Ectopic white matter neurons, a developmental abnormality that may be caused by the PSEN1 S169L mutation in a case of familial AD with myoclonus and seizures

Strategies for modeling aging and age-related diseases

The ability to reprogram patient-derived-somatic cells to IPSCs (Induced Pluripotent Stem Cells) has led to a better understanding of aging and age-related diseases like Parkinson's, and Alzheimer's. The established patient-derived disease models mimic disease pathology and can be used to design drugs for aging and age-related diseases. However, the age and genetic mutations of the donor cells, the employed reprogramming, and the differentiation protocol might often pose challenges in establishing an appropriate disease model. In this review, we will focus on the various strategies for the successful reprogramming and differentiation of patient-derived cells to disease models for aging and age-related diseases, emphasizing the accuracy in the recapitulation of disease pathology and ways to overcome the limitations of its potential application in cell replacement therapy and drug development.

Familial cerebral amyloid disorders with prominent white matter involvement

Familial cerebral amyloid disorders are characterized by the accumulation of fibrillar protein aggregates, which deposit in the parenchyma as plaques and in the vasculature as cerebral amyloid angiopathy (CAA). Amyloid β (Aβ) is the most common of these amyloid proteins, accumulating in familial and sporadic forms of Alzheimer's disease and CAA. However, there are also a number of rare, hereditary, non-Aβ cerebral amyloidosis. The clinical manifestations of these familial cerebral amyloid disorders are diverse, including cognitive or neuropsychiatric presentations, intracerebral hemorrhage, seizures, myoclonus, headache, ataxia, and spasticity. Some mutations are associated with extensive white matter hyperintensities on imaging, which may or may not be accompanied by hemorrhagic imaging markers of CAA; others are associated with occipital calcification. We describe the clinical, imaging, and pathologic features of these disorders and discuss putative disease mechanisms. Familial disorders of cerebral amyloid accumulation offer unique insights into the contributions of vascular and parenchymal amyloid to pathogenesis and the pathways underlying white matter involvement in neurodegeneration. With Aβ immunotherapies now entering the clinical realm, gaining a deeper understanding of these processes and the relationships between genotype and phenotype has never been more relevant.

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.

Granule Cells Constitute One of the Major Neuronal Subtypes in the Molecular Layer of the Posterior Cerebellum

The migration of neurons from their birthplace to their correct destination is one of the most crucial steps in brain development. Incomplete or incorrect migration yields ectopic neurons, which cause neurologic deficits or are negligible at best. However, the granule cells (GCs) in the cerebellar cortex may challenge this traditional view of ectopic neurons. When animals are born, GCs proliferate near the pia mater and then migrate down to the GC layer located deep in the cerebellar cortex. However, some GC-like cells stay in the molecular layer, a layer between the pia mater and GC layer, even in normal adult animals. These cells were named ectopic GCs nearly 50 years ago, but their abundance and functional properties remain unclear. Here, we have examined GCs in the molecular layer (mGCs) with a specific marker for mature GCs and transgenic mice in which GCs are sparsely labeled with a fluorescent protein. Contrary to the previous assumption that mGCs are a minor neuronal population, we have found that mGCs are as prevalent as stellate or basket cells in the posterior cerebellum. They are produced during a similar period as regular GCs (rGCs), and in vivo time-lapse imaging has revealed that mGCs are stably present in the molecular layer. Whole-cell patch-clamp recordings have shown that mGCs discharge action potentials similarly to rGCs. Since axonal inputs differ between the molecular layer and GC layer, mGCs might be incorporated in different micro-circuits from rGCs and have a unique functional role in the cerebellum.

Refractory epilepsy in PSEN 1 mutation (I83T)

Mutations in the presenilin-1 gene (PSEN1) on chromosome 14 are the most common cause of autosomal dominant Alzheimer's disease (ADAD), which has a broad clinical phenotype, encompassing not only dementia but a variety of other neurological features. We report the case of a 32 years old man with a family history of  early onset AD associated with a PSEN1 mutation in the exon 4 (I83T). The proband's, carrying the mutation,  present a refractory epilepsy predating cognitive decline. We discuss the physiopathological mechanisms of epilepsy during AD associated with PSEN 1 mutation, the possibility of linking this epilepsy to the mutation?.

