Familial Alzheimer's disease. A pedigree with a mis-sense mutation in the amyloid precursor protein gene (amyloid precursor protein 717 valine-->glycine)

Neuronal Network Excitability in Alzheimer's Disease: The Puzzle of Similar versus Divergent Roles of Amyloid β and Tau

Alzheimer’s disease (AD) is the most frequent neurodegenerative disorder that commonly causes dementia in the elderly. Recent evidence indicates that network abnormalities, including hypersynchrony, altered oscillatory rhythmic activity, interneuron dysfunction, and synaptic depression, may be key mediators of cognitive decline in AD. In this review, we discuss characteristics of neuronal network excitability in AD, and the role of Aβ and tau in the induction of network hyperexcitability. Many patients harboring genetic mutations that lead to increased Aβ production suffer from seizures and epilepsy before the development of plaques. Similarly, pathologic accumulation of hyperphosphorylated tau has been associated with hyperexcitability in the hippocampus. We present common and divergent roles of tau and Aβ on neuronal hyperexcitability in AD, and hypotheses that could serve as a template for future experiments.

Gene mutations associated with early onset familial Alzheimer's disease in China: An overview and current status

BACKGROUND

Mutations of three causative genes, namely presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP), have been identified as the major causes of early-onset familial Alzheimer's disease (EOFAD). The prevalence of causative gene mutations in patients with EOFAD has been reported in previous studies worldwide but remains unclear in China. The patients with these known mutations always show considerable clinical phenotypic variability. However, to date, there have been no detailed descriptions of the clinical phenotypes associated with these Chinese EOFAD mutations. Thus, the aim of this study was to describe all of the known mutations in three EOFAD causative genes and genotype-phenotype correlations in Chinese patients with EOFAD.

METHOD

We systematically searched the PubMed, MEDLINE, CNKI, VIP, and WAN-FANG databases to find Chinese EOFAD mutations in reports from inception through May 2020.

RESULT

We identified 31 studies reporting mutations of three causative genes in China. 10 mutations in APP gene, 27 mutations in PSEN1 gene and six mutations in PSEN2 were discovered in Chinese EOFAD. This review summarized all these probably pathogenic mutations as well as its clinical features. To the best of our knowledge, this is the first systemic review of causative gene mutations in patients with EOFAD in China.

CONCLUSION

The analysis of the genetic and clinical phenotype correlations in this review supports the idea that the clinical phenotype might be influenced by specific genetic defects. It also suggests genetic testing and genotype-phenotype correlations are important for the accurate diagnosis and for understanding disease-associated pathways and might also improve disease therapy and prevention.

Impairment of memory generalization in preclinical autosomal dominant Alzheimer's disease mutation carriers

Fast, inexpensive, and noninvasive identification of Alzheimer's disease (AD) before clinical symptoms emerge would augment our ability to intervene early in the disease. Individuals with fully penetrant genetic mutations causing autosomal dominant Alzheimer's disease (ADAD) are essentially certain to develop the disease, providing a unique opportunity to examine biomarkers during the preclinical stage. Using a generalization task that has previously shown to be sensitive to medial temporal lobe pathology, we compared preclinical individuals carrying ADAD mutations to noncarrying kin to determine whether generalization (the ability to transfer previous learning to novel but familiar recombinations) is vulnerable early, before overt cognitive decline. As predicted, results revealed that preclinical ADAD mutation carriers made significantly more errors during generalization than noncarrying kin, despite no differences between groups during learning or retention. This impairment correlated with the left hippocampal volume, particularly in mutation carriers. Such identification of generalization deficits in early ADAD may provide an easily implementable and potentially linguistically and culturally neutral way to identify and track cognition in ADAD.

Network abnormalities and interneuron dysfunction in Alzheimer disease

The function of neural circuits and networks can be controlled, in part, by modulating the synchrony of their components' activities. Network hypersynchrony and altered oscillatory rhythmic activity may contribute to cognitive abnormalities in Alzheimer disease (AD). In this condition, network activities that support cognition are altered decades before clinical disease onset, and these alterations predict future pathology and brain atrophy. Although the precise causes and pathophysiological consequences of these network alterations remain to be defined, interneuron dysfunction and network abnormalities have emerged as potential mechanisms of cognitive dysfunction in AD and related disorders. Here, we explore the concept that modulating these mechanisms may help to improve brain function in these conditions.

Clinical characterization of an APP mutation (V717I) in five Han Chinese families with early-onset Alzheimer's disease

The missense mutation V717I in amyloid precursor protein (APP) gene has been reported in many early-onset familial Alzheimer's disease (EOFAD) families. However, no detailed clinical picture regarding this mutation has ever been described for Chinese EOFAD. We investigate the age at onset (AAO), initial clinical features and non-cognitive neurological symptoms in 34 affected subjects from five Han Chinese EOFAD families with the APPV717I mutation to characterize the clinical phenotype. The AAO was 54.7±4.9years (n=34), with the APOE ɛ4 allele correlating with a decreased AAO. Prominent early affective symptoms, executive dysfunction and disorientation at onset were exhibited in 26 (76.5%), 18 (52.9%) and 16 (47%) cases, respectively. Spastic paraparesis and cerebellar ataxia occurred frequently in 13 (38.2%) and 12 (35.3%) cases, respectively, during the late stages of disease. The specific clinical phenotype of the APPV717I mutation for Chinese families is characterized by prominent early affective symptoms, executive dysfunction and disorientation as well as frequent late spastic paraparesis and cerebellar ataxia as compared to Western reports. We conclude that ethnic differences, environment or additional unknown factors may challenge the homogeneity of EOFAD with identical APP mutations.

Clinical phenotype and genetic associations in autosomal dominant familial Alzheimer's disease: a case series

BACKGROUND

The causes of phenotypic heterogeneity in familial Alzheimer's disease with autosomal dominant inheritance are not well understood. We aimed to characterise clinical phenotypes and genetic associations with APP and PSEN1 mutations in symptomatic autosomal dominant familial Alzheimer's disease (ADAD).

