposed. According to them, bvFTD can be classified in "possible" (clinical features only), "probable" (inclusion of imaging biomarkers) and "definite" (in the presence o f a known causal mutation or at autopsy). Concerning autosomal dominant mutations, microtubule associated protein tau gene mutations have been the first ones identified and are generally associated with early onset bvFTD phenotype. More recently, progranulin gene mutations were recognized in association with familial form of FTLD. In addition, other genes are linked to rare cases of familial FTLD, primarily the newly discovered C9ORF72 hexanucleotide expansion repeats. As regards PPA, new consensus criteria identify three syndromes: primary non-fluent aphasia, semantic variant of PPA and logopenic aphasia, which seems to be associated, in the majority of cases, with underlying Alzheimer's disease pathology. In this review, new criteria, including MRI, cerebrospinal fluid and genetic biomarkers, will be presented and discussed.     

The behavioral variant of frontotemporal dementia: linking neuropathology to social cognition

The behavioral variant of frontotemporal dementia (bvFTD) is one of the most frequent neurodegenerative disorders with a presenile onset. It is characterized by a long phase of subclinical behavioral changes and social conduct disorders, associated with a progressive modification of personality. Recently, an international consortium of experts developed revised guidelines for its clinical diagnosis, which highlight the supportive role of biomarkers in the diagnostic process. According to new criteria, bvFTD can be classified in “possible” (requiring three of six specific clinical features), “probable” (in the presence of functional disability and typical neuroimaging features), and “with definite frontotemporal lobar degeneration” (requiring the presence of a known causal mutation or a histopathological confirmation). Familial aggregation is frequently reported in bvFTD and frontotemporal lobar degeneration in general, with an autosomal dominant transmission in about 10 % cases. The aim of this paper is to review and discuss recent advances in the knowledge of clinical, neuropsychological, and imaging features of bvFTD. We also briefly summarize the available genetic information about the frontotemporal lobar degeneration spectrum.     

Estimating the Number of Persons with Frontotemporal Lobar Degeneration in the US Population

There are many challenges for determining the prevalence and incidence of frontotemporal lobar degenerations (FTLD). Consequently, the number of cases of behavioral variant frontotemporal dementia (bvFTD) or primary progressive aphasia (PPA) in the USA is unknown. Our objective was to derive a consensus estimate of bvFTD and PPA prevalence and thereby to estimate the total number of these syndromes in the USA. We identified five prevalence and three incidence studies of FTLD based on passive surveillance and seven studies of survival in FTLD. Data from these studies were used to estimate the number of cases of PPA or bvFTD in the USA. Because prevalence and incidence estimates outside of the 45–64-year age range were either not available or widely divergent, we used data from clinical and pathological series to estimate the proportion of FTLD cases aged <45 or >64 years. The prevalence estimates in the age categories of 45–64 years old have ranged from 15 to 22 per 100,000 person-years in studies where both bvFTD and PPA were identified. The incidence estimates for the same age group ranged from 2.7 to 4.1 per 100,000 person-years. Using a survival rate of 6 to 9 years from onset and rates from the incidence studies, a calculated prevalence estimate (prevalence = incidence × duration) was similar to the previously reported prevalence rates. We estimated that 10% of cases were less than age 45 years and 30% were 65 years and older. We estimate that there are approximately 20,000 to 30,000 cases of the cognitive syndromes of FTLD in the USA. The main threat to the accuracy of the estimates is the difficulty in diagnosing the clinical syndromes that comprise the FTLD group of disorders.     

FUS mutations in frontotemporal lobar degeneration with amyotrophic lateral sclerosis

Rapid advances were made in the knowledge of amyotrophic lateral sclerosis (ALS) with the recent identification of TARDBP and FUS mutations in familial ALS. More recently, FUS-positive inclusions were found in a subset of TDP-43-negative frontotemporal lobar degeneration (FTLD) prompting us to analyze FUS in FTLD and FTLD-ALS patients. The p.Arg521His mutation was identified in a patient who initially had behavioral disorders and rapidly developed ALS. Although the frequency of mutations is low, our study enlarges the phenotypes associated with FUS mutations and shows that FUS could also play a direct pathogenic role in FTLD spectrum of diseases.     

