Genetic factors in Alzheimer's disease: a review of recent advances

A Review of the Current Mammalian Models of Alzheimer's Disease and Challenges That Need to Be Overcome

Alzheimer's disease (AD) is one of the looming health crises of the near future. Increasing lifespans and better medical treatment for other conditions mean that the prevalence of this disease is expected to triple by 2050. The impact of AD includes both the large toll on individuals and their families as well as a large financial cost to society. So far, we have no way to prevent, slow, or cure the disease. Current medications can only alleviate some of the symptoms temporarily. Many animal models of AD have been created, with the first transgenic mouse model in 1995. Mouse models have been beset by challenges, and no mouse model fully captures the symptomatology of AD without multiple genetic mutations and/or transgenes, some of which have never been implicated in human AD. Over 25 years later, many mouse models have been given an AD-like disease and then 'cured' in the lab, only for the treatments to fail in clinical trials. This review argues that small animal models are insufficient for modelling complex disorders such as AD. In order to find effective treatments for AD, we need to create large animal models with brains and lifespan that are closer to humans, and underlying genetics that already predispose them to AD-like phenotypes.

Clinical and neuropathological features of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is an increasingly recognized entity which overlaps in clinical, pathological and genetic features with Alzheimer's (AD) and Parkinson's disease (PD). Clinically, it is characterized by progressive cognitive impairment with significant fluctuations in alertness, parkinsonism, and psychosis with recurrent hallucinations. The neuropathological hallmarks are the intracytoplasmic inclusions in substantia nigra typical of PD, known as Lewy bodies (LB), but widely distributed throughout paralimbic and neocortical regions. Most of the cases also coexist with a plaque predominant AD. The evidence of alpha-synuclein in LB and related neurites as well as of a synuclein fragment in AD plaques opens new links among these neurodegenerative diseases. This article will review briefly the clinical and pathologicalfeatures that DLB shares with AD and PD, as well as those that support the idea that it is a distinct disorder.

Selective familiarity deficits in otherwise cognitively intact aging individuals with genetic risk for Alzheimer's disease

Introduction

Familiarity has been associated with integrity of the rhinal cortex. Thus, impairment in familiarity is expected in very early stages of Alzheimer's disease (AD). The apolipoprotein E (APOE) ε4 allele is a major risk factor for AD. Here, we investigated the effect of the APOE ε4 status on familiarity in cognitively normal aging individuals.

Methods

Eighty-one individuals aged between 55 and 80 years, 21 carriers and 60 noncarriers, were used in these analyses. A cognitive evaluation was performed on all participants to document the absence of objective cognitive deficits. The effect of APOE ε4 status on familiarity was tested using independent sample t test and an analysis of covariance controlling for age, gender, and education.

Results

The groups did not differ in term of age, education, and male/female ratio. APOE ε4 carriers showed a significant reduction in familiarity. No other cognitive deficit was observed in the group of ε4 carriers, relative to noncarriers.

Discussion

APOE ε4 is associated with a reduction in familiarity in the absence of other cognitive deficits. These results suggest that performance in familiarity could represent an early cognitive marker for individuals at risk of AD.

What is Your Risk of Contracting Alzheimer's Disease? A Telematics Tool Helps you to Predict it

Alzheimer's disease (AD) is the most common dementia in developed countries. Between the identified risk factors, one of the most important is the age. Its prevalence reaches 24 % in men and 33 % in women over 85 years. Increase in life expectancy, making it a serious public health problem. Prevention of Alzheimer's disease represents a major challenge to health. Given that Alzheimer's disease is largely dependent on the genetics of each person and uninterrupted progress of the age, which is try to make people aware that there are other factors that can alter your chance of developing the Alzheimer disease and although currently not reduce, help is not increased in the near or distant future.The aim of this paper is to develop and evaluate a Web-Mobile application (Alzhe Alert) used to calculate the risk of Alzheimer's from a short questionnaire using a computer or mobile device, so that any user, without requiring computer skills, can access the website to estimate their risk of developing the disease in the coming years depending on their habits and daily basis activities. The users who have realized the questionnaire can to observe in a graph the result, and they will know which is at risk for Alzheimer's at present and over the next 50 years if they continue with the same habits and lifestyle. The objective is that the users can be aware of the risk they have different habits of life about their health. Currently, 243 users (84 women and 159 men) of white race have completed the questionnaire. 76 % of the users have got a risk below the average.