METHODS

We retrospectively analysed genotypic and phenotypic data (age at symptom onset, initial cognitive or behavioural symptoms, and presence of myoclonus, seizures, pyramidal signs, extrapyramidal signs, and cerebellar signs) from all individuals with ADAD due to APP or PSEN1 mutations seen at the Dementia Research Centre in London, UK. We examined the frequency of presenting symptoms and additional neurological features, investigated associations with age at symptom onset, APOE genotype, and mutation position, and explored phenotypic differences between APP and PSEN1 mutation carriers. The proportion of individuals presenting with various symptoms was analysed with descriptive statistics, stratified by mutation type.

FINDINGS

Between July 1, 1987, and Oct 31, 2015, age at onset was recorded for 213 patients (168 with PSEN1 mutations and 45 with APP mutations), with detailed history and neurological examination findings available for 121 (85 with PSEN1 mutations and 36 with APP mutations). We identified 38 different PSEN1 mutations (four novel) and six APP mutations (one novel). Age at onset differed by mutation, with a younger onset for individuals with PSEN1 mutations than for those with APP mutations (mean age 43·6 years [SD 7·2] vs 50·4 years [SD 5·2], respectively, p<0·0001); within the PSEN1 group, 72% of age at onset variance was explained by the specific mutation. A cluster of five mutations with particularly early onset (mean age at onset <40 years) involving PSEN1's first hydrophilic loop suggests critical functional importance of this region. 71 (84%) individuals with PSEN1 mutations and 35 (97%) with APP mutations presented with amnestic symptoms, making atypical cognitive presentations significantly more common in PSEN1 mutation carriers (n=14; p=0·037). Myoclonus and seizures were the most common additional neurological features; individuals with myoclonus (40 [47%] with PSEN1 mutations and 12 [33%] with APP mutations) were significantly more likely to develop seizures (p=0·001 for PSEN1; p=0·036 for APP), which affected around a quarter of the patients in each group (20 [24%] and nine [25%], respectively). A number of patients with PSEN1 mutations had pyramidal (21 [25%]), extrapyramidal (12 [14%]), or cerebellar (three [4%]) signs.

INTERPRETATION

ADAD phenotypes are heterogeneous, with both age at onset and clinical features being influenced by mutation position as well as causative gene. This highlights the importance of considering genetic testing in young patients with dementia and additional neurological features in order to appropriately diagnose and treat their symptoms, and of examining different mutation types separately in future research.

FUNDING

Medical Research Council and National Institute for Health Research.

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

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

Posttraumatic stress disorder-like induction elevates β-amyloid levels, which directly activates corticotropin-releasing factor neurons to exacerbate stress responses

Recent studies have found that those who suffer from posttraumatic stress disorder (PTSD) are more likely to experience dementia as they age, most often Alzheimer's disease (AD). These findings suggest that the symptoms of PTSD might have an exacerbating effect on AD progression. AD and PTSD might also share common susceptibility factors such that those who experience trauma-induced disease were already more likely to succumb to dementia with age. Here, we explored these two hypotheses using a mouse model of PTSD in wild-type and AD model animals. We found that expression of human familial AD mutations in amyloid precursor protein and presenilin 1 leads to sensitivity to trauma-induced PTSD-like changes in behavioral and endocrine stress responses. PTSD-like induction, in turn, chronically elevates levels of CSF β-amyloid (Aβ), exacerbating ongoing AD pathogenesis. We show that PTSD-like induction and Aβ elevation are dependent on corticotropin-releasing factor (CRF) receptor 1 signaling and an intact hypothalamic-pituitary-adrenal axis. Furthermore, we show that Aβ species can hyperexcite CRF neurons, providing a mechanism by which Aβ influences stress-related symptoms and PTSD-like phenotypes. Consistent with Aβ causing excitability of the stress circuitry, we attenuate PTSD-like phenotypes in vivo by lowering Aβ levels during PTSD-like trauma exposure. Together, these data demonstrate that exposure to PTSD-like trauma can drive AD pathogenesis, which directly perturbs CRF signaling, thereby enhancing chronic PTSD symptoms while increasing risk for AD-related dementia.

Seizures in Alzheimer's disease

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

Early-onset familial Alzheimer's disease (EOFAD)

Early-onset familial Alzheimer's disease (EOFAD) is a condition characterized by early onset dementia (age at onset < 65 years) and a positive family history for dementia. To date, 230 mutations in presenilin (PS1, PS2) and amyloid precursor protein (APP) genes have been identified in EOFAD. The mutations within these three genes (PS1/PS2/APP) affect a common pathogenic pathway in APP synthesis and proteolysis, which lead to excessive production of amyloid β. Compared with sporadic Alzheimer's disease (AD), EOFAD has some distinctive features including early age at onset, positive familial history, a variety of non-cognitive neurological symptoms and signs, and a more aggressive course. There is marked phenotypic heterogeneity among different mutations of EOFAD. Studies in presymptomatic mutation carriers reveal biomarkers abnormalities. EOFAD diagnosis is based on clinical and family history, neurological symptoms and examination, biomarker features, as well as genotyping in some cases. New therapeutic agents targeting amyloid formation may benefit EOFAD individuals.

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.

Beta-secretase: structure, function, and evolution

The most popular current hypothesis is that Alzheimer's disease (AD) is caused by aggregates of the amyloid peptide (Abeta), which is generated by cleavage of the Abeta protein precursor (APP) by beta-secretase (BACE-1) followed by gamma-secretase. BACE-1 cleavage is limiting for the production of Abeta, making it a particularly good drug target for the generation of inhibitors that lower Abeta. A landmark discovery in AD was the identification of BACE-1 (a.k.a. Memapsin-2) as a novel class of type I transmembrane aspartic protease. Although BACE-2, a homologue of BACE-1, was quickly identified, follow up studies using knockout mice demonstrated that BACE-1 was necessary and sufficient for most neuronal Abeta generation. Despite the importance of BACE-1 as a drug target, development has been slow due to the incomplete understanding of its function and regulation and the difficulties in developing a brain penetrant drug that can specifically block its large catalytic pocket. This review summarizes the biological properties of BACE-1 and attempts to use phylogenetic perspectives to understand its function. The article also addresses the challenges in discovering a selective drug-like molecule targeting novel mechanisms of BACE-1 regulation.