Translational Research in Alzheimer's and Prion Diseases

Translational neuroscience integrates the knowledge derived by basic neuroscience with the development of new diagnostic and therapeutic tools that may be applied to clinical practice in neurological diseases. This information can be used to improve clinical trial designs and outcomes that will accelerate drug development, and to discover novel biomarkers which can be efficiently employed to early recognize neurological disorders and provide information regarding the effects of drugs on the underlying disease biology. Alzheimer’s disease (AD) and prion disease are two classes of neurodegenerative disorders characterized by incomplete knowledge of the molecular mechanisms underlying their occurrence and the lack of valid biomarkers and effective treatments. For these reasons, the design of therapies that prevent or delay the onset, slow the progression, or improve the symptoms associated to these disorders is urgently needed. During the last few decades, translational research provided a framework for advancing development of new diagnostic devices and promising disease-modifying therapies for patients with prion encephalopathies and AD. In this review, we provide present evidence of how supportive can be the translational approach to the study of dementias and show some results of our preclinical studies which have been translated to the clinical application following the ‘bed-to-bench-and-back’ research model.

Homozygosity for the A431E mutation in PSEN1 presenting with a relatively aggressive phenotype

OBJECTIVE

We report a 35 year-old male with childhood learning disability and early onset dementia who is homozygous for the A431E variant in the PSEN1 gene. Presenilin1 mutations are associated with autosomal dominant Alzheimer's dementia with young and somewhat stereotyped onset. Such variants may cause Alzheimer's dementia through aberrant processing of amyloid precursor protein through effects on γ-secretase activity. γ-secretase is involved in the cleavage of many proteins critical to normal function, including brain development. Therefore, manifestations in persons without normal Presenilin1 function is of interest.

METHODS

Clinical evaluation including family history, examination, brain MRI, and genetic analysis.

RESULTS

Our patient had mild developmental delay, chronic nighttime behavioral disturbance, and onset of progressive cognitive deficits at age 33. Clinical evaluation demonstrated spastic paraparesis and pseudobulbar affect. Brain MRI revealed cerebral atrophy disproportionate to age. Chronic microhemorrhages within bilateral occipital, temporal, and right frontal lobes were seen. Sanger sequencing confirmed homozygosity for the A431E variant in PSEN1, which is a known pathogenic variant causing autosomal dominant Alzheimer's dementia.

CONCLUSIONS

Our report demonstrates that homozygosity for pathogenic Presenilin1 variants is compatible with life, though may cause a more aggressive phenotype with younger age of onset and possibly REM behavior disorder.

Seizures as an early symptom of autosomal dominant Alzheimer's disease

Our objective was to assess the reported history of seizures in cognitively asymptomatic mutation carriers for autosomal dominant Alzheimer's disease (ADAD) and the predictive value of seizures for mutation carrier status in cognitively asymptomatic first-degree relatives of ADAD patients. Seizure occurrence in the Dominantly Inherited Alzheimer Network observational study was correlated with mutation carrier status in cognitively asymptomatic subjects. Of 276 cognitively asymptomatic individuals, 11 (4%) had experienced seizures, and nine of these carried an ADAD mutation. Thus, in the Dominantly Inherited Alzheimer Network population, seizure frequency in mutation carriers was significantly higher than in noncarriers (p = 0.04), and the positive predictive value of seizures for the presence of a pathogenic mutation was 81.8%. Among cognitively asymptomatic ADAD family members, the occurrence of seizures increases the a priori risk of 50% mutation-positive status to about 80%. This finding suggests that ADAD mutations increase the risk of seizures.

White Matter Abnormalities Track Disease Progression in PSEN1 Autosomal Dominant Alzheimer's Disease