Genetic Factors Affecting Late-Onset Alzheimer's Disease Susceptibility

Alzheimer's disease is considered a progressive brain disease in the older population. Late-onset Alzheimer's disease (LOAD) as a multifactorial dementia has a polygenic inheritance. Age, environment, and lifestyle along with a growing number of genetic factors have been reported as risk factors for LOAD. Our aim was to present results of LOAD association studies that have been done in northwestern Iran, and we also explored possible interactions with apolipoprotein E (APOE) status. We re-evaluated the association of these markers in dominant, recessive, and additive models. In all, 160 LOAD and 163 healthy control subjects of Azeri Turkish ethnicity were studied. The Chi-square test with Yates' correction and Fisher's exact test were used for statistical analysis. A Bonferroni-corrected p value, based on the number of statistical tests, was considered significant. Our results confirmed that chemokine receptor type 2 (CCR2), estrogen receptor 1 (ESR1), toll-like receptor 2 (TLR2), tumor necrosis factor alpha (TNF α), APOE, bridging integrator 1 (BIN1), and phosphatidylinositol-binding clathrin assembly protein (PICALM) are LOAD susceptibility loci in Azeri Turk ancestry populations. Among them, variants of CCR2, ESR1, TNF α, and APOE revealed associations in three different genetic models. After adjusting for APOE, the association (both allelic and genotypic) with CCR2, BIN1, and ESRα (PvuII) was evident only among subjects without the APOE ε4, whereas the association with CCR5, without Bonferroni correction, was significant only among subjects carrying the APOE ε4 allele. This result is an evidence of a synergistic and antagonistic effect of APOE on variant associations with LOAD.

Apolipoprotein E gene polymorphism and Alzheimer's disease in Chinese population: a meta-analysis

The relationship between Apolipoprotein E (ApoE) genotype and the risk of Alzheimer's disease (AD) is relatively well established in Caucasians, but less established in other ethnicities. To examine the association between ApoE polymorphism and the onset of AD in Chinese population, we searched the commonly used electronic databases between January 2000 and November 2013 for relevant studies. Total 20 studies, including 1576 cases and 1741 controls, were retrieved. The results showed statistically significant positive association between risk factor ε4 allele carriers and AD in Chinese population (OR = 3.93, 95% CI = 3.37-4.58, P < 0.00001). Genotype ApoE ε4/ε4 and ε4/ε3 have statistically significant association with AD as well (ε4/ε4: OR = 11.76, 95% CI = 6.38-21.47, P < 0.00001; ε4/ε3: OR = 3.08, 95% CI = 2.57-3.69, P < 0.00001). Furthermore, the frequency of the ApoE ε3 is lower in AD than that in the health controls, and the difference of ε3 allele is also statistically significant (OR = 0.42, 95% CI = 0.37-0.47, P < 0.00001). No significant heterogeneity was observed among all studies. This meta-analysis suggests that the subject with at least one ApoE ε4 allele has higher risk suffering from AD than controls in Chinese population. The results also provide a support for the protection effect of ApoE ε3 allele in developing AD.

Disorders of higher gaze control

The neural centers in the cerebral hemispheres, both cortex and basal ganglia, involved in the generation of saccadic and smooth pursuit eye movements have been well delineated in terms of their location and function. For the generation of saccades these include the frontal eye fields, the supplementary eye field, and the intraparietal sulcus, and in the basal ganglia the caudate nucleus and the substantia nigra, pars compacta. The generation of pursuit eye movements involves the middle temporal (area V5) and medial superior temporal areas and the frontal eye field. These centers and their connections are disturbed not only in acute and chronic lesions such as cerebral infarction, but also in a wide variety of neurodegenerative diseases. In certain of these conditions, such as patients with cortical dementias and basal ganglia disorders, correct interpretation of the resulting eye movement abnormalities can contribute to differentiating between a range of differential diagnoses.

Genetic aspects of Alzheimer disease

Alzheimer disease is the most common cause of dementia and represents a major public health problem. The neuropathologic findings of amyloid-beta plaques and tau containing neurofibrillary tangles represent important molecular clues to the underlying pathogenesis. Genetic factors are well recognized, but complicated. Three rare forms of autosomal-dominant early-onset familial Alzheimer disease have been identified and are associated with mutations in amyloid precursor protein, presenilin 1, and presenilin 2 genes. The more common late-onset form of Alzheimer disease is assumed to be polygenic/multifactorial. However, thus far the only clearly identified genetic risk factor for Alzheimer disease is Apo lipoprotein E. The epsilon4 allele of Apo lipoprotein E influences age at onset of Alzheimer disease, but is neither necessary nor sufficient for the disease. The search continues for the discovery of additional genetic influences.