Neuropsychological function in nondemented carriers of presenilin-1 mutations

BACKGROUND

Prospective and case-control studies have demonstrated that memory loss and executive dysfunction occur early in Alzheimer disease (AD).

OBJECTIVE

To investigate these observations by the study of persons at risk for autosomal dominant forms of AD.

METHODS

Neuropsychological and genetic tests were performed on 51 nondemented at-risk members of 10 Mexican families with two distinct presenilin-1 (PS1) mutations. Test scores were compared between PS1 mutation carriers (MCs; n = 30) and noncarriers (NCs; n = 21) by analyses of variance, co-varying for family and specific mutation. Regression analyses were performed, taking into account age relative to the median age at dementia diagnosis in the family (adjusted age), gender, Beck Depression Inventory (BDI) scores, education, and number of APOE epsilon4 alleles. Subjects were divided into age tertiles and scores compared within these groups. Composite scores for Verbal Memory, Executive Function/Working Memory, Language, and Visuospatial Function were created, and these scores compared between MCs and NCs.

RESULTS

MCs performed worse than NCs on the Mini-Mental State Examination, Trails Making Tests A and B, Delayed Recall of a 10-Word List, and Wechsler Adult Intelligence Scale WAIS Block Design. In multiple linear regression analyses, BDI score, gender, and number of APOE epsilon4 alleles did not consistently affect test scores. The differences seen between MCs and NCs were due to differences in the oldest tertile. MCs had lower Visuospatial and Executive Function/Working Memory but not Verbal Memory or Language composite scores.

CONCLUSIONS

This study is consistent with findings in sporadic Alzheimer disease of early problems with memory, visuospatial function, and particularly with executive function in PS1 mutation carriers. Depression, gender, and presence of an APOE epsilon4 allele did not demonstrate large influences on neuropsychological performance.

What the study of persons at risk for familial Alzheimer's disease can tell us about the earliest stages of the disorder: a review

As the proportion of elderly persons continues to expand, understanding the pathobiology of Alzheimer's disease and being able to diagnose it at an early stage become more critical. A minority of Alzheimer's disease cases are inherited as a fully-penetrant, autosomal dominant trait with a young age of onset. The molecular study of the pathogenic mutations has led to insights regarding the etiology of sporadic Alzheimer's disease. Clinical studies in persons at risk for these mutations have confirmed early episodic memory and executive deficits in Alzheimer's disease and suggested that dysphoria may precede the cognitive changes of Alzheimer's disease. Imaging studies have indicated that medial temporal lobe atrophy begins 3 to 4 years before cognitive symptoms, and quantitative cerebral metabolic changes are also present from early on. Studies of biochemical markers suggest that elevations of plasma A 1-42 occur early in familial Alzheimer's disease but that tau may not be elevated in cerebrospinal fluid until the disease is more advanced.

Cerebellar diffuse amyloid plaques are derived from dendritic Abeta42 accumulations in Purkinje cells

beta-amyloid(1-42) (Abeta42)-rich amyloid plaques (APs) may be derived from destroyed neurons that were burdened with extensive intracellular Abeta42 accumulations. Since most cells that accumulate Abeta42 express the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), we examined the relationship between the intracellular accumulation of Abeta42 and the expression of the alpha7nAChR in cells from the cerebellum of sporadic Alzheimer's disease (AD) patients. Abeta42, but not Abeta40 or Abeta43, accumulates intracellularly in Purkinje, Golgi II, stellate and basket cells in the AD cerebellum, all of which express the alpha7nAChR. Abeta42 deposits were also prominent within dendrites of Purkinje cells, especially at points of their bifurcation that were often occluded with this material. Diffuse APs appeared to represent the remnants of destroyed Abeta42-laden segments of Purkinje cell dendritic trees. Similarly, the accumulation of Abeta42 and early loss of Golgi II cells in AD cerebella correlated directly to their high level of alpha7nAChR expression. Furthermore, the presence and relative abundance of neuron-derived Abeta42/alpha7nAChR-positive materials within Bergman glia may be indicative of the stage of AD. These data are consistent with a role for the alpha7nAChR in mediating intracellular Abeta42 accumulation and also support the notion that the intracellular and intradendritic accumulation of Abeta42 may eventually result in cell lysis and the formation of APs.

Distinguishable effects of presenilin-1 and APP717 mutations on amyloid plaque deposition

Both APP and PS-1 are causal genes for early-onset familial Alzheimer's disease (AD) and their mutation effects on cerebral Abeta deposition in the senile plaques were examined in human brains of 29 familial AD (23 PS-1, 6 APP) cases and 14 sporadic AD cases in terms of Abeta40 and Abeta42. Abeta isoform data were evaluated using repeated measures analysis of variance which adjusted for within-subject measurement variation and confounding effects of individual APP and PS-1 mutations, age at onset, duration of illness and APOE genotype. We observed that mutations in both APP and PS-1 were associated with a significant increase of Abeta42 in plaques as been documented previously. In comparison to sporadic AD cases, both APP717 and PS-1 mutation cases had an increased density (measured as the number of plaques/mm(2)) and area (%) of Abeta42 plaques. However, we found an unexpected differential effect of PS-1 but not APP717 mutation cases. At least some of PS-1 but not APP717 mutation cases had the significant increase of density and area of Abeta40-plaques as compared to sporadic AD independently of APOE genotype. Our results suggest that PS-1 mutations affect cerebral accumulation of Abeta burden in a different fashion from APP717 mutations in their familial AD brains.