PSEN1 mutations are the most frequent cause of autosomal dominant Alzheimer's disease (ADAD), and show nearly full penetrance. There is presently increasing interest in the study of biomarkers that track disease progression in order to test therapeutic interventions in ADAD. We used white mater (WM) volumetric characteristics and diffusion tensor imaging (DTI) metrics to investigate correlations with the normalized time to expected symptoms onset (relative age ratio) and group differences in a cohort of 36 subjects from PSEN1 ADAD families: 22 mutation carriers, 10 symptomatic (SMC) and 12 asymptomatic (AMC), and 14 non-carriers (NC). Subjects underwent a 3T MRI. WM morphometric data and DTI metrics were analyzed. We found that PSEN1 MC showed significant negative correlation between fractional anisotropy (FA) and the relative age ratio in the genus and body of corpus callosum and corona radiate (p <  0.05 Family-wise error correction (FWE) at cluster level) and positive correlation with mean diffusivity (MD), axial diffusivity (AxD), and radial diffusivity (RD) in the splenium of corpus callosum. SMC presented WM volume loss, reduced FA and increased MD, AxD, and RD in the anterior and posterior corona radiate, corpus callosum (p <  0.05 FWE) compared with NC. No significant differences were observed between AMC and NC in WM volume or DTI measures. These findings suggest that the integrity of the WM deteriorates linearly in PSEN1 ADAD from the early phases of the disease; thus DTI metrics might be useful to monitor the disease progression. However, the lack of significant alterations at the preclinical stages suggests that these indexes might not be good candidates for early markers of the disease.

White matter hyperintensities are a core feature of Alzheimer's disease: Evidence from the dominantly inherited Alzheimer network

OBJECTIVE

White matter hyperintensities (WMHs) are areas of increased signal on T2-weighted magnetic resonance imaging (MRI) scans that most commonly reflect small vessel cerebrovascular disease. Increased WMH volume is associated with risk and progression of Alzheimer's disease (AD). These observations are typically interpreted as evidence that vascular abnormalities play an additive, independent role contributing to symptom presentation, but not core features of AD. We examined the severity and distribution of WMH in presymptomatic PSEN1, PSEN2, and APP mutation carriers to determine the extent to which WMH manifest in individuals genetically determined to develop AD.

METHODS

The study comprised participants (n = 299; age = 39.03 ± 10.13) from the Dominantly Inherited Alzheimer Network, including 184 (61.5%) with a mutation that results in AD and 115 (38.5%) first-degree relatives who were noncarrier controls. We calculated the estimated years from expected symptom onset (EYO) by subtracting the affected parent's symptom onset age from the participant's age. Baseline MRI data were analyzed for total and regional WMH. Mixed-effects piece-wise linear regression was used to examine WMH differences between carriers and noncarriers with respect to EYO.

RESULTS

Mutation carriers had greater total WMH volumes, which appeared to increase approximately 6 years before expected symptom onset. Effects were most prominent for the parietal and occipital lobe, which showed divergent effects as early as 22 years before estimated onset.

INTERPRETATION

Autosomal-dominant AD is associated with increased WMH well before expected symptom onset. The findings suggest the possibility that WMHs are a core feature of AD, a potential therapeutic target, and a factor that should be integrated into pathogenic models of the disease. Ann Neurol 2016;79:929-939.

Genetic heterogeneity in Alzheimer disease and implications for treatment strategies

Since the original publication describing the illness in 1907, the genetic understanding of Alzheimer's disease (AD) has advanced such that it is now clear that it is a genetically heterogeneous condition, the subtypes of which may not uniformly respond to a given intervention. It is therefore critical to characterize the clinical and preclinical stages of AD subtypes, including the rare autosomal dominant forms caused by known mutations in the PSEN1, APP, and PSEN2 genes that are being studied in the Dominantly Inherited Alzheimer Network study and its associated secondary prevention trial. Similar efforts are occurring in an extended Colombian family with a PSEN1 mutation, in APOE ε4 homozygotes, and in Down syndrome. Despite commonalities in the mechanisms producing the AD phenotype, there are also differences that reflect specific genetic origins. Treatment modalities should be chosen and trials designed with these differences in mind. Ideally, the varying pathological cascades involved in the different subtypes of AD should be defined so that both areas of overlap and of distinct differences can be taken into account. At the very least, clinical trials should determine the influence of known genetic factors in post hoc analyses.

Seizures and dementia in the elderly: Nationwide Inpatient Sample 1999-2008

OBJECTIVES

This study aimed to examine the association between incidence of admission for a primary diagnosis of "seizure" or "epilepsy" and dementia in a nationally representative database, the Nationwide Inpatient Sample, among the elderly population (55 years of age and above) and to determine whether this relationship is different in individuals with Alzheimer's dementia versus those with non-Alzheimer's dementia.

METHODS

Data were obtained from the Nationwide Inpatient Sample using appropriate ICD-9 codes. Frequencies and descriptive analysis adjusting for influence of comorbidities and confounders were utilized. A multivariate logistic regression model adjusted for age, gender, and race was used to further explore the relationship.

