Association of the apolipoprotein E epsilon 4 allele with clinical subtypes of autopsy-confirmed Alzheimer's disease

Amyloid β-Peptide Effects on Glucose Regulation Are Dependent on Apolipoprotein E Genotype

The apolipoprotein E gene (APOE) confers the greatest genetic risk factor for Alzheimer's disease (AD), wherein the ε4 allele confers an elevated risk compared with the ε3 allele. Biological mechanisms that differ across these alleles have been explored in mouse models wherein the murine Apoe gene has undergone targeted replacement with sequences encoding human ApoE3 or ApoE4 (ApoE-TR mice). Such models have indicated that the two variants of ApoE produce differential effects on energy metabolism, including metabolic syndrome. However, glucose regulation has not been compared in ApoE-TR mice with and without amyloid β-peptide (Aβ) accumulation. We crossed ApoE3-TR and ApoE4-TR mice with a transgenic line that accumulates human Aβ1-42 In male ApoE3-TR mice, introduction of Aβ caused aberrations in glucose tolerance and in membrane translocation of astrocytic glucose transporter 1 (GLUT1). Phosphorylation of Tau at AD-relevant sites was correlated with glucose intolerance. These effects appeared independent of insulin dysregulation and were not observed in females. In ApoE4-TR mice, the addition of Aβ had no significant effects because of a trend toward perturbation of the baseline values.

"Choosing Wisely": Apolipoprotein E Genetic Testing for the Diagnosis of Alzheimer's Disease in Dementia Clinics

BACKGROUND

Apolipoprotein E (APOE) ɛ4 allele carriers have an increased risk of late-onset Alzheimer's disease (AD). However, in the "Choosing Wisely" campaign for avoiding unnecessary medical tests, treatments, and procedures, APOE genetic testing is not recommended as a predictive test for AD.

OBJECTIVE

The aim of this study was to investigate the potential value of APOE genetic testing in a specific clinical context.

METHODS

Subjects with poor performance in the Korean version of the Mini-Mental Status Examination for dementia screening (MMSE-DS) with a Z-score of less than -1.5 were recruited from the public health centers. All participants underwent APOE genetic testing. Family history of dementia (FHx) was confirmed if one or more first-degree relatives had dementia.

RESULTS

Among 349 subjects, 162 (46.4%) were diagnosed with AD. APOEɛ4 allele carriers had a much higher risk of AD in the group with FHx than in the group without FHx (OR = 15.81, 95% CI = 2.74-91.21 versus OR = 1.82, 95% CI = 1.00-3.27, z = 2.293, p = 0.011). The sensitivity, specificity, positive predictive value, and negative predictive value for the APOEɛ4 allele were 47.7%, 90.9%, 91.3%, and 46.5% in the group with FHx.

CONCLUSION

It would be a wise choice to perform the APOE genetic testing for the diagnosis of AD in subjects with poor performance in a screening test and a family history of dementia.

Genomic variants, genes, and pathways of Alzheimer's disease: An overview

Alzheimer's disease (AD) (MIM: 104300) is a highly heritable disease with great complexity in its genetic contributors, and represents the most common form of dementia. With the gradual aging of the world's population, leading to increased prevalence of AD, and the substantial cost of care for those afflicted, identifying the genetic causes of disease represents a critical effort in identifying therapeutic targets. Here we provide a comprehensive review of genomic studies of AD, from the earliest linkage studies identifying monogenic contributors to early-onset forms of AD to the genome-wide and rare variant association studies of recent years that are being used to characterize the mosaic of genetic contributors to late-onset AD (LOAD), and which have identified approximately ∼20 genes with common variants contributing to LOAD risk. In addition, we explore studies employing alternative approaches to identify genetic contributors to AD, including studies of AD-related phenotypes and multi-variant association studies such as pathway analyses. Finally, we introduce studies of next-generation sequencing, which have recently helped identify multiple low-frequency and rare variant contributors to AD, and discuss on-going efforts with next-generation sequencing studies to develop statistically well- powered and comprehensive genomic studies of AD. Through this review, we help uncover the many insights the genetics of AD have provided into the pathways and pathophysiology of AD. © 2016 Wiley Periodicals, Inc.