Alzheimer's disease due to an intronic presenilin-1 (PSEN1 intron 4) mutation: A clinicopathological study

We describe 21 affected individuals from a kindred with early-onset autosomal dominant familial Alzheimer's disease caused by an intronic presenilin-1 mutation (in intron 4). Mean age at onset of symptoms was 37.4 years [95% confidence interval (CI): 36.6-38.2 years], mean age at death was 44.7 years (95% CI: 43.1-46.3 years) and mean duration of illness was 7.3 years (95% CI: 5.9-8.7 years). Myoclonus and seizures were prominent features of this pedigree. In the four cases for whom neuropsychometric data were available, verbal memory impairment preceded visual memory deficits; naming was relatively preserved until late in the disease. One of these four cases underwent serial volumetric MRI scans demonstrating in vivo brain tissue loss of 3.9% (38.9 ml, annualized rate of atrophy: 1. 7%) over 22 months of follow-up. The four individuals who had necropsies demonstrated the neuropathological hallmarks of Alzheimer's disease. Apolipoprotein E (APOE) status was assessed in five individuals: the case with the youngest age at onset at 33 years of age was found to be homozygous epsilon4/epsilon4, > 1 SD below the mean age of onset for those of known APOE genotype (36.4 +/- 2.3 years, mean +/- SD), and > 2 SDs below the mean age of onset for the pedigree as a whole (37.4 +/- 1.7 years, mean +/- SD). APOE genotype may therefore modulate age at onset in this pedigree.

Behavioral disturbances without amyloid deposits in mice overexpressing human amyloid precursor protein with Flemish (A692G) or Dutch (E693Q) mutation

The contribution of mutations in the amyloid precursor protein (APP) gene known as Flemish (APP/A692G) and Dutch (APP/E693Q) to the pathogenesis of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis of the Dutch type, respectively, was studied in transgenic mice that overexpress the mutant APP in brain. These transgenic mice showed the same early behavioral disturbances and defects and increased premature death as the APP/London (APP V717I), APP/Swedish (K670N, M671L), and other APP transgenic mice described previously. Pathological changes included intense glial reaction, extensive microspongiosis in the white matter, and apoptotic neurons in select areas of the brain, while amyloid deposits were absent, even in mice over 18 months of age. This contrasts with extensive amyloid deposition in APP/London transgenic mice and less pronounced amyloid deposition in APP/Swedish transgenic mice generated identically. It demonstrated, however, that the behavioral deficiencies and the pathological changes in brain resulting from an impaired neuronal function are caused directly by APP or its proteolytic derivative(s). These accelerate or impinge on the normal process of aging and amyloid deposits per se are not essential for this phenotype.

Glycosylphosphatidylinositol-anchored proteins play an important role in the biogenesis of the Alzheimer's amyloid beta-protein

The Alzheimer's amyloid protein (Abeta) is released from the larger amyloid beta-protein precursor (APP) by unidentified enzymes referred to as beta- and gamma-secretase. beta-Secretase cleaves APP on the amino side of Abeta producing a large secreted derivative (sAPPbeta) and an Abeta-bearing C-terminal derivative that is subsequently cleaved by gamma-secretase to release Abeta. Alternative cleavage of the APP by alpha-secretase at Abeta16/17 releases the secreted derivative sAPPalpha. In yeast, alpha-secretase activity has been attributed to glycosylphosphatidylinositol (GPI)-anchored aspartyl proteases. To examine the role of GPI-anchored proteins, we specifically removed these proteins from the surface of mammalian cells using phosphatidylinositol-specific phospholipase C (PI-PLC). PI-PLC treatment of fetal guinea pig brain cultures substantially reduced the amount of Abeta40 and Abeta42 in the medium but had no effect on sAPPalpha. A mutant CHO cell line (gpi85), which lacks GPI-anchored proteins, secreted lower levels of Abeta40, Abeta42, and sAPPbeta than its parental line (GPI+). When this parental line was treated with PI-PLC, Abeta40, Abeta42, and sAPPbeta decreased to levels similar to those observed in the mutant line, and the mutant line was resistant to these effects of PI-PLC. These findings provide strong evidence that one or more GPI-anchored proteins play an important role in beta-secretase activity and Abeta secretion in mammalian cells. The cell-surface GPI-anchored protein(s) involved in Abeta biogenesis may be excellent therapeutic target(s) in Alzheimer's disease.

Transgenic mice expressing an alpha-secretion mutant of the amyloid precursor protein in the brain develop a progressive CNS disorder

Expression of alpha-secretion mutant APP/RK in mouse brain results in a progressive disorganization of the central nervous system, exemplified by behavioral deficits, premature death and neuropathology. Here we report on the progressive nature of this CNS disorder as indicated by the age dependency of the neophobic reaction in the open-field test. The earlier reported NMDA hypo-sensitivity in the transgenic APP/RK mice is likely to represent a subtle functional disturbance, since no changes in NMDA receptor density or distribution could be detected. None of the typical neuropathological hallmarks of Alzheimer's Disease, i.e. amyloid deposits and neurofibrillary tangles are detected in the brain of these transgenic mice. Nevertheless, the progressive CNS disorder elicited in the transgenic APP/RK mice recapitulates certain features and symptoms of patients with Alzheimer's disease as discussed.

Giant cell arteritis in association with cerebral amyloid angiopathy: immunohistochemical and molecular studies

Giant cell arteritis (GCA) usually manifests as a transmural vascular infiltrate of mononuclear and multinucleated giant cells (MNGC). We describe six patients with GCA associated with severe cerebral amyloid angiopathy (CAA), all with cerebral hemorrhage or varying degrees of cerebral infarct, and histological evidence of Alzheimer's disease (cortical CAA often predominating over senile plaques and neurofibrillary tangles). One case showed mostly cortical involvement (with old microhemorrhages), and the others were primarily leptomeningeal (with involvement of the underlying cortex and extensive encephalomalacia of adjacent brain). Many vessels with CAA exhibited a pronounced adventitial and perivascular infiltrate of lymphocytes, histiocytes, and MNGC. Immunohistochemical staining showed deposition of beta/A4 peptide primarily in the thickened media of CAA vessels, and within the cytoplasm of MNGC--suggesting phagocytosis of insoluble peptide. Cystatin C antibody stained vascular amyloid and diffusely highlighted astrocytic and MNGC cytoplasm. HAM56-positive macrophages were frequently seen around amyloid-laden vessels. Anti-smooth muscle actin immunohistochemistry suggests the occurrence of medial destruction by amyloid, with relative preservation of intimal cells. Ultrastructural studies performed in one case confirmed the presence of intracytoplasmic amyloid in MNGC. The GCA seen in these cases of CAA most likely represents a foreign body response to amyloid proteins, causing secondary destruction of the vessel wall. DNA from brain tissues of five affected patients was examined to assess whether mutations were present in exon 17 of the APP gene or exon 2 of the cystatin C gene, a finding that might explain the foreign body giant cell response to amyloid proteins in these cases. However, restriction fragment mapping of amplified gene segments showed that previously described mutations were not present in these cases.