RESULTS

Those with AD had a higher risk of developing seizures or epilepsy (OR=3.07, 95% CI=2.98-3.16) as compared with cases with NAD (OR=2.20, 95% CI=2.14-2.27). After adjusting for age, the association increased for patients with AD (OR=4.065, 95% CI=3.95-4.17) but not appreciably for patients with NAD (OR=2.68, 95% CI=2.60-2.75). Adding gender and race to the model did not change the relationship for either AD or NAD. Further adjustment for African-American race did not further change the relationship for AD and seizure (OR=3.96, 95% CI=3.854-4.077) as well as for NAD and seizure (OR=2.652, 95% CI=2.575-2.731). Similarly, Hispanic race did not change the relationship significantly for AD (OR=4.1, 95% CI=4.01-4.25) and NAD (OR=2.65, 95% CI=2.56-2.74).

CONCLUSION

Patients with AD have a higher prevalence of a seizure compared with patients with NAD. Younger patients with AD were more likely to have seizures. Race, when analyzed as a whole and separately as African-American and Hispanic race, did not alter this relationship.

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.

Antisense reduction of tau in adult mice protects against seizures

Tau, a microtubule-associated protein, is implicated in the pathogenesis of Alzheimer's Disease (AD) in regard to both neurofibrillary tangle formation and neuronal network hyperexcitability. The genetic ablation of tau substantially reduces hyperexcitability in AD mouse lines, induced seizure models, and genetic in vivo models of epilepsy. These data demonstrate that tau is an important regulator of network excitability. However, developmental compensation in the genetic tau knock-out line may account for the protective effect against seizures. To test the efficacy of a tau reducing therapy for disorders with a detrimental hyperexcitability profile in adult animals, we identified antisense oligonucleotides that selectively decrease endogenous tau expression throughout the entire mouse CNS--brain and spinal cord tissue, interstitial fluid, and CSF--while having no effect on baseline motor or cognitive behavior. In two chemically induced seizure models, mice with reduced tau protein had less severe seizures than control mice. Total tau protein levels and seizure severity were highly correlated, such that those mice with the most severe seizures also had the highest levels of tau. Our results demonstrate that endogenous tau is integral for regulating neuronal hyperexcitability in adult animals and suggest that an antisense oligonucleotide reduction of tau could benefit those with epilepsy and perhaps other disorders associated with tau-mediated neuronal hyperexcitability.

APP mutations in the Aβ coding region are associated with abundant cerebral deposition of Aβ38

Aβ is the main component of amyloid deposits in Alzheimer disease (AD) and its aggregation into oligomers, protofibrils and fibrils is considered a seminal event in the pathogenesis of AD. Aβ with C-terminus at residue 42 is the most abundant species in parenchymal deposits, whereas Aβ with C-terminus at residue 40 predominates in the amyloid of the walls of large vessels. Aβ peptides with other C-termini have not yet been thoroughly investigated. We analysed Aβ38 in the brains of patients with Aβ deposition linked to sporadic and familial AD, hereditary cerebral haemorrhage with amyloidosis, or Down syndrome. Immunohistochemistry, confocal microscopy, immunoelectron microscopy, immunoprecipitation and the electrophoresis separation of low molecular weight aggregates revealed that Aβ38 accumulates consistently in the brains of patients carrying APP mutations in the Aβ coding region, but was not detected in the patients with APP mutations outside the Aβ domain, in the patients with presenilin mutations or in subjects with Down syndrome. In the patients with sporadic AD, Aβ38 was absent in the senile plaques, but it was detected only in the vessel walls of a small subset of patients with severe cerebral amyloid angiopathy. Our results suggest that APP mutations in the Aβ coding region favour Aβ38 accumulation in the brain and that the molecular mechanisms of Aβ deposition in these patients may be different from those active in patients with familial AD associated with other genetic defects and sporadic AD.

Cerebrospinal fluid biomarkers and proximity to diagnosis in preclinical familial Alzheimer's disease

BACKGROUND/AIMS

Biological markers of utility in tracking Alzheimer's disease (AD) during the presymptomatic prodromal phase are important for prevention studies. Changes in cerebrospinal fluid (CSF) levels of 42-amino-acid β-amyloid (Aβ(42)), total tau protein (t-tau) and phosphorylated tau at residue 181 (p-tau(181)) during this state are incompletely characterized.