Neuroprotective and neurotoxic properties of glial cells in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects more than 18 million people worldwide and is characterized by progressive memory deficits, cognitive impairment and personality changes. The main cause of AD is generally attributed to the increased production and accumulation of amyloid-β (Aβ), in association with neurofibrillary tangle (NFT) formation. Increased levels of pro-inflammatory factors such as cytokines and chemokines, and the activation of the complement cascade occurs in the brains of AD patients and contributes to the local inflammatory response triggered by senile plaque. The existence of an inflammatory component in AD is now well known on the basis of epidemiological findings showing a reduced prevalence of the disease upon long-term medication with anti-inflammatory drugs, and evidence from studies of clinical materials that shows an accumulation of activated glial cells, particularly microglia and astrocytes, in the same areas as amyloid plaques. Glial cells maintain brain plasticity and protect the brain for functional recovery from injuries. Dysfunction of glial cells may promote neurodegeneration and, eventually, the retraction of neuronal synapses, which leads to cognitive deficits. The focus of this review is on glial cells and their diversity properties in AD.

Glucose metabolism in early onset versus late onset Alzheimer's disease: an SPM analysis of 120 patients

The aims of this cross-sectional study were (i) to compare the overall glucose metabolism between early onset and late onset Alzheimer's disease in a large sample of patients; and (ii) to investigate the pattern of glucose metabolism as a function of dementia severity in early onset versus late onset Alzheimer's disease, using a statistical parametric mapping (SPM) analysis. Subjects consisted of four groups: 74 patients with early onset Alzheimer's disease, 46 patients with late onset of the disease, and two control groups age matched to each patient group. All the subjects underwent 2-[(18)F]fluoro-2-deoxy-d-glucose (FDG)-PET under the same scanning conditions. Severity of dementia was rated with the Clincial Dementia Rating (CDR). Voxel-based SPM99 was used for statistical analyses. Overall glucose hypometabolism of early onset Alzheimer's disease patients was much greater in magnitude and extent than that of late onset patients, though both groups were similar in dementia severity: the early onset group showed more severe hypometabolism in parietal, frontal and subcortical (basal ganglia and thalamus) areas. When the decline of glucose metabolism was compared as a function of CDR stage, the slope was steeper in early onset than in late onset Alzheimer's disease. The rapid decline occurred at CDR 0.5-1 in the early onset group, whereas similar changes occurred at CDR 2-3 in the late onset group. The greater hypometabolism in early onset than in late onset patients is required to reach the same severity of dementia, probably reflecting greater functional reserve in younger than in older subjects. Alternatively, the metabolic decline curve suggests that the early onset patients may take a more rapid course in the reduction of glucose metabolism than the late onset patients.

Cerebrovascular effects of amyloid-beta peptides: mechanisms and implications for Alzheimer's dementia

1. The amyloid B-peptide (AB) is involved in the mechanisms of Alzheimer dementia. This paper reviews experimental evidence indicating that AB exerts profound effects on the regulation of the cerebral circulation. 2. Thus, AB compromises the ability of cerebral endothelial cells to produce vascular relaxing factors, impairs the ability of cerebral blood vessels to maintain adequate flow during hypotension, and attenuates the increases in CBF evoked by enhanced brain activity. 3. Studies in transgenic mice overexpressing the amyloid precursor protein suggest that these cerebrovascular alterations disrupt the delicate balance between the brain's energy requirements and cerebral blood supply, rendering the brain more vulnerable to ischemic injury. 4. The findings support the recently emerged notion that vascular factors play a pathogenic role in the early stages of Alzheimer dementia.

A multistate model of the genetic risk of Alzheimer's disease

The risk of Alzheimer's disease (AD) increases rapidly with age. It is not clear whether this increase continues at the very oldest ages. A slowing of the rate of increase in risk could result from heterogeneity associated with genetic or other risk factors. This study models explicitly the effect of heterogeneity of risk on the age pattern of incidence of AD. The model is fitted to published data from five prevalence studies and nine studies of AD risk by genotype for the apolipoprotein-E (APOE) gene. The model suggests that the prevalence of AD among white males at age 100 is 41.5%. Heterogeneity in the risk of AD causes the incidence rate to level off at about 11.7% per year at age 102. Some of the heterogeneity of risk is due to differences by APOE genotype. The model estimates that at age 80, the epsilon3/4 genotype is associated with an incidence rate 3.40 times that of those with the epsilon3/3 genotype. The epsilon4/4 genotype is associated with a relative risk of 9.4. Carriers of the epsilon2 allele have a risk that is only 43% of the risk among the epsilon3/3. There is substantial variation in risk associated with unobserved risk factors. Within each APOE genotype, the coefficient of variation of risk is about 1.09. In addition, the model estimates that about 0.20% of the population carries genes that cause AD at very early ages, through mechanisms that are not associated with the APOE genotype.