Neurons and extracellular neurofibrillary tangles in the hippocampal subdivisions in early-onset familial Alzheimer's disease: a case study

We have investigated morphometrically unaffected neurons, intracellular neurofibrillary tangles (I-NFT) and extracellular neurofibrillary tangles (E-NFT) in eight subdivisions of the hippocampal cortex in two cases of early-onset familial Alzheimer's disease (FAD) and six cases of early-onset sporadic Alzheimer's disease (SAD). The hippocampal subdivisions examined included: CA4, CA3, CA2, CA1, prosubiculum, subiculum and presubiculum (PRE), parasubiculum (PARA) and entorhinal cortex (ENT). CA3, CA2 and CA1 in the FAD cases showed more severe neuronal loss and much greater E-NFT formation than in the SAD cases, while ENT in both the FAD cases showed less neuronal loss and less E-NFT formation. These data suggest that the cornu ammonis is affected more severely than the ENT in the FAD cases. These observations indicate that hippocampal pathology in the FAD cases is qualitatively as well as quantitatively different from that in sporadic cases. These results provide further evidence for pathological heterogeneity in AD, although the number of FAD cases examined is very small.

Cerebellar pathology in sporadic and familial Alzheimer's disease including APP 717 (Val-->Ile) mutation cases: a morphometric investigation

Familial Alzheimer's disease (FAD) tends to present with more prominent neurological symptoms including cerebellar signs than sporadic Alzheimer's disease (SAD). In order to elucidate the pathological differences in the cerebellum, which may be associated with the cerebellar symptoms, we have investigated morphometrically beta-amyloid deposits, atrocytosis, Purkinje cells and dentate neurons in the cerebellum of 10 FAD patients including two cases with the beta-amyloid precursor protein (APP) gene mutation (APP717 Val-->Ile), 10 SAD patients and 10 non-demented age-matched controls. The regions examined included the molecular, Purkinje cell and granular cell layers, the cerebellar white matter and the dentate nucleus. Purkinje cell density in FAD was significantly lower than in SAD. There were no significant differences in the density of dentate neurons among the three groups. The density of astrocytes in FAD was significantly greater than that in SAD in the granular cell and Purkinje cell layers and in the white matter. There were no significant differences in the amount and subtypes of beta-amyloid deposits (extracellular, vascular and perivascular) between FAD and SAD in all the regions investigated. In two cases with the APP mutation, both Purkinje cell loss and beta-amyloid deposition in the cerebellum were greater than the mean for FAD and SAD cases. Astrocytosis in the mutation cases was not greater than the mean for FAD cases except for the dentate nucleus in one case. Extracellular beta-amyloid deposits were not seen in any of the control cases although amyloid angiopathy was observed in one case. This study demonstrates for the first time that Purkinje cell loss and reactive astrocytosis of the cerebellum in FAD are more severe than in SAD, but that beta-amyloid deposition in the cerebellum in both FAD and SAD are similar. The more prominent neurological signs observed in FAD may be explained by more severe neurodegeneration than are found in sporadic cases.

Melatonin prevents death of neuroblastoma cells exposed to the Alzheimer amyloid peptide

Studies from several laboratories have generated evidence suggesting that oxidative stress is involved in the pathogenesis of Alzheimer's disease (AD). The finding that the amyloid beta protein (Abeta) has neurotoxic properties and that such effects are, in part, mediated by free radicals has provided insights into mechanisms of cell death in AD and an avenue to explore new therapeutic approaches. In this study we demonstrate that melatonin, a pineal hormone with recently established antioxidant properties, is remarkably effective in preventing death of cultured neuroblastoma cells as well as oxidative damage and intracellular Ca2+ increases induced by a cytotoxic fragment of Abeta. The effects of melatonin were extremely reproducible and corroborated by multiple quantitative methods, including cell viability studies by confocal laser microscopy, electron microscopy, and measurements of intracellular calcium levels. The importance of this finding is that, in contrast to conventional antioxidants, melatonin has a proposed physiological role in the aging process. Secretion levels of this hormone are decreased in aging and more severely reduced in AD. The reported phenomenon may be of therapeutic relevance in AD.

Interfamilial and intrafamilial phenotypic heterogeneity in familial Alzheimer's disease

The features of Alzheimer's disease (AD) are very heterogenous, and some component of the variability of AD is likely to be related to genetic factors. To investigate this question, we evaluated 19 clinical neuropsychiatric and brain imaging features in 32 familial Alzheimer's disease (FAD) kindred, primarily of late onset. Within families, patients displayed a high degree of phenotypic heterogeneity (PH), which occurred irrespective of gender, ethnicity, or apolipoprotein E genotype. Overall, an equivalent amount of PH was observed in both the between- (37%) and within-family (31%) groups. However, for onset age and rate of decline between families, there was greater PH than within families (P = .002 and P = .01, respectively). A similar trend was found for severity of cortical atrophy (P = .05). These observations suggest a weak genetic influence, and possibly strong nongenetic influences, on the degree of phenotypic heterogeneity in late-onset FAD. In early-onset AD kindred, a much smaller degree of phenotypic heterogeneity may be expected within families, because genetic influences in phenotypic expression tend to be more prominent in early-onset cases.

Application of PET in dementia disorders

Positron emission tomography (PET) is a valuable tool for understanding of functional correlates of biological and structural changes in brain of patients with various dementia diseases. As such it can provide valuable physiological correlates important for diagnosis, management and research of dementia disorders. A crucial question is whether PET is capable of early or preclinical detection of dementia. Longitudinal PET studies in Alzheimer families with chromosomal aberrations will be important for. Impairment of cerebral blood flow and glucose metabolism is a common feature in patients with Alzheimer's disease. The pattern of changes is distinct from other forms of dementia and correlates with neuropsychological impairments. Neuroreceptor studies have to be further applied as well as monitoring of drug treatment effects.