Frontotemporal lobar degeneration: Diversity of FTLD lesions

Frontotemporal lobar degeneration (FTLD) is a heterogeneous group including both sporadic and familial diseases, characterized by a macroscopic alteration. It may correspond to various cognitive syndromes: behavioral variant of frontotemporal dementia (bvFTD), progressive nonfluent aphasia, and semantic dementia. The neuropathologic classification is now based on identification of the protein that accumulates in neurons and glia: Tau, TAR DNA Binding Protein 43 (TDP-43), and FUsed in Sarcoma (FUS). The disorders in which the corresponding proteins accumulate have been named FTLD-Tau, FTLD-TDP, and FTLD-FUS. FTLD-Tau includes sporadic cases (e.g. Pick's disease) and Tau mutations. FTLD-TDP are subdivided within four types (A, B, C, D) according to the shape and distribution of TDP-43 positive lesions within the associative frontal cortex. The FTLD-FUS group includes atypical FTLD with ubiquitinated lesions (FTLD-U), Neuronal Intermediate Filament Inclusion Disease (NIFID) and Basophilic Inclusion Body Disease (BIBD).     

Behavioral variant of frontotemporal dementia: Fundamental clinical issues associated with prediction of pathological bases

Behavioral variant of frontotemporal dementia (bvFTD) is a clinical syndrome characterized mainly by behavioral symptoms due to frontal dysfunction. Major neurodegenerative bases of bvFTD include Pick's disease, frontotemporal lobar degeneration with trans‐activation response DNA protein 43‐positive inclusions, corticobasal degeneration, and progressive supranuclear palsy. Early disinhibition characterized by socially inappropriate behaviors, loss of manners, and impulsive, rash and careless actions is the most important clinical feature of bvFTD. On the other hand, it was reported that clinical presentations of some Alzheimer's disease cases and patients with psychiatric disorders (e.g., addictive disorders, gambling disorder and kleptomania) often resemble that of bvFTD. Although clinical differentiation of ‘true’ bvFTD cases with frontotemporal lobar degeneration (FTLD) pathology from mimicking cases without it is not always easy, evaluation of the following features, which were noted in autopsy‐confirmed FTLD cases and/or clinical bvFTD cases with circumscribed lobar atrophy, may often provide clues for the diagnosis. (i) The initial symptoms frequently develop at 65 years or younger, and (ii) ‘socially inappropriate behaviors’ can be frequently interpreted as contextually inappropriate behaviors prompted by environmental visual and auditory stimuli. Taking a detailed history usually reveals various kinds of such behaviors in various situations in everyday life rather than the repetition of a single kind of behavior (e.g., repeated shoplifting). (iii) A correlation between the distribution of cerebral atrophy and neurological and behavioral symptoms is usually observed, and the proportion of FTLD cases with right side‐predominant cerebral atrophy may be higher in a psychiatric setting than a neurological setting. Finally, (iv) whether the previous course and the combination of symptoms observed at the first medical visit can be explained by major evolution patterns of clinical syndromes in pathologically confirmed FTLD cases should be considered. These views may provide clues to differentiate FTLD from Alzheimer's disease and to predict a subsequent clinical course and therapeutic interventions needed in the future.     

Neuropathological background of phenotypical variability in frontotemporal dementia

Frontotemporal lobar degeneration (FTLD) is the umbrella term encompassing a heterogeneous group of pathological disorders. With recent discoveries, the FTLDs have been show to classify nicely into three main groups based on the major protein deposited in the brain: FTLD-tau, FTLD-TDP and FTLD-FUS. These pathological groups, and their specific pathologies, underlie a number of well-defined clinical syndromes, including three frontotemporal dementia (FTD) variants [behavioral variant frontotemporal dementia (bvFTD), progressive non-fluent aphasia, and semantic dementia (SD)], progressive supranuclear palsy syndrome (PSPS) and corticobasal syndrome (CBS). Understanding the neuropathological background of the phenotypic variability in FTD, PSPS and CBS requires large clinicopathological studies. We review current knowledge on the relationship between the FTLD pathologies and clinical syndromes, and pool data from a number of large clinicopathological studies that collectively provide data on 544 cases. Strong relationships were identified as follows: FTD with motor neuron disease and FTLD-TDP; SD and FTLD-TDP; PSPS and FTLD-tau; and CBS and FTLD-tau. However, the relationship between some of these clinical diagnoses and specific pathologies is not so clear cut. In addition, the clinical diagnosis of bvFTD does not have a strong relationship to any FTLD subtype or specific pathology and therefore remains a diagnostic challenge. Some evidence suggests improved clinicopathological association of bvFTD by further refining clinical characteristics. Unlike FTLD-tau and FTLD-TDP, FTLD-FUS has been less well characterized, with only 69 cases reported. However, there appears to be some associations between clinical phenotypes and FTLD-FUS pathologies. Clinical diagnosis is therefore promising in predicting molecular pathology.     