Apolipoprotein E allelotype is associated with neuropathological findings in Alzheimer's disease

In a consecutive hospital-based autopsy series, we examined the relationship between apolipoprotein E (apoE) and Alzheimer's disease (AD) and investigated the clinicopathological relationship in AD. The study population included 99 patients (mean age 81 years) with AD-related neuropathological findings at death, of whom 83 were diagnosed with AD according to the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) classification, and a control group of patients without neurodegenerative disease (n = 1429). The patients were apoE genotyped and the density of β-amyloid senile plaques, neuritic plaques and neurofibrillary tangles was estimated in the cortex and hippocampus. The utility of immunohistochemical staining using an antibody directed against apoE4 in paraffin-embedded tissue was also evaluated. Among patients with "definite AD" according to CERAD, 65 % were ε4 carriers, compared to 32 % among controls (p < 0.001). The risk of ε4 carriers to develop AD was higher (odds ratio = 4.65, p = 0.001) than for non-ε4 carriers. The amount of β-amyloid deposition and neurofibrillary pathology differed significantly (p < 0.01) between the genotypes, with increasing densities from ε2 carriers to homozygous ε4 carriers. The effect of ε4 on the presence of clinical symptoms was attenuated and non-significant after adjusting for AD-related neuropathological findings. There was an association between these findings and the presence of clinical symptoms of AD, with neurofibrillary tangles separating patients with and without symptoms of AD markedly better than β-amyloid. In addition, we found a strong relationship between genotype and immunohistochemical apoE4-staining intensity. In conclusion, this Scandinavian autopsy study shows that the apoE polymorphism is associated with the probability of AD and influences the deposition of β-amyloid and neurofibrillary pathology. Our findings suggest that the association between apoE and clinical manifestations of AD is mediated mainly through the neuropathological features of AD. Further, we found a relationship between AD-related findings and clinical symptoms of AD with neurofibrillary tangles associating most strongly with clinical symptoms. Finally, immunohistochemical staining in brain specimens is useful for determining ε4- or non-ε4-carrier status.

At the interface of sensory and motor dysfunctions and Alzheimer's disease

Recent evidence indicates that sensory and motor changes may precede the cognitive symptoms of Alzheimer's disease (AD) by several years and may signify increased risk of developing AD. Traditionally, sensory and motor dysfunctions in aging and AD have been studied separately. To ascertain the evidence supporting the relationship between age-related changes in sensory and motor systems and the development of AD and to facilitate communication between several disciplines, the National Institute on Aging held an exploratory workshop titled "Sensory and Motor Dysfunctions in Aging and AD." The scientific sessions of the workshop focused on age-related and neuropathologic changes in the olfactory, visual, auditory, and motor systems, followed by extensive discussion and hypothesis generation related to the possible links among sensory, cognitive, and motor domains in aging and AD. Based on the data presented and discussed at this workshop, it is clear that sensory and motor regions of the central nervous system are affected by AD pathology and that interventions targeting amelioration of sensory-motor deficits in AD may enhance patient function as AD progresses.

D10S1423 identifies a susceptibility locus for Alzheimer's disease (AD7) in a prospective, longitudinal, double-blind study of asymptomatic individuals: results at 14 years

Typical forms of Alzheimer's disease (AD) appear to be influenced by multiple susceptibility loci. This report describes the prospective, longitudinal, double-blind assessment of the age-specific risk of AD encountered by 325 asymptomatic first-degree relatives of AD probands who carried the D10S1423 (AD7) 234 bp allele, the APOE E4 allele, or both, after 14 years of systematic follow-up. A total of 30 incident cases of AD were detected during the first 3752 subject-years of surveillance. The effects of carrying either or both of the D10S1423 234 bp and APOE E4 alleles on the age-specific risk of developing AD were determined using Kaplan-Meier survival analysis. The risk of developing AD was the greatest for individuals who carried both alleles (Mantel-Cox statistic = 16.46, df = 3, P = 0.0009; Breslow statistic = 13.38, df = 3, P = 0.004). Cox proportional hazards models were developed to estimate the risk ratios for each genotype, controlling for the potential effects of age at recruitment, sex, and years of education. Only individuals who carried both risk alleles exhibited a risk ratio that differed significantly from 1 (risk ratio = 7.5, P = 0.002, 95% CI = 2.1-27.0). Neither age at recruitment, sex, nor years of education made significant contributions to the model, although women tended to be at greater risk (P = 0.06). Recent evidence that D10S1423 resides within open reading frame C10orf112, whose predicted product resembles a low-density lipoprotein receptor, suggests a molecular mechanism for this gene-gene interaction.