METHODS

We measured CSF markers in 13 carriers of familial AD (FAD) mutations that are fully penetrant for causing AD (PSEN1 and APP) and in 5 non-mutation-carrying family members.

RESULTS

Even among the entirely presymptomatic mutation carriers (n = 9), Aβ(42) was diminished (388.7 vs. 618.4 pg/ml, p = 0.004), and t-tau (138.5 vs. 50.5 pg/ml, p = 0.002) and p-tau(181) (71.7 vs. 24.6 pg/ml, p = 0.003) were elevated. There was a negative correlation between Aβ(42) levels and age relative to the family-specific age of dementia diagnosis.

CONCLUSIONS

Our data are consistent with a decline in CSF Aβ(42) levels occurring at least 20 years prior to clinical dementia in FAD.

Presenilin-1 mutation Alzheimer's disease: a genetic epilepsy syndrome?

Mutations in the presenilin-1 gene (PSEN1) on chromosome 14 are the most common cause of autosomal dominant Alzheimer's disease (AD), with around 180 mutations described to date. PSEN1 AD has a broad clinical phenotype, encompassing not only dementia but a variety of other neurological features which may include epileptic seizures. Around 20% of recorded PSEN1 mutations have been reported to be associated with epileptic seizures, sometimes occurring as an early feature of disease, sometimes late. The epilepsy-associated PSEN1 mutations are spread throughout the PSEN1 gene. This frequency of seizure-associated PSEN1 mutations may be an underestimate, as epileptic seizures may not be recognized as such in the context of a dementing disorder, perhaps being labeled as "confusion" or delirious episodes. A high index of clinical suspicion for epileptic seizures in PSEN1 AD is therefore appropriate. The neuropathological substrates of PSEN1 AD-related seizures remain to be determined, as few such cases have undergone detailed neuropathological examination. Nevertheless, PSEN1 AD should now be recognized, using the new International League Against Epilepsy nomenclature, as a genetic epilepsy syndrome.

A perfect storm: Converging paths of epilepsy and Alzheimer's dementia intersect in the hippocampal formation

Seizures in the human temporal lobe transiently impair cognition and steadily damage hippocampal circuitry, leading to progressive memory loss. Similarly, the toxic accumulation of Aβ peptides underlying Alzheimer's disease (AD) triggers synaptic degeneration, circuit remodeling, and abnormal synchronization within the same networks. Because neuronal hyperexcitability amplifies the synaptic release of Aβ, seizures create a vicious spiral that accelerates cell death and cognitive decline in the AD brain. The confluence of hyperexcitability and excitotoxicity, combined with the challenge of seizure detection in the human hippocampus, make epilepsy in these individuals extremely important to correctly diagnose and treat. Emerging clinical evidence reveals an elevated comorbidity of epilepsy in AD, particularly when linked to mutations in the APP/Aβ gene pathway. Experimental models in genetically engineered mice confirm and extend these findings, highlighting the presence of subclinical seizures and overlapping pathophysiologic cascades. There is an urgent need for more clinical and basic investigation to improve the early recognition of hippocampal seizures arising during the course of dementing disorders, and to validate molecular blockers of Aβ-induced aberrant excitability that can slow and potentially reverse the progression of cognitive decline.

Neuropathology of the recessive A673V APP mutation: Alzheimer disease with distinctive features

Mutations of three different genes, encoding β-amyloid precursor protein (APP), presenilin 1 and presenilin 2 are associated with familial Alzheimer's disease (AD). Recently, the APP mutation A673V has been identified that stands out from all the genetic defects previously reported in these three genes, since it causes the disease only in the homozygous state (Di Fede et al. in Science 323:1473-1477, 2009). We here provide the detailed neuropathological picture of the proband of this family, who was homozygous for the APP A673V mutation and recently came to death. The brain has been studied by histological and immunohistochemical techniques, at the optical and ultrastructural levels. Cerebral Aβ accumulation and tau pathology were severe and extensive. Peculiar features were the configuration of the Aβ deposits that were of large size, mostly perivascular and exhibited a close correspondence between the pattern elicited by amyloid stainings and the labeling obtained with immunoreagents specific for Aβ40 or Aβ42. Moreover, Aβ deposition spared the neostriatum while deeply affecting the cerebellum, and therefore was not in compliance with the hierarchical topographical sequence of involvement documented in sporadic AD. Therefore, the neuropathological picture of familial AD caused by the APP recessive mutation A673V presents distinctive characteristics compared to sporadic AD or familial AD inherited as a dominant trait. Main peculiar features are the morphology, structural properties and composition of the Aβ deposits as well as their topographic distribution in the brain.