Genetics of frontotemporal lobar degeneration: An up-date and diagnosis algorithm

The last decade marked a turning point in the knowledge of frontotemporal lobar degenerations (FTLD). Major discoveries were made with the identification of TDP-43 and FUS, two novel key players in FTLD. The growing number of FTLD genes has considerably changed our clinical practice. The high intrafamilial variability of phenotypes underlines the necessity of a careful interview concerning the family history, regarding FTLD diseases, but also other neurodegenerative and extra-neurological disorders. Knowledge of the different genetic forms of FTLD and their associated phenotypes become essential to propose appropriate genetic diagnosis to the patients, and deliver accurate genetic counseling to their families. We propose an algorithm based on four criteria to help to pinpoint the genetic cause of FTLD: Presence of ALS in the patient or family; age at onset of FTLD; progranulin plasma level; and other disorders present in the patient or family. Presence of ALS is strongly indicative of a C9ORF72 expansion; a very early age at onset (< 50 years), parkinsonism and oculomotor dysfunction are indicative of MAPT mutations; whereas hallucinations, CBDS and PNFA are indicative of PGRN mutations. A C9ORF72 repeat expansion should be searched for therefore in patients with FTLD-ALS, followed by sequencing of exon 6 of TARDBP gene in negative cases. Since C9ORF72 expansions are as frequent as PGRN mutations in patients with pure FTLD, both should be investigated, except in early familial FTLD (< 50) where MAPT mutations should be searched for first. VCP, SQSTM1 and hnRNPA2B1 gene-sequencing could be proposed in patients or families presenting ‘multisystem proteinopathy’. The genes currently identified explain 50–60% of familial forms of FTLD. The identification of new FTLD genes involved remains a major challenge to gain further insight into the pathology and even better clarify the classification of FTLD in the future.     

Progranulin Leu271LeufsX10 is one of the most common FTLD and CBS associated mutations worldwide

Mutations in the progranulin gene (PGRN) are a major cause of frontotemporal lobar degeneration (FTLD). Herein we estimated the contribution of the PGRN Leu271LeufsX10 mutation to FTLD and related disorders in the Brescia cohort. The PGRN Leu271LeufsX10 mutation was found in 31% of corticobasal syndrome (CBS), 29% of frontotemporal dementia with motorneuron disease (FTD-MND), 15% of behavioral variant frontotemporal dementia (FTD), 9.5% of primary progressive aphasia (PPA), 2% dementia with Lewy bodies and 0% of progressive supranuclear palsy and multiple system atrophy cases. The prevalence strongly increased in familial forms (75% CBS, 50% FTD-MND, 27% FTD, 18% PPA): in our cohort this mutation is a major disease determinant for FTLD-related disorders with a prominent motor component. MAPT haplotype was demonstrated to be a disease modifier in PGRN Leu271LeufsX10 carriers: in H1H2 subjects the disease onset was earlier than in H2H2 individuals. Sequencing of the whole PGRN gene disclosed a previously described mutation (c.2T > C, Met1X) and three novel ones (c.709-3; c.1011delG, His340ThrfsX21; c.1021C > T, Gln341X) in single families. In the Brescia cohort, while MAPT mutations have low prevalence, mutations in PGRN were shown in 28% of familial FTLD and 75% of familial CBS cases. The PGRN Leu271LeufsX10 mutation becomes one of the most common mutations worldwide, since it was identified in 38 patients belonging to 27 unrelated families.     