Purkinje cell loss and astrocytosis in the cerebellum in familial and sporadic Alzheimer's disease

In order to elucidate further the pathological differences between familial Alzheimer's disease (FAD) and sporadic Alzheimer's disease (SAD), Purkinje cells and astrocytosis in the cerebellum of 10 FAD patients including two cases with the beta-amyloid precursor protein (APP) gene mutation in codon 717 (APP717 Val-->Ile), 10 SAD patients and 10 non-demented, age-matched controls were morphometrically investigated using immunohistochemistry. The regions examined included the molecular, Purkinje cell and granular cell layers, and the cerebellar white matter. This is the first report of a significantly decreased Purkinje cell density in FAD when compared to SAD. The density in SAD was also significantly decreased when compared to controls. In addition, the astrocyte density in FAD was significantly greater than that of SAD in the Purkinje cell layer, granular cell layer, and white matter. The density in SAD was also greater than that in controls, but not significantly in the granular cell layer and white matter. In the cases with the APP717 (Val-->Ile) mutation, Purkinje cell loss in the cerebellum was greater than the mean for FAD and SAD cases, while the astrocyte density was lower than the mean of all FAD cases, but higher than the mean of SAD cases. This study demonstrates that Purkinje cell loss and astrocytosis in FAD in the cerebellum are greater than in SAD, indicating that the cerebellum is more affected in FAD than in SAD.

[Genetics of Alzheimer's disease]

This review reports the different genetic factors that have been identified either as risk factor for Alzheimer's disease (AD) or directly causing the disease. First are reviewed epidemiological data and biological mechanisms about the apoplipoprotein E gene allele epsilon 4 that is a major risk factor for Alzheimer's disease. The second part describes the mutations responsible for early-onset autosomal dominant AD found in three different genes. The gene located on chromosome 21 encodes the amyloid precusor protein (APP). The presenilin 1 and presenilin 2 genes, located on chromosome 14 and 1 respectively, encode not yet known membrane proteins.

Atrophy of the hippocampal formation in early familial Alzheimer's disease. A longitudinal MRI study of at-risk members of a family with an amyloid precursor protein 717Val-Gly mutation

The hippocampal formation (HF) is known from pathological and magnetic resonance imaging (MRI) studies to become severely atrophied in established Alzheimer's disease (AD). This study examined whether changes in the HF could also be detected in very early AD by scanning subjects at risk of developing familial AD (FAD). Five at risk members of a pedigree with the amyloid precursor protein (APP) 717 valine to glycine mutation underwent serial MRI scanning with volumetric measurement of the HF as well as neurological and neuropsychological assessments. Over a period of two years two subjects became clinically affected, a loss of up to 20% of the volume of the HF occurred in the two years over which symptoms first appeared. Asymmetrical HF atrophy was shown to have been present before the development of overt symptoms. This may have important implications for early diagnosis in AD more generally.

Clinical and neuroimaging features of familial Alzheimer's disease

Subtle phenotypic differences between familial Alzheimer's disease (FAD) pedigrees can be identified which may reflect the genetic and allelic heterogeneity of the disease. Positron emission tomography (PET) of APP mutation and chromosome 14-linked FAD pedigree members reveals biparietal bitemporal hypometabolism. Scanning of asymptomatic at-risk individuals reveals a similar, but quantitatively less severe, pattern of hypometabolism.

Genetic dissection of Alzheimer disease, a heterogeneous disorder

The genetics of Alzheimer disease (AD) are complex and not completely understood. Mutations in the amyloid precursor protein gene (APP) can cause early-onset autosomal dominant AD. In vitro studies indicate that cells expressing mutant APPs overproduce pathogenic forms of the A beta peptide, the major component of AD amyloid. However, mutations in the APP gene are responsible for 5% or less of all early-onset familial AD. A locus on chromosome 14 is responsible for AD in other early-onset AD families and represents the most severe form of the disease in terms of age of onset and rate of decline. Attempts to identify the AD3 gene by positional cloning methods are underway. At least one additional early-onset AD locus remains to be located. In late-onset AD, the apolipoprotein E gene allele epsilon 4 is a risk factor for AD. This allele appears to act as a dose-dependent age-of-onset modifier. The epsilon 2 allele of this gene may be protective. Other late-onset susceptibility factors remain to be identified.

Evidence that the APOE locus influences rate of disease progression in late onset familial Alzheimer's Disease but is not causative

An association has been observed in several independent data sets between late onset Alzheimer's Disease (AD) and the APOE locus on chromosome 19. We have examined the genotype in family history positive (FHP) and family history negative (FHN) cases and find a distortion of the APOE allele frequencies in accord with previous studies. However, when we examined the allele distribution of the at-risk siblings of the FHP group we found an excess of the epsilon 4 allele which also differs significantly from historic controls but not from the affected siblings. The age distribution of the affected and unaffected siblings was similar, suggesting that the allelic frequency distortion in the unaffected siblings was not due to their being below the mean age of onset. Lod score linkage analysis, with age dependent onset and non-stringent specification of the genetic parameters, did not suggest linkage to the APOE locus. Furthermore, an analysis of variance of the age of disease free survival suggested that APOE genotype contributes a small fraction of the total variance indicating that the APOE locus is a poor predictor of disease free survival age within late onset families. One explanation for the age dependent association reported by other groups, and our results, is that the APOE locus enhances the rate of progression of the disease process in otherwise predisposed individuals and that variation at this locus is not able in and of itself to cause the disease. We suggest this hypothesis is compatible with the current literature regarding APOE and AD.