Alzheimer's secretases regulate voltage-gated sodium channels

BACE1 and presenilin (PS)/γ-secretase are primary proteolytic enzymes responsible for the generation of pathogenic amyloid β-peptides (Aβ) in Alzheimer's disease. We and others have found that β-subunits of the voltage-gated sodium channel (Na(v)βs) also undergo sequential proteolytic cleavages mediated by BACE1 and PS/γ-secretase. In a follow-up study, we reported that elevated BACE1 activity regulates total and surface expression of voltage-gated sodium channels (Na(v)1 channels) and thereby modulates sodium currents in neuronal cells and mouse brains. In this review, we focus on the molecular mechanism of how BACE1 and PS/γ-secretase regulate Na(v)1 channels in neuronal cells. We will also discuss potential physiological and pathological roles of BACE1- and PS/γ-secretase-mediated processing of Na(v)βs in relation to Na(v)1 channel function.

Mutant presenilin 1 increases the expression and activity of BACE1

Mutations of the presenilin 1 (PS1) gene are the most common cause of early onset familial Alzheimer disease (FAD). PS1 mutations alter the activity of the gamma-secretase on the beta-amyloid precursor protein (APP), leading to selective overproduction of beta-amyloid (Abeta) 42 peptides, the species that forms oligomers that may exert toxic effects on neurons. Here we show that PS1 mutations, expressed both transiently and stably, in non-neuronal and neuronal cell lines increase the expression and the activity of the beta-secretase (BACE1), the rate-limiting step of Abeta production. Also, BACE1 expression and activity are elevated in brains of PS1 mutant knock-in mice compared with wild type littermates as well as in cerebral cortex of FAD cases bearing various PS1 mutations compared with in sporadic AD cases and controls. The up-regulation of BACE1 by PS1 mutations requires the gamma-secretase cleavage of APP and is proportional to the amount of secreted Abeta42. Abeta42, and not AICD (APP intracellular domain), is indeed the APP derivative that mediates the overexpression of BACE1. The effect of PS1 mutations on BACE1 may contribute to determine the wide clinical and pathological phenotype of early onset FAD.

Epilepsy and dementia in the elderly

Epilepsy is a frequent condition in the elderly; however, it remains a relatively understudied condition in older adults with dementia. The diagnosis of a seizure is particularly difficult and is most often based on questions to the caregiver. Epilepsy in dementia has significant consequences on the prognosis of the underlying dementia: it can result in a worsening of cognitive performance, particularly in language, as well as a reduction in autonomy, a greater risk of injury and a higher mortality rate. In this review, management strategies are recommended for the clinician. The presence of pre-existing Alzheimer's disease does not exempt the clinician from ruling out other symptomatic causes of seizures. Anti-epileptic drugs (AED) should be started only after the diagnosis has been clearly established, when the risk of recurrence is high, and with monotherapy whenever possible. Although few data are available, the more recent AED offer significant advantages over the older medications in this context.

Presenilin-1 280Glu-->Ala mutation alters C-terminal APP processing yielding longer abeta peptides: implications for Alzheimer's disease

Presenilin (PS) mutations enhance the production of the Abeta42 peptide that is derived from the amyloid precursor protein (APP). The pathway(s) by which the Abeta42 species is preferentially produced has not been elucidated, nor is the mechanism by which PS mutations produce early-onset dementia established. Using a combination of histological, immunohistochemical, biochemical, and mass spectrometric methods, we examined the structural and morphological nature of the amyloid species produced in a patient expressing the PS1 280Glu-->Ala familial Alzheimer's disease mutation. Abundant diffuse plaques were observed that exhibited a staining pattern and morphology distinct from previously described PS cases, as well as discreet amyloid plaques within the white matter. In addition to finding increased amounts of CT99 and Abeta42 peptides, our investigation revealed the presence of a complex array of Abeta peptides substantially longer than 42/43 amino acid residue species. The increased hydrophobic nature of longer Abeta species retained within the membrane walls could impact the structure and function of plasma membrane and organelles. These C-terminally longer peptides may, through steric effects, dampen the rate of turnover by critical amyloid degrading enzymes such as neprilysin and insulin degrading enzyme. A complete understanding of the deleterious side effects of membrane bound Abeta as a consequence of gamma-secretase alterations is needed to understand Alzheimer's disease pathophysiology and will aid in the design of therapeutic interventions.