Contribution of CSF biomarkers to early‐onset Alzheimer's disease and frontotemporal dementia neuroimaging signatures

Prior studies have described distinct patterns of brain gray matter and white matter alterations in Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD), as well as differences in their cerebrospinal fluid (CSF) biomarkers profiles. We aim to investigate the relationship between early‐onset AD (EOAD) and FTLD structural alterations and CSF biomarker levels. We included 138 subjects (64 EOAD, 26 FTLD, and 48 controls), all of them with a 3T MRI brain scan and CSF biomarkers available (the 42 amino acid‐long form of the amyloid‐beta protein [Aβ42], total‐tau protein [T‐tau], neurofilament light chain [NfL], neurogranin [Ng], and 14‐3‐3 levels). We used FreeSurfer and FSL to obtain cortical thickness (CTh) and fraction anisotropy (FA) maps. We studied group differences in CTh and FA and described the “AD signature” and “FTLD signature.” We tested multiple regression models to find which CSF‐biomarkers better explained each disease neuroimaging signature. CTh and FA maps corresponding to the AD and FTLD signatures were in accordance with previous literature. Multiple regression analyses showed that the biomarkers that better explained CTh values within the AD signature were Aβ and 14‐3‐3; whereas NfL and 14‐3‐3 levels explained CTh values within the FTLD signature. Similarly, NfL levels explained FA values in the FTLD signature. Ng levels were not predictive in any of the models. Biochemical markers contribute differently to structural (CTh and FA) changes typical of AD and FTLD.     

ALS and FTLD: two faces of TDP-43 proteinopathy

Major discoveries have been made in the recent past in the genetics, biochemistry and neuropathology of frontotemporal lobar degeneration (FTLD). TAR DNA-binding protein 43 (TDP-43), encoded by the TARDBP gene, has been identified as the major pathological protein of FTLD with ubiquitin-immunoreactive (ub-ir) inclusions (FTLD-U) with or without amyotrophic lateral sclerosis (ALS) and sporadic ALS. Recently, mutations in the TARDBP gene in familial and sporadic ALS have been reported which demonstrate that abnormal TDP-43 alone is sufficient to cause neurodegeneration. Several familial cases of FTLD-U, however, are now known to have mutations in the progranulin ( GRN ) gene, but granulin is not a component of the TDP-43- and ub-ir inclusions. Further, TDP-43 is found to be a component of the inclusions of an increasing number of neurodegenerative diseases. Other FTLD-U entities with TDP-43 proteinopathy include: FTLD-U with valosin-containing protein ( VCP ) gene mutation and FTLD with ALS linked to chromosome 9p. In contrast, chromosome 3-linked dementia, FTLD-U with chromatin modifying protein 2B ( CHMP2B ) mutation, has ub-ir, TDP-43-negative inclusions. In summary, recent discoveries have generated new insights into the pathogenesis of a spectrum of disorders called TDP-43 proteinopathies including: FTLD-U, FTLD-U with ALS, ALS, and a broadening spectrum of other disorders. It is anticipated that these discoveries and a revised nosology of FTLD will contribute toward an accurate diagnosis, and facilitate the development of new diagnostic tests and therapeutics.     

Frontotemporal lobar degeneration – tau as a pied piper?

Frontotemporal lobar degeneration (FTLD) is the second most-common form of cortical dementia in the presenium after Alzheimer disease. Clinically three disease entities can be distinguished: frontotemporal dementia, semantic dementia, and primary progressive aphasia. The underlying neuropathology can be classified into disorders with tau pathology (including Pick disease, corticobasal degeneration, progressive supranuclear palsy, and familial frontotemporal dementia with parkinsonism linked to chromosome 17 – FTDP-17), and into disorders that lack tau abnormalities (including dementia lacking distinctive histology and motor neuron disease inclusion dementia). The recent discovery of tau gene mutations in FTDP-17 brought tau to the center stage, but led to the erroneous trend of collectively grouping all forms of FTLD as tauopathies. However, clinicopathological and genetic studies strongly suggest that the majority of sporadic and familial FTLD cases are not associated with tau pathology and/or tau gene mutations. Furthermore, recent studies have linked several autosomal dominantly inherited familial frontotemporal dementia cases to a variety of gene loci on different chromosomes. Thus, this review is intended to summarize our current knowledge about the sporadic and familial FTLD disorders that lack tau pathology, and shall further strengthen the view that FTLD is heterogeneous, both in terms of clinicopathological phenotypes as well as genetic backgrounds. Electronic Publication     

Frontal variant of Alzheimer’s disease masquerading as behavioural-variant frontotemporal dementia: a case study comparison