Clinical features of early onset, familial Alzheimer's disease linked to chromosome 14

Early onset familial Alzheimer's disease (AD) has an autosomal dominant mode of inheritance. Two genes are responsible for the majority of cases of this subtype of AD. Mutations in the beta-amyloid precursor protein (beta APP) gene on chromosome 21 have been shown to completely cosegregate with the disease. We and others have previously described the clinical features of families with beta APP mutations at the codon 717 locus in an attempt to define the phenotype associated with a valine to isoleucine (Val-->Ile) or a valine to glycine (Val-->Gly) change. More recently, a second locus for very early onset disease has been localized to chromosome 14. The results of linkage studies in some families suggesting linkage to both chromosomes have been explained by the suggestion of a second (centromeric) locus on chromosome 21. Here we report the clinical features and genetic analysis of a British pedigree (F74) with early onset AD in which neither the beta APP locus nor any other chromosome 21 locus segregates with the disease, but in which good evidence is seen for linkage on the long arm of chromosome 14. In particular we report marker data suggesting that the chromosome 14 disease locus is close to D14S43 and D14S77. Given the likelihood that F74 represents a chromosome 14 linked family, we describe the clinical features and make a limited clinical comparison with the beta APP717 Val-->Ile and beta APP717 Val-->Gly encoded families that have been previously described.(ABSTRACT TRUNCATED AT 250 WORDS)

A large pedigree with early-onset Alzheimer's disease: clinical, neuropathologic, and genetic characterization

We present clinical, neuropsychological, and neuropathologic data on a large pedigree including 34 subjects with early-onset progressive dementia. The mean (+/- SD) age at onset was 46 +/- 3.5 years and the mean age at death 52.6 +/- 5.7 years. Twelve patients were clinically diagnosed as having probable Alzheimer's disease (AD) according to the NINCDS-ADRDA criteria. Neuropsychological evaluation, performed at a moderate stage of the disease, was available in six subjects and showed a classic pattern of cognitive deficit. Myoclonus and extrapyramidal signs were common, and seizures were present in all affected subjects. There were neuropathologic changes typical of AD in two brains. A significant lod score of 5.48 was observed at a recombination fraction of theta = 0.0 with the genetic marker D14S43, thereby establishing that the responsible gene was located on chromosome 14q24.3. These results suggest that epilepsy could represent a particular feature in AD families linked to chromosome 14q.

Chromosome 14-encoded Alzheimer's disease: genetic and clinicopathological description

A family of Finnish descent with very-early-onset Alzheimer's disease has been identified. Genetic analysis of this family eliminated the amyloid precursor protein gene as the pathogenic locus, but strongly implicated a locus on chromosome 14q23.4 between D14S52 and D14S55. The early age at onset of the disease (average, 36 years; range, 35-39 years), the rapid progression, and the early and prominent myoclonus, while they appear to be frequent findings in the chromosome 14-encoded form of Alzheimer's disease, raised the clinical suspicion of prion disease. However, sequencing the prion gene-coding region of 2 affected members of the pedigree failed to show any abnormality. Apart from the presence of modest cortical vacuolar change, the pathological features of our index patient appeared typical of Alzheimer's disease with abundant senile plaques immunoreactive with beta-amyloid, but not with prion protein antibodies.

Phenotype of chromosome 14-linked familial Alzheimer's disease in a large kindred

We report the clinical and neuropathological features of chromosome 14-linked familial Alzheimer's disease (14qFAD) in affected members of the L family. Some clinical information on all 16 known affected individuals and detailed neuropathological findings in 6 family members were available for review. Common features of the phenotype of 14qFAD in the L family included onset of dementia before the age of 50, early progressive aphasia, early-appearing myoclonus and generalized seizures, paratonia, cortical atrophy, numerous and extensive senile plaques and neurofibrillary tangles, and prominent amyloid angiopathy. Descriptions of phenotypic features were available for six additional recently defined 14q-linked FAD kindreds: the findings in four of them (FAD4, FAD2, A, B) indicated a relatively consistently shared 14qFAD phenotype, conforming closely with the specific clinical and neuropathological characteristics noted in the L family. Comparisons also suggested several ostensible phenotypic variants in 14qFAD: (1) In two 14q-linked kindreds (SNW/FAD3, FAD1), affected individuals in some instances were noted to survive to age 70 or beyond and the mean age at onset (> 49 years) in these two kindreds was somewhat higher than in their five 14qFAD counterparts (< 48 years in each); (2) in the SNW/FAD3 kindred, seizures and myoclonus were absent in all 10 subjects examined; and (3) cerebellar amyloid plaques were variably present within and among several 14qFAD kindreds. Comparisons with phenotypic features recently detailed in three kindreds (TOR3, F19, ROM) with codon 717 amyloid precursor protein gene mutations (i.e., APP717 FAD) suggested several distinctions: Prominent progressive aphasia, myoclonus, seizures, and paratonia were all apparently less prevalent in APP717 FAD, with language function predominantly spared over the initial disease course. The extent of homogeneity and heterogeneity in the clinical and neuropathological phenotype of 14q-linked FAD and its possible meaningful distinctions from the phenotypes of APP717 FAD await further determination.

The earliest cognitive change in a person with familial Alzheimer's disease: presymptomatic neuropsychological features in a pedigree with familial Alzheimer's disease confirmed at necropsy

Comprehensive, longitudinal neuropsychological assessments are reported in a person "at risk" from autosomal dominant, necropsy confirmed familial Alzheimer's disease. The first assessment showed a moderately selective verbal memory deficit in the context of mild general intellectual impairment. Subsequent testing showed the progressive deterioration of visual memory and a mild decline of perceptual and spatial skills. Language and literacy skills, however, remained comparatively intact. The neuropsychological profiles obtained at each assessment are presented in profile maps. These permit direct longitudinal comparison of cognitive function, and may serve in the comparison of different potential cases of familial Alzheimer's disease. This case sought medical attention for memory difficulties 26 months after the first neuropsychological assessment. These results mark the first cognitive manifestations in a pedigree with familial Alzheimer's disease which, in this case, were seen presymptomatically. The findings are discussed in relation to neuropsychological studies of affected cases, and in terms of their reflecting the heterogeneous nature of familial Alzheimer's disease.