Parenchymal and vascular Abeta-deposition and its effects on the degeneration of neurons and cognition in Alzheimer's disease

The deposition of the amyloid beta-protein (Abeta) is one of the pathological hallmarks of Alzheimer's disease (AD). Abeta-deposits show the morphology of senile plaques and cerebral amyloid angiopathy (CAA). Senile plaques and vascular Abeta-deposits occur first in neocorti-cal areas. Then, they expand hierarchically into further brain regions. The distribution of Abeta plaques throughout the entire brain, thereby correlates with the clinical status of the patients. Imaging techniques for Abeta make use of the hierarchical distribution of Abeta to distinguish AD patients from non-AD patients. However, pathology seen in AD patients represents a late stage of a pathological process starting 10-30 years earlier in cognitively normal individuals. In addition to the fibrillar amyloid of senile plaques, oligomeric and monomeric Abeta is found in the brain. Recent studies revealed that oligomeric Abeta is presumably the most toxic Abeta-aggregate, which interacts with glutamatergic synapses. In doing so, dendrites are presumed to be the primary target for Abeta-toxicity. In addition, vascular Abeta-deposits can lead to capillary occlusion and blood flow disturbances presumably contributing to the alteration of neurons in addition to the direct neurotoxic effects of Abeta. All these findings point to an important role of Abeta and its aggregates in the neurodegenerative process of AD. Since there is already significant neuron loss in AD patients, treatment strategies aimed at reducing the amyloid load will presumably not cure the symptoms of dementia but they may stop disease progression. Therefore, it seems to be necessary to protect the brain from Abeta-toxicity already in stages of the disease with minor neuron loss before the onset of cognitive symptoms.

Cognitive phenotypes in Alzheimer's disease and genetic risk

Variation in the clinical characteristics of patients with Alzheimer's disease (AD) is increasingly recognised, although the factors underlying variation are not fully understood. The study examined the cognitive characteristics of 523 AD patients at the time of their presentation to a neurological dementia clinic and explored the relationship to family history and apolipoprotein E (APOE) genotype. Distinct profiles were identified, which were mirrored by topographical differences on neuroimaging. Clinical distinctions were maintained over time. Two-thirds of patients showed a constellation of deficits at presentation which included memory, language, visuospatial and constructional difficulties. However, a quarter had circumscribed presentations of amnesia, aphasia, perceptuospatial disorder or apraxia. The rare presence of frontal lobe characteristics was associated with a younger age of onset, an increased incidence of myoclonus at presentation, a positive family history but not with possession of APOE epsilon4 allele. An amnestic presentation (severe, yet circumscribed amnesia) was strongly associated with an older age of onset, a positive family history and the presence of APOE epsilon4 allele. Posterior cortical presentations showed a female bias, were typically sporadic, and showed no association with APOE epsilon4. The findings support the notion of phenotypic variation in AD, and show that genetic risk factors can influence clinical presentation. The findings draw attention to the specific association between APOE epsilon4 allele and memory but challenge the commonly held notion that the presence of the epsilon4 allele inevitably reduces onset age. The findings indicate that risk factors other than APOE epsilon4 allele underlie the non-familial, early onset posterior hemisphere presentations of AD.

Cladistic approaches to identifying determinants of variability in multifactorial phenotypes and the evolutionary significance of variation in the human genome

Genetic surveys based on detailed restriction site mapping or DNA sequencing allow one to identify many different classes of mutational change at the molecular level and to estimate the evolutionary history of the genetic variation (a haplotype tree). These two sources of information can be combined in a powerful fashion to test hypotheses about the evolutionary significance of genetic variation and to identify mutations that are associated with diseases. Hypotheses about selection on various classes of genetic variation can be tested by examining the distribution patterns of different mutational classes upon the haplotype tree. The power of this procedure can be enhanced if it is coupled with comparative data from other, closely related species. With respect to disease associations, all mutations that affect phenotypic variation in a population occurred at some point in the evolutionary history of the region of the gene containing the mutations. Even if this evolutionary history is estimated from mutations other than those causing phenotypic effects, the phenotypically important mutations are imbedded in this same evolutionary history. Hence, whole branches (clades) of the haplotype tree should display homogeneous phenotypic effects and this fact is utilized to search for phenotypic associations of haplotypes by using nested clades in a haplotype tree. This procedure has more power than alternatives that do not use evolutionary history, and it avoids several statistical and interpretative problems associated with single-marker analyses. All of these methods could be used more extensively if more human genetic surveys concentrated on greater genetic resolution in small DNA regions and included non-human apes.