The current clinical diagnostic criteria for Alzheimer’s disease (AD) recognize an atypical, non-amnestic presentation of AD, characterized by prominent executive dysfunction. Increasing evidence, however, indicates that the clinical phenotype of this so-called “frontal-variant” of AD (fv-AD) includes behavioral symptoms and deficits in social cognition, together with disproportionate frontal lobe atrophy. As these features resemble those characteristic of behavioral-variant frontotemporal dementia (bvFTD), differential diagnosis can be challenging. Here, we report a case of fv-AD who met clinical diagnostic criteria bvFTD, but had in vivo amyloid neuroimaging evidence of AD pathology. We compare this case against two individuals who were clinically diagnosed with bvFTD and early-onset AD, with in vivo amyloid neuroimaging confirmation of pathology. We highlight the challenges in differential diagnosis by contrasting their behavioral, cognitive and structural neuroimaging findings.     

Neuropathologic diagnostic and nosologic criteria for frontotemporal lobar degeneration: consensus of the Consortium for Frontotemporal Lobar Degeneration

The aim of this study was to improve the neuropathologic recognition and provide criteria for the pathological diagnosis in the neurodegenerative diseases grouped as frontotemporal lobar degeneration (FTLD); revised criteria are proposed. Recent advances in molecular genetics, biochemistry, and neuropathology of FTLD prompted the Midwest Consortium for Frontotemporal Lobar Degeneration and experts at other centers to review and revise the existing neuropathologic diagnostic criteria for FTLD. The proposed criteria for FTLD are based on existing criteria, which include the tauopathies [FTLD with Pick bodies, corticobasal degeneration, progressive supranuclear palsy, sporadic multiple system tauopathy with dementia, argyrophilic grain disease, neurofibrillary tangle dementia, and FTD with microtubule-associated tau (MAPT) gene mutation, also called FTD with parkinsonism linked to chromosome 17 (FTDP-17)]. The proposed criteria take into account new disease entities and include the novel molecular pathology, TDP-43 proteinopathy, now recognized to be the most frequent histological finding in FTLD. TDP-43 is a major component of the pathologic inclusions of most sporadic and familial cases of FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U) with or without motor neuron disease (MND). Molecular genetic studies of familial cases of FTLD-U have shown that mutations in the progranulin (PGRN) gene are a major genetic cause of FTLD-U. Mutations in valosin-containing protein (VCP) gene are present in rare familial forms of FTD, and some families with FTD and/or MND have been linked to chromosome 9p, and both are types of FTLD-U. Thus, familial TDP-43 proteinopathy is associated with defects in multiple genes, and molecular genetics is required in these cases to correctly identify the causative gene defect. In addition to genetic heterogeneity amongst the TDP-43 proteinopathies, there is also neuropathologic heterogeneity and there is a close relationship between genotype and FTLD-U subtype. In addition to these recent significant advances in the neuropathology of FTLD-U, novel FTLD entities have been further characterized, including neuronal intermediate filament inclusion disease. The proposed criteria incorporate up-to-date neuropathology of FTLD in the light of recent immunohistochemical, biochemical, and genetic advances. These criteria will be of value to the practicing neuropathologist and provide a foundation for clinical, clinico-pathologic, mechanistic studies and in vivo models of pathogenesis of FTLD.     

Clinical, neuropathological, and genetic characteristics of the novel IVS9+1delG GRN mutation in a patient with frontotemporal dementia

Frontotemporal lobar degeneration (FTLD) refers to a clinically, pathologically, and genetically heterogeneous group of dementias that arises from the degeneration of the frontal and temporal lobes. Mutations in the progranulin gene (GRN) are a major cause of FTLD with TDP-43 inclusions. Herein, we describe the clinical, neuropathological, and genetic findings in a case of autosomal dominant behavioral variant of frontotemporal dementia (bvFTD) with asymmetrical parkinsonism and prominent visuospatial deficits that carries a novel GRN mutation. This case highlights important clinical characteristics that seem to be common in FTLD GRN-associated patients, such as asymmetrical parkinsonism and parietal symptoms, and that are correlated to the pathological involvement of striatum (rather than substantia nigra in our case) and parietal lobe. We also emphasize that plasma progranulin level can be useful to infer about the pathogenicity of new GRN mutations.     