Alterations in cerebral blood flow and glucose utilization in mice overexpressing the amyloid precursor protein

We have used quantitative autoradiographic techniques to study the relationship between cerebral blood flow (CBF) and glucose utilization (CGU) in two lines of transgenic mice overexpressing Swedish mutant amyloid precursor protein (APP) and APP-derived Abeta peptides. Mice were studied at an age when there are no amyloid plaques. In the 2123 line, CBF was reduced only in telencephalic regions with no corresponding decrease in CGU. In 2576 transgenics, a line with higher levels of Abeta peptide, both CBF and CGU were reduced throughout the brain. The data indicate that Abeta induces alterations in resting CBF that are either associated with or independent of alterations in CGU and that occur in the absence of amyloid deposition in neuropil of blood vessels. These observations support the hypothesis that cerebrovascular and metabolic abnormalities are early events in the pathogenesis of Alzheimer's disease.

A beta-peptides enhance vasoconstriction in cerebral circulation

Amyloid-beta (A beta)-peptides are involved in the pathophysiology of Alzheimer's dementia. We studied the effects of A beta on selected constrictor responses of cerebral circulation. Mice were anesthetized (by using urethane-chloralose) and equipped with a cranial window. Arterial pressure and blood gases were monitored and controlled. Cerebral blood flow (CBF) was monitored by a laser Doppler probe. Topical superfusion with A beta 1-40 (0.1-10 microM), but not with the reverse peptide A beta 40-1, reduced resting CBF (-29 +/- 4% at 5 microM; P < 0.05) and augmented the reduction in CBF produced by the thromboxane analog U-46619 (+45 +/- 3% at 5 microM; P < 0.05). A beta 1-40 or A beta 1-42 did not affect the reduction in CBF produced by hypocapnia. The reduction in resting CBF and the enhancement of vasoconstriction were reversed by treatment with the free radical scavengers superoxide dismutase or manganic(I-II)meso-tetrakis(4-benzoic acid)porphyrin. Substitution of the methionine residue in position 35 with norleucine, a mutation that abolishes the ability of A beta to produce free radicals, abolished its vascular effects. Nanomolar concentrations of A beta 1-40 constricted isolated pressurized middle cerebral artery segments with intrinsic tone (-16 +/- 3% at 100 nM; P < 0.05). We conclude that A beta acts directly on cerebral arteries to produce vasoconstriction and to enhance selected constrictor responses. The evidence supports the idea that A beta-induced production of reactive oxygen species plays a role in this effect. The vascular actions of A beta may contribute to the deleterious effects resulting from accumulation of this peptide in Alzheimer's dementia.

VAPSE-based analysis: a two-phased candidate gene approach for elucidating genetic predisposition to complex disorders

The extraordinary success of linkage analysis in diseases with Mendelian inheritance has not extended readily to the genetics of common complex diseases. VAPSE-based analysis is a type of candidate gene approach that represents an alternative strategy by which genetic mechanisms can be defined despite the presence of substantial genetic heterogeneity. Recent advances in mutation screening and statistical methodology have enhanced substantially the efficiency and power of this approach. The "bread and butter" of VAPSE-based analysis is genotype-to-phenotype searches in large populations with computerized medical records.

The load and distribution of beta-amyloid in brain tissue of patients with Alzheimer's disease

Recent findings have underlined the significance of beta-amyloid protein (betaA4) in the etiology of Alzheimer's disease (AD). In 60 patients with AD, the amount of betaA4 deposition, estimated applying immunohistochemical techniques, was shown to be significantly influenced by apolipoprotein E (ApoE) genotype (epsilon4/epsilon4 > epsilon4/x > x/x), by the age at onset (presenile > senile), by the age at death (younger > older patients) and by the duration of the disease (long > short). Morphometric analysis revealed that the betaA4 load was highest in the superficial layer of the cortex and a significant influence on the vertical distribution was seen in females but not in males, in familial but not in sporadic cases and in senile but not in presenile cases. Our findings indicate that not only the load but also the vertical distribution of betaA4 within cortex is influenced by risk factors such as ApoE genotype and gender.