Does epileptiform activity contribute to cognitive impairment in Alzheimer's disease?

Alzheimer's disease is a devastating neurological disorder. The role of hyperexcitability in the disease's cognitive decline is not completely understood. In this issue of Neuron, Palop et al. report both limbic seizures and presumed homeostatic responses to seizures in an animal model of Alzheimer's.

Early-onset Alzheimer's disease with a de novo mutation in the presenilin 1 gene

A 32-year-old woman diagnosed with very rapidly progressing early-onset Alzheimer's disease (EOAD), age of onset 29 years, and S170F mutation in presenilin 1 gene (PSEN1) is presented. Neuroimaging conducted 2 years after the first symptoms was typical for the advanced stage of Alzheimer's disease (AD), showing cortical brain atrophy, particularly within hippocampus, frontal and temporal cortex. The unaffected parents of the proband are not carriers of the mutation. The paternity was confirmed by microsatellite typing, strongly suggesting de novo origin of S170F mutation. In silico modeling of S170F mutation impact on presenilin 1 (PS1) transmembrane structure indicates that the mutation considerably alters putative interactions of PS1 with other proteins within gamma-secretase complex.

The Genetics of Very Early Onset Alzheimer Disease

OBJECTIVE

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

CA1 hippocampal neuronal loss in familial Alzheimer's disease presenilin-1 E280A mutation is related to epilepsy

PURPOSE

Alzheimer disease (AD) and epilepsy are brain disorders frequently associated with neuronal cell loss in mesial temporal lobe structures, but presenting different patterns of damage. Recently it was proposed that a causal relation may exist between AD pathology and the appearance of epilepsy in some cases with AD. This study aimed to determine the neuronal loss in CA1 hippocampal region from patients bearing the presenilin-1 [E280A] mutation (PS1[E280A]) associated with seizures.

METHODS

Coronal sections from the hippocampal formation (anterior one third) from controls (n = 5) and familial AD (FAD; n = 8) patients were stained by using thionin and thioflavine-S staining to evaluate the number of neurons in the CA1 field, beta-plaques, and neurofibrillary tangles, respectively.

RESULTS

Two distinct patterns of neuronal loss in the CA1 field of FAD patients were found: (a) diffuse-patchy neuronal loss (three FAD nonepilepsy patients) characterized by both a general decrease of neurons and the presence of multiple, small regions devoid of neurons; and (b) sclerotic-like neuronal loss (five FAD epilepsy patients) similar to that found typically in the CA1 field of epilepsy patients with hippocampal sclerosis.

CONCLUSIONS

This investigation shows for the first time CA1 neuronal depopulation in a subpopulation of patients (five of eight) bearing the PS1[E280A] mutation with epileptic seizures, indicating a relation between hippocampal neuronal loss and epileptic seizures in FAD patients.

Neuropathological and clinical phenotype of an Italian Alzheimer family with M239V mutation of presenilin 2 gene

Presenilin 1 and 2 are 2 highly homologous genes involved in familial Alzheimer disease. While more than 100 mutations in presenilin 1 are known to segregate with the disease in familial Alzheimer disease, only 9 mutations of presenilin 2 have been identified to date. We report the clinical and neuropathological phenotype of FLO10, the large Italian Alzheimer kindred associated with methionine to valine substitution at residue 239 of presenilin 2. The patients showed a remarkable variability in age of onset of symptoms, disease duration, and clinical presentation. The neuropathological study of 2 patients revealed peculiar features in addition to neurofibrillary changes and A beta amyloid deposits in the neuropil and vessel wall. Ectopic neurons in the subcortical white matter, often containing neurofibrillary tangles, were found in both patients, one of whom presented with epilepsy. Furthermore, 1 patient showed an unusually high number of ghost tangles in the cerebral cortex. These observations indicate that the Alzheimer kindred FLO10 associated with M239V mutation of presenilin 2 is characterized by some peculiarities of the clinical and neuropathologic phenotype compared to sporadic Alzheimer disease.