An immunohistochemical study of cases of sporadic and inherited frontotemporal lobar degeneration using 3R- and 4R-specific tau monoclonal antibodies

The pathological distinctions between the various clinical and pathological manifestations of frontotemporal lobar degeneration (FTLD) remain unclear. Using monoclonal antibodies specific for 3- and 4-repeat isoforms of the microtubule associated protein, tau (3R- and 4R-tau), we have performed an immunohistochemical study of the tau pathology present in 14 cases of sporadic forms of FTLD, 12 cases with Pick bodies and two cases without and in 27 cases of familial FTLD associated with 12 different mutations in the tau gene (MAPT), five cases with Pick bodies and 22 cases without. In all 12 cases of sporadic FTLD where Pick bodies were present, these contained only 3R-tau isoforms. Clinically, ten of these cases had frontotemporal dementia and two had progressive apraxia. Only 3R-tau isoforms were present in Pick bodies in those patients with familial FTLD associated with L266V, Q336R, E342V, K369I or G389R MAPT mutations. Patients with familial FTLD associated with exon 10 N279K, N296H or +16 splice site mutations showed tau pathology characterised by neuronal neurofibrillary tangles (NFT) and glial cell tangles that contained only 4R-tau isoforms, as did the NFT in P301L MAPT mutation. With the R406W mutation, NFT contained both 3R- and 4R-tau isoforms. We also observed two patients with sporadic FTLD, but without Pick bodies, in whom the tau pathology comprised only of 4R-tau isoforms. We have therefore shown by immunohistochemistry that different specific tau isoform compositions underlie the various kinds of tau pathology present in sporadic and familial FTLD. The use of such tau isoform specific antibodies may refine pathological criteria underpinning FTLD.     

Utility of clinical criteria in differentiating frontotemporal lobar degeneration (FTLD) from AD

OBJECTIVE: To assess the ability of the current diagnostic criteria for frontotemporal lobar degeneration (FTLD) to differentiate FTLD from AD. METHODS: Thirty cases with autopsy-proven FTLD and 30 cases of AD, matched for Mini-Mental State Examination score, were identified from the clinical databases of three dementia subspecialty centers, and their charts were reviewed for the presence of clinical features described in the current criteria for FTLD. The proportion of patients with each clinical feature at the first clinical presentation was compared across groups. RESULTS: A significantly larger proportion of patients with FTLD showed behavioral abnormalities, particularly social and personal conduct disorders and emotional blunting, than patients with AD. Few differences in language features were seen between the groups, and many of the language features detailed in the criteria were found in only a small proportion of patients. In both groups, many patients showed neuropsychological abnormalities, except for perceptual difficulties, which were present in many patients with AD but only in a few patients with FTLD. Extrapyramidal motor symptoms were more likely to be present in FTLD. Logistic regression revealed that five features-social conduct disorders, hyperorality, akinesia, absence of amnesia, and the absence of a perceptual disorder-correctly classified 93% of patients with FTLD and 97% of patients with AD. CONCLUSION: A combination of behavioral, neuropsychological, and physical findings is most useful in distinguishing FTLD from AD. Future studies should be directed at establishing more objective methods of identifying these clinical features.     

Molecular genetic analysis of the APP, PSEN1, and PSEN2 genes in Finnish patients with early-onset Alzheimer disease and frontotemporal lobar degeneration

Mutations in 3 genes, amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2), have been identified as causing a proportion of early-onset Alzheimer disease (eoAD) cases. A few PSEN mutations have also been previously detected in patients with frontotemporal lobar degeneration (FTLD). In order to evaluate the role of these genes in a clinical series of Finnish eoAD and FTLD patients, we sequenced exons 16 and 17 of the APP gene and the coding regions of the PSEN1 and PSEN2 genes in 140 eoAD and 66 FTLD patients. No pathogenic mutations were identified in the cohort. The E318G variant was detected with similar frequencies in the cases with eoAD and FTLD and the healthy controls, therefore, showing no association between E318G and eoAD. Furthermore, the PSEN2 R71W variant seems to be nonpathogenic, because it was present in our healthy controls. Mutations in the PSEN1, PSEN2, and APP genes seem to be rare in this population, as these genes exhibited no pathogenic mutations in our cohort of eoAD and FTLD patients even though about 40% of the cases were familial ones. This suggests the involvement of other, still unknown genetic factors in the pathogenesis of these diseases.