Preventing dementia

Primary prevention will become increasingly important as dementia prevalence increases and effective retardive therapies are developed. To date, only one randomized controlled trial (involving treatment of systolic hypertension) has demonstrated that the incidence of dementia can be reduced. Physicians should remain alert to possible secondary causes of dementia and correct these whenever possible. Primary and secondary prevention of stroke should reduce dementia related to cerebrovascular disease either directly or as a comorbid factor in Alzheimer's disease (AD). Epidemiological studies have revealed a number of risk factors for AD including genetic mutation, susceptibility genes, positive family history, Down's syndrome, age, sex, years of education, head trauma and neurotoxins. In case-control studies non-steroidal anti-inflammatory medication and estrogen replacement therapy appear to decrease the relative risk of developing AD. Further research to develop and test preventative therapies in AD and other dementias should be strongly encouraged.

Exogenous A beta1-40 reproduces cerebrovascular alterations resulting from amyloid precursor protein overexpression in mice

Transgenic mice overexpressing the amyloid precursor protein (APP) have a profound impairment in endothelium-dependent cerebrovascular responses that is counteracted by the superoxide scavenger superoxide dismutase (SOD). The authors investigated whether the amyloid-beta peptide (A beta) is responsible for the cerebrovascular effects of APP overexpression. Cerebral blood flow (CBF) was monitored by a laser-Doppler flowmeter in anesthetized-ventilated mice equipped with a cranial window. Superfusion of A beta1-40 on the neocortex reduced resting CBF in a dose-dependent fashion (-29% +/- 7% at 5 micromol/L) and attenuated the increase in CBF produced by the endothelium-dependent vasodilators acetylcholine (-41% +/- 8%), bradykinin (-39% +/- 9%), and the calcium ionophore A23187 (-37% +/- 5%). A beta1-40 did not influence the CBF increases produced by the endothelium-independent vasodilators S-nitroso-N-acetylpenicillamine and hypercapnia. In contrast, A beta1-42 did not attenuate resting CBF or the CBF increases produced by endothelium-dependent vasodilators. Cerebrovascular effects of A beta1-40 were reversed by the superoxide scavengers SOD or MnTBAP. Furthermore, substitution of methionine 35 with norleucine, a mutation that blocks the ability of A beta to generate reactive oxygen species, abolished A beta1-40 vasoactivity. The authors conclude that A beta1-40, but not A beta1-42, reproduces the cerebrovascular alterations observed in APP transgenics. Thus, A beta1-40 could play a role in the cerebrovascular alterations observed in Alzheimer's dementia.

Abeta 1-40-related reduction in functional hyperemia in mouse neocortex during somatosensory activation

Peptides derived from proteolytic processing of the beta-amyloid precursor protein (APP), including the amyloid-beta peptide (Abeta), play a critical role in the pathogenesis of Alzheimer's dementia. We report that transgenic mice overexpressing APP and Abeta have a profound attenuation in the increase in neocortical blood flow elicited by somatosensory activation. The impairment is highly correlated with brain Abeta concentration and is reproduced in normal mice by topical neocortical application of exogenous Abeta1-40 but not Abeta1-42. Overexpression of M146L mutant presenilin-1 in APP mice enhances the production of Abeta1-42 severalfold, but it does not produce a commensurate attenuation of the hyperemic response. APP and Abeta overexpression do not diminish the intensity of neural activation, as reflected by the increase in somatosensory cortex glucose usage. Thus, Abeta-induced alterations in functional hyperemia produce a potentially deleterious mismatch between substrate delivery and energy demands imposed by neural activity.

Apolipoprotein E includes a binding site which is recognized by several amyloidogenic polypeptides

Inheritance of the apolipoprotein E (apoE) epsilon 4 allele is a risk factor for late-onset Alzheimer's disease (AD). Biochemically apoE is present in AD plaques and neurofibrillary tangles of the AD brain. There is a high avidity and specific binding of apoE and the amyloid beta-peptide (A beta). In addition to AD apoE is also present in many other cerebral and systemic amyloidoses, Down's syndrome and prion diseases but the pathophysiological basis for its presence is still unknown. In the present study we have compared the interaction of apoE with A beta, the gelsolin-derived amyloid fragment AGel(183-210) and the amyloidogenic prion fragments PrP(109-122) and PrP(109-141). We show that, similar to A beta, also AGel and PrP fragments can form a complex with apoE, and that the interaction between apoE and the amyloidogenic protein fragments is mediated through the same binding site on apoE. We also show that apoE increases the thioflavin-T fluorescence of PrP and AGel and that apoE influences the content of beta-sheet conformation of these amyloidogenic fragments. Our results indicate that amyloids and amyloidogenic prion fragments share a similar structural motif, which is recognized by apoE, possibly through a single binding site, and that this motif is also responsible for the amyloidogenicity of these fragments.

