Causative and susceptibility genes for Alzheimer's disease: a review
ABSTRACT Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.
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- "To adapt to environmental changes and survive different types of injuries, as in the case of acute or chronic stress, exposed cells are continually challenged to activate integrated survival responses (Bullock and Hammond, 2003). One of these, the heat shock response actively operate in the optic cell system, under control of redox regulated gene network, the vitagene network, recognized to be critical for the intracellular chaperoning function which is essential for the proper folding of misfolded or mutated proteins, thereby protecting vulnerable cells from death (Selkoe, 2001; Rocchi et al., 2003; Guo et al., 2006). As stress inducible proteins, chaperones help the correct folding and maintenance of the proper conformation of essential proteins, thus promoting cell survival in all those pathological conditions associated oxidative stress (Hirota et al., 2002; Calabrese et al., 2010c). "
ABSTRACT: Amyloid deposits, constituted of amyloid beta (Aβ) aggregates, are a characteristic feature of several neurodegenerative diseases, such as Alzheimer's, mild cognitive impairment and Parkinson's disease. They also have been recently implicated in the pathogenesis of retinal damage, as well as age-related macular degeneration and glaucoma. Glaucoma is a progressive optic neuropathy characterized by gradual degeneration of neuronal tissue due to retinal ganglion cell loss, associated to visual field loss over time resulting in irreversible blindness. Accumulation of Aβ characterizes glaucoma as a protein misfolding disease, suggesting a pathogenic role for oxidative stress in the pathogenesis of retinal degenerative damage associated to glaucoma. There is a growing body of evidence demonstrating a link between Alzheimer's disease and glaucoma. Further, several heat shock proteins (HSPs) members have been implicated both in neurodegenerative diseases and glaucomatous apoptosis. To maintain redox homeostasis vitagenes, as integrated mechanisms, operate actively to preserve cell survival under condition of stress. Vitagenes encode for sirtuin, thioredoxin and HSPs. The present study was designed to investigate cellular stress response mechanisms in the blood of patients with glaucoma, compared to control subjects. Levels of vitagenes HSP-72, heme oxygenase-1, as well as F2-isoprostanes were significantly higher in the blood of patients with glaucoma than in controls. Furthermore, in the same experimental group increased expression of Trx and sirtuin 1 were measured. Our results sustain the importance of redox homeostasis disruption in the pathogenesis of glaucoma and highlights the opportunity that new therapies that prevents neurodegeneration through non-immunomodulatory mechanisms might be synergistically associated with current glaucoma therapies, thus unraveling important targets for novel cytoprotective strategies.Frontiers in Pharmacology 06/2014; 5:129. DOI:10.3389/fphar.2014.00129
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- "An insertion or deletion early in the sequence of a gene results in a more altered protein, which could be abnormally short or long and most likely nonfunctional [Van Den Hurk et al. 2001]. Generally, mutations in the APP gene account for approximately 5 % of familial AD, with a disease onset age of 65 [Rocchi et al. 2003]. In our study, we show that the frequency of frameshift mutations in exons 16 and 17 of the APP gene is 87 % (7 out 8 cases) within familial AD cases, whereas the frequency of mutations in exon 17 is 12 % (2 out of 17 cases) within sporadic AD cases. "
ABSTRACT: In Morocco, Alzheimer's disease (AD) affects almost 30,000 individuals, and this number could increase to 75,000 by 2020. To our knowledge, the genes predisposing individuals to AD and predicting disease incidence remain elusive. In this study, we aimed to evaluate the genetic contribution of mutations in the amyloid precursor protein (APP) gene exons 16 and 17 to familial and sporadic AD cases. Seventeen sporadic cases and eight family cases were seen at the memory clinic of the University of Casablanca Neurology Department. These patients underwent standard somatic neurological examination, cognitive function assessment, brain imaging, and laboratory tests. Direct sequencing of exons 16 and 17 of the APP gene was performed on genomic DNA of AD patients. In this original Moroccan study, we identified seven novel frameshift mutations in exons 16 and 17 of the APP gene. Interestingly, only one novel splice mutation was detected in a family case. There is a strong correlation between clinical symptoms and genetic factors in Moroccan patients with a family history of AD. Therefore, mutations in APP gene exons 16 and 17 may eventually become genetic markers for AD predisposition.Journal of Molecular Neuroscience 03/2014; DOI:10.1007/s12031-014-0278-7 · 2.76 Impact Factor
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- "However, familial cases usually have an earlier age of onset and show an autosomal-dominant pattern of inheritance with virtually complete penetrance linked to mutations in the β-amyloid precursor protein (APP) or presenilins genes. Genetic defects may result in overproduction of amyloid β (Aβ) or in the generation of mutated Aβ forms with a greater propensity for aggregation (Rocchi et al., 2003). "
ABSTRACT: Although Alzheimer's disease (AD) is usually sporadic, in a small proportion of cases it is familial and can be linked to mutations in β-amyloid precursor protein (APP). Unlike the other genetic defects, the mutation [alanine-673->valine-673] (A673V) causes the disease only in the homozygous condition with enhanced amyloid β (Aβ) production and aggregation; heterozygous carriers remain unaffected. It is not clear how misfolding and aggregation of Aβ is affected in vivo by this mutation and whether this correlates with its toxic effects. No animal models over-expressing the A673V-APP gene or alanine-2-valine (A2V) mutated human Aβ protein are currently available. Using the invertebrate Caenorhabditis elegans, we generated the first transgenic animal model to express the human Aβ1-40 wild-type (WT) in neurons or possess the A2V mutation (Aβ1-40A2V). Insertion of an Aβ-mutated gene into this nematode reproduced the homozygous state of the human pathology. Functional and biochemical characteristics found in the A2V strain were compared to those of transgenic C. elegans expressing Aβ1-40WT. The expression of both WT and A2V Aβ1-40 specifically reduced the nematode's lifespan, causing behavioral defects and neurotransmission impairment which were worse in A2V worms. Mutant animals were more resistant than WT to paralysis induced by the cholinergic agonist levamisole, indicating that the locomotor defect was specifically linked to postsynaptic dysfunctions. The toxicity caused by the mutated protein was associated with a high propensity to form oligomeric assemblies which accumulate in the neurons, suggesting this to be the central event involved in the postsynaptic damage and early onset of the disease in homozygous human A673V carriers.Neurobiology of Disease 10/2013; 62(100). DOI:10.1016/j.nbd.2013.10.024 · 5.20 Impact Factor