The molecular genetics of Alzheimer's disease

The major pathological characteristic of Alzheimer's disease (AD) is the abnormal deposition of beta-amyloid peptide (A beta) in the brain. In some early onset cases, the disease develops because of mutations in the gene coding for beta-amyloid precursor protein (beta APP). However, the majority of AD families in the early onset subgroup are linked to a locus on chromosome 14. The genetic analysis and age of onset correlates of both the beta APP gene and the chromosome 14 locus are discussed. We speculate on the mechanisms by which the beta APP mutations cause the disease and discuss recent advances in beta APP processing that may be relevant to the pathogenesis of the late-onset (common) form of the disease. In addition, we review the association of the APOE locus with late-onset familial and nonfamilial disease. Further work is required to establish the effects of this locus on disease occurrence, age of onset, and progression. The molecular pathology of ApoE in relation to AD development and the identification of the chromosome 14 gene will greatly contribute to a general pathogenic model of AD, and will clarify the role of beta APP and its derivatives.

Frontal lobe dementia is not a variant of prion disease

Frontal lobe dementia (FLD) is a syndromal diagnosis with a variable pathology. It has been argued that FLD is a dementing disorder which should be nosologically and etiologically distinguished from other types of dementia. However, similarities with prior disease and Alzheimer's disease have led to the suggestion that FLD is a variant of one or other of these dementias. We have tested this line of argument by examining the frontal cortex and cerebellum of 14 FLD cases and probing the molecular pathology using well characterized antibodies to prion protein and beta-amyloid protein. No prion protein deposits or significant levels of beta-amyloid protein were detected. FLD is a dementing disorder whose molecular pathology, whilst as yet uncharacterised, can be distinguished from those of other dementing disorders.

Molecular genetics in neurology

There has been remarkable progress in the identification of mutations in genes that cause inherited neurological disorders. Abnormalities in the genes for Huntington disease, neurofibromatosis types 1 and 2, one form of familial amyotrophic lateral sclerosis, fragile X syndrome, myotonic dystrophy, Kennedy syndrome, Menkes disease, and several forms of retinitis pigmentosa have been elucidated. Rare disorders of neuronal migration such as Kallmann syndrome, Miller-Dieker syndrome, and Norrie disease have been shown to be due to specific gene defects. Several muscle disorders characterized by abnormal membrane excitability have been defined as mutations of the muscle sodium or chloride channels. These advances provide opportunity for accurate molecular diagnosis of at-risk individuals and are the harbinger of new approaches to therapy of these diseases.

Clinical studies in Alzheimer patients with positron emission tomography

Brain imaging techniques will in the future play an important role in the assessment of patients with neurogenerative disorders such as Alzheimer's disease (AD). An early diagnosis of AD is today hampered by lack of reliable diagnostic markers. Positron emission tomography (PET) permits the quantification and three-dimensional imaging of physiological variables. This provides the clinician with a non-invasive imaging technique which allows in vivo quantification of physiological processes in AD underlying dysfunction of cognition. PET studies regarding changes in cerebral blood flow and metabolism are rather consistent at least in moderate/advanced cases of AD. How early in the progress of the disease deficits in these parameters can be observed is still an open question. Longitudinal studies will here be important and especially in individuals with a family history of AD. Since deficits in cholinergic neurotransmission have been measured in autopsy AD brains attempts have also been made to visualized cholinergic activity in vivo. Nicotinic and muscarinic receptors have been visualized in normal and AD brains. A reduced uptake and binding of [11C]nicotine in the temporal and frontal cortices have been measured in AD patients by PET. Few treatment studies in AD have been evaluated by PET. Long-term treatment with the cholinesterase inhibitor tacrine increase the uptake of [11C]nicotine. Significant reduction in uptake between the two enantiomers (S)(-) and (R)(+)-[11C]nicotine has been observed compatible with a restoration of nicotinic receptors. Tacrine also significantly increased the glucose metabolism. PET studies indicate that long-term tacrine treatment in AD patients with mild dementia improves functional activities in brain. When an AD patient with moderate dementia was treated with nerve growth factor (NGF) PET studies revealed increase in cortical blood flow and nicotinic receptors. PET studies will in the future play an important role in the evaluation of new therapeutic drug strategies in AD.

Alzheimer's disease families with amyloid precursor protein mutations

Early onset Familial Alzheimer's Disease (FAD) is an autosomal dominant disease with apparent complete penetrance. It is genetically heterogeneous with some families carrying mutations in the amyloid precursor protein (APP) gene which segregate with the disease. In addition, there is allelic heterogeneity with four mutations associated with FAD. Three mutations have been reported at APP 717, just distal to the C-terminus of the beta-amyloid domain, APP 717 val-ile, APP 717 val-phe, and APP 717 val-gly, which are associated with autopsy-proven Alzheimer's disease (AD). APP 670/671 lies at the N terminus of the beta-amyloid domain and is associated with clinically diagnosed FAD in two Swedish families. FAD tends to have prominent myoclonus and this is shared by the cases with APP mutations. In two unrelated UK families with APP 717 val-ile mutations there was early prominent memory impairment with dyscalculia proceeding to generalized cognitive impairment with a lack of insight. There was a late development of a gait disturbance with extrapyramidal features in some members. Positron emission tomography (PET) with fluorodeoxyglucose demonstrated posterior bitemporal biparietal hypometabolism in one case. Magnetic resonance imaging (MRI) showed generalized cerebral atrophy particularly affecting the temporal lobes and hippocampus. At autopsy, a single case showed extensive beta-amyloid deposition with congophilic angiopathy and widespread senile plaques and neurofibrillary tangles. The cytoskeletal pathology associated with abnormally phosphorylated tau was similar to cases of sporadic AD. In addition, there were widespread cortical and subcortical Lewy bodies. A single family with the APP 717 val-gly mutation also showed prominent myoclonus, lack of insight, and seizures, PET, in a single case, showed classical biparietal bitemporal hypometabolism. Autopsy, in a single case, showed diffuse deposits of beta-amyloid throughout the cortex with frequent neuritic plaques and neurofibrillary tangles. No other inclusion bodies were seen. There was severe congophilic angiopathy. The age at onset of APP mutations is around 50 years of age by contrast to other early onset FAD pedigrees.

Molecular pathology of Alzheimer's disease

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