A genealogical study of Alzheimer disease in the Saguenay region of Quebec

We performed an analysis of inbreeding and kinship among the ascending genealogies of 205 autopsy-confirmed Alzheimer disease (AD) subjects recruited in the Saguenay area of Québec. We hypothesized that if some traits pertaining to the disease were determined by inherited factors, and if the corresponding genes were not too frequent in the population, it might be possible to detect some clusters of patients related to common ancestors and presenting a level of kinship and/or inbreeding higher than is observed in the unaffected population of the same age. In view of the heterogeneity of the disease, we also verified if some of the factors investigated could be associated more specifically with subsets of cases based on age of onset and on apolipoprotein E (APOE) genotype. Results were compared with those obtained on 205 controls matched for gender, place and year of birth. We found that late-onset AD cases with an APOE-epsilon 4 were significantly more inbred than controls and that this increase was explained by the high level of inbreeding of a few cases whose parents were related at the first-cousin level. This could possibly indicate the implication of a recessive element in a small subset of AD cases in the Saguenay population. We also found that late-onset epsilon 4+ cases were significantly more closely related among themselves than with controls. This increase in kinship may be attributable to the presence of the epsilon 4 allele or to some other unidentified genetic factor possibly acting in conjunction with APOE-epsilon 4.

Risk for Alzheimer's disease in older late-onset cases is associated with HLA-DRB1*03

The allele frequency of the HLA-DRB1 gene was compared between groups of 48 clinically diagnosed elderly Alzheimer's disease (AD) cases and 44 pathologically confirmed elderly control cases. Specific primers were used to PCR amplify the highly polymorphic second exon of HLA-DRB1 using DNA extracted from blood samples or frozen brain tissue. The allele type was identified using sequence specific oligonucleotide probes. The results showed an increased frequency of DRB1*03 (P < 0.006) and decreased frequency of DRB1*09 (P < 0.049) in the AD cases compared with the controls. The results suggest that DRB1*03 is associated with an increased risk and DRB1*09 a possible decreased risk for the development of late-onset AD with first detectable clinical symptoms occurring at age 75 years or greater.

Alpha-2-macroglobulin intronic polymorphism is not associated with autopsy-confirmed late-onset Alzheimer's disease

Alpha-2-macroglobulin (A2M) intronic polymorphism has recently been reported to be associated with late-onset Alzheimer's disease (LOAD). To corroborate this association, we analysed the A2M and apolipoprotein E (APOE) polymorphisms in autopsy cases of the MRC Alzheimer's Disease Brain Bank, Institute of Psychiatry, London. The frequencies of the insertion and deletion alleles in AD were 0.81 and 0.19, respectively, and these were not significantly different from control frequencies. After pooling the AD cases in epsilon4 positive and negative subgroups, there was again no significant difference between the A2M allele frequency in the two subgroups. In our present study, we were unable to corroborate the association between A2M intronic polymorphism and LOAD in autopsy cases.

The genetics of Alzheimer disease and the application of molecular tests

Two general classes of genes are associated with the development of Alzheimer disease (AD). The first group consists of genes that appear to cause AD when mutated, and the second category is composed of genes that are statistically associated with AD, depending on the inheritance of specific alleles. This paper reviews the current state of knowledge about the genetics of AD, and we then discuss the two molecular tests that are currently commercially available. These include a genetic test for mutations in the presenilin 1 (PS1) gene that can diagnose or predict a subset of early onset familial AD with a high degree of certainty. The value of the genetic test for the apolipoprotein (APOE) allele status is far less clear. Inheritance of the epsilon 4 allele is associated with an increased risk of AD at a population level, but APOE genotyping is inappropriate for prediction of future disease in an individual and offers only a marginal increase in diagnostic certainty when symptomatic individuals are tested. In the future, genetic tests may become more broadly applicable to the diagnosis and prediction of AD. However, the utility of such tests is currently limited to a small subset of individuals because in the vast majority of AD cases no clear genetic or environmental cause has been defined.

Genetic evidence for oxidative stress in Alzheimer's disease

The cause and proximal consequences of Alzheimer's disease (AD), a progressive debilitating dementia remain largely unknown. Nonetheless an increasing number of genetic risk factors, including most recently bleomycin hydrolase, have been shown to be associated with the disease, offering the hope of revealing the mechanism of disease pathogenesis. Here we show that bleomycin hydrolase, known to be induced in an oxidative environment, is specifically increased in neurons marked for degeneration in AD. These findings support a key proximal role for bleomycin hydrolase, and oxidative stress in AD.

Frequency of HLA-A and B alleles in early and late-onset Alzheimer's disease

The frequency of various allele types of the class I Major Histocompatibility Complex (MHC) genes HLA-A and HLA-B were compared between pathologically confirmed groups of late and early-onset Alzheimer's disease (AD) and a control group. DNA was extracted from frozen brain tissue and the highly polymorphic second and third exons of the HLA-A and HLA-B genes were independently PCR amplified using specific primers. Individual allele types were identified using sequence-specific oligonucleotide probes. The results showed that the main frequency differences occurred between the late-onset AD and the control group however none of these reached statistical significance.

Recent advances in the genetics of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is the most common cause of dementia in the elderly. It is a clinical-pathologic entity characterized by progressive dementia associated with the neuropathologic hallmarks of Abeta amyloid plaques, neurofibrillary tangles (NFTs), neuronal loss, and amyloid angiopathy. Three "causative" AD genes (i.e., genes in which a mutation is sufficient to result in clinical AD) for early-onset familial Alzheimer's disease (FAD) and one "susceptibility" gene that affects risk and age of onset of AD in familial and sporadic late-onset AD have been identified. The three causative genes are the amyloid precursor protein (APP gene) on chromosome 21, the presenilin-1 gene on chromosome 14, and the presenilin-2 gene on chromosome 1. The susceptibility gene is the apolipoprotein E (APOE) gene on chromosome 19. Investigations of the normal and aberrant function of these genes will provide insights into the mechanisms underlying AD and will suggest new strategies for therapeutic intervention.

An evaluation of the role of mitochondria in neurodegenerative diseases: mitochondrial mutations and oxidative pathology, protective nuclear responses, and cell death in neurodegeneration

There is mounting evidence for mitochondrial involvement in neurodegenerative diseases including Alzheimer's and Parkinson's disease and amyotrophic lateral sclerosis. Mitochondrial DNA mutations, whether inherited or acquired, lead to impaired electron transport chain (ETC) functioning. Impaired electron transport, in turn, leads to decreased ATP production, formation of damaging free-radicals, and altered calcium handling. These toxic consequences of ETC dysfunction lead to further mitochondrial damage including oxidation of mitochondrial DNA, proteins, and lipids, and opening of the mitochondrial permeability transition pore, an event linked to cell death in numerous model systems. Although protective nuclear responses such as antioxidant enzymes and bcl-2 may be induced to combat these pathological changes, such a vicious cycle of increasing oxidative damage may insidiously damage neurons over a period of years, eventually leading to neuronal cell death. This hypothesis, a synthesis of the mitochondrial mutations and oxidative stress hypotheses of neurodegeneration, is readily tested experimentally, and clearly points out many potential therapeutic targets for preventing or ameliorating these diseases.

Aggravated decrease in the activity of nucleus basalis neurons in Alzheimer's disease is apolipoprotein E-type dependent

As reported before, the metabolic activity of nucleus basalis neurons is reduced significantly in Alzheimer patients. Because the apolipoprotein E (ApoE) epsilon4 genotype is a major risk factor for Alzheimer's disease (AD), we determined whether the decrease in metabolic activity in nucleus basalis neurons in AD is ApoE-type dependent. The size of the Golgi apparatus (GA) was determined as a measure of neuronal metabolic activity in 30 controls and 41 AD patients with a known ApoE genotype by using an image analysis system in the nucleus basalis of Meynert. A polyclonal antibody directed against MG-160, a sialoglycoprotein of the GA, was used to visualize this organelle. There was a very strong reduction in the size of the GA in the nucleus basalis of AD patients. Furthermore, a strong and significant extra reduction in the size of the GA was found in the nucleus basalis neurons of AD patients with either one or two ApoE epsilon4 alleles compared with Alzheimer patients without ApoE epsilon4 alleles. Our data show that the decreased activity of nucleus basalis neurons in AD is ApoE epsilon4 dependent and suggest that ApoE epsilon4 participates in the pathogenesis of AD by decreasing neuronal metabolism.

Cyclosporin A increases resting mitochondrial membrane potential in SY5Y cells and reverses the depressed mitochondrial membrane potential of Alzheimer's disease cybrids

Alzheimer's disease (AD) brains exhibit oxidative stress and a biochemical defect of complex IV (cytochrome oxidase, COX) of the mitochondrial electron transport chain (ETC). This defect can be transferred through mitochondrial DNA (mtDNA) into clonal SY5Y cells depleted of their mtDNA. The resulting cytoplasmic hybrids or "cybrids" retain the complex IV defect and exhibit oxidative stress. We measured the mitochondrial membrane potential (delta psi m) in AD and control cybrids via H3-tetraphenylphosphonium ion (H3-TPP+) accumulation. AD cybrids exhibited a significant (about 30%) decrease in H3-TPP+ accumulation relative to controls. Acute treatment of normal SY5Ys with azide, a COX inhibitor, moderately decreased H3-TPP+ retention and strongly inhibited COX activity in a dose-dependent manner. As the mitochondrial transition pore (MTP) can be activated by reactive oxygen species and ETC inhibitors, and its opening causes delta psi m dissipation, we tested the effects of the MTP inhibitor cyclosporin A (CsA) on TPP+ accumulation. 5mM CsA increased basal H3-TPP+ accumulation in SY5Y cells about 10-fold, corresponding to about a 2-fold increase in delta psi m. In the AD cybrids, CsA increased the apparent delta psi m to the same final levels as it did in controls. These results indicate that low-conductance MTP activity contributes significantly to resting delta psi m in SY5Y cells. We propose the novel hypothesis that the COX defect and resulting oxidative stress in AD may pathologically activate the MTP, resulting in lower delta psi m and the release of mitochondrial factors involved in apoptosis.

Copper, iron and zinc in Alzheimer's disease senile plaques

Concentrations of copper (Cu), iron (Fe) and zinc (Zn) were measured in the rims and cores of senile plaques (SP) and in the neuropil of the amygdala of nine Alzheimer's disease (AD) patients and in the neuropil of the amygdala of five neurologically normal control subjects using micro particle-induced X-ray emission (micro-PIXE). Comparison of SP rim and core values revealed no significant differences between levels of Cu, Fe or Zn. Zinc and Fe in SP rims and cores were significantly elevated in AD compared with AD neuropil (P<0.05). Copper was significantly elevated (P<0.05) in the rim of SP compared with AD neuropil. Comparison of AD and control neuropil revealed a significant (P<0.05) elevation of Zn in AD subjects. The elevation of these elements in SP in AD is of interest in light of the observation that Cu, Fe and particularly Zn, can accelerate aggregation of amyloid beta peptide.

Alzheimer's disease and brain development: common molecular pathways

Research on the causes and treatments of Alzheimer's disease (AD) has led investigators down numerous avenues. Although many models have been proposed, no single model of AD satisfactorily accounts for all neuropathologic findings as well as the requirement of aging for disease onset. The mechanisms of disease progression are equally unclear. We hypothesize that alternative gene expression during AD plays a critical role in disease progression. Numerous developmentally regulated genes and cell cycle proteins have been shown to be re-expressed or activated during AD. These proteins include transcription factors, members of the cell cycle regulatory machinery, and programmed cell death genes. Such proteins play an important role during brain development and would likely exert powerful effects if re-expressed in the adult brain. We propose that the re-expression or activation of developmentally regulated genes define molecular mechanisms active both during brain development and in AD.

Apparent mtDNA heteroplasmy in Alzheimer's disease patients and in normals due to PCR amplification of nucleus-embedded mtDNA pseudogenes

In an unprecedented finding, Davis et al. [Davis, R. E., Miller, S., Herrnstadt, C., Ghosh, S. S., Fahy, E., Shinobu, L. A., Galasko, D., Thal, L. J., Beal, M. F., Howell, N. & Parker, W. D., Jr. (1997) Proc. Natl. Acad. Sci. USA 94, 4526-4531] used an unusual DNA isolation method to show that healthy adults harbor a specific population of mutated mitochondrial cytochrome c oxidase (COX) genes that coexist with normal mtDNAs. They reported that this heteroplasmic population was present at a level of 10-15% in the blood of normal individuals and at a significantly higher level (20-30%) in patients with sporadic Alzheimer's disease. We provide compelling evidence that the DNA isolation method employed resulted in the coamplification of authentic mtDNA-encoded COX genes together with highly similar COX-like sequences embedded in nuclear DNA ("mtDNA pseudogenes"). We conclude that the observed heteroplasmy is an artifact.