Cumulative lead dose and cognitive function in adults: a review of studies that measured both blood lead and bone lead

OBJECTIVE

We review empirical evidence for the relations of recent and cumulative lead dose with cognitive function in adults.

DATA SOURCES

A systematic search of electronic databases resulted in 21 environmental and occupational studies from 1996 to 2006 that examined and compared associations of recent (in blood) and cumulative (in bone) lead doses with neurobehavioral outcomes.

DATA EXTRACTION

Data were abstracted after consideration of exclusion criteria and quality assessment, and then compiled into summary tables.

CONCLUSIONS

At exposure levels encountered after environmental exposure, associations with bio-markers of cumulative dose (mainly lead in tibia) were stronger and more consistent than associations with blood lead levels. Similarly, in studies of former workers with past occupational lead exposure, associations were also stronger and more consistent with cumulative dose than with recent dose (in blood). In contrast, studies of currently exposed workers generally found associations that were more apparent with blood lead levels; we speculate that the acute effects of high, recent dose may mask the chronic effects of cumulative dose. There is moderate evidence for an association between psychiatric symptoms and lead dose but only at high levels of current occupational lead exposure or with cumulative dose in environmentally exposed adults.

Myocyte enhancing factor-2A in Alzheimer's disease: Genetic analysis and association with MEF2A-polymorphisms

Polymorphisms at different genes have been proposed as determinants of the risk for developing late-onset Alzheimer's disease (LOAD). Among the several candidate genes are those that encode proteins involved in neuronal degeneration/survival. Studies of primary neuronal cultures supported that members of the myocyte enhancing factor-2 (MEF2) family of transcription factors have an anti-apoptotic effect, regulating the expression of proteins involved in neuronal survival and differentiation. We analysed the MEF2A gene in a total of 357 patients (mean age 72 years, range 60-97 years). Among others, a Pro279Leu in exon 8 and a polyglutamine (CAG) repeat polymorphisms in exon 12 were found. These variants were also genotyped in 495 healthy controls (>50 years old), and the frequencies were statistically compared. Eight patients were 279L (six P/L and two L/L), compared to only one control (2% vs. 0.2%; p=0.004, OR=11.32). There was a significantly higher frequency of 279L-carriers among APOE epsilon4+ (7/154=4.5%), compared to epsilon4- (1/203) (p=0.02). In conclusion, our work suggests that the variation at the MEF2A gene could be involved in the risk of developing LOAD. Because MEF2 has been related with neuronal survival, and the 279L allele has been related with a reduction in the transcriptional activation activity of MEF2A, the effect of this allele could be mediated through a down-regulation of antiapoptotic genes.

Microglial activation in Alzheimer disease: Association with APOE genotype

Microglial cells are considered to play an important role in the pathogenesis of Alzheimer disease. Apart from producing the Alzheimer amyloid precursor (APP) as an acute phase protein, microglial cells seem to be involved in the deposition of its amyloidogenic cleavage product, the amyloid-beta peptide (Abeta). Abeta is bound by apolipoprotein E (APOE) in an isoform-specific manner, and it has been demonstrated that inheritance of the AD susceptibility allele, APOE epsilon4, is associated with increased deposition of Abeta in the cerebral cortex. However, the relationship between APOE epsilon4 gene dose and microglial activation is unknown. Using microglial expression of major histocompatibility complex class II molecules as a marker, we have performed a quantitative genotype-phenotype analysis on microglial activation in frontal and temporal cortices of 20 APOE genotyped AD brains. The number of activated microglia and the tissue area occupied by these cells increased significantly with APOE epsilon4 gene dose. When a model of multiple linear regression was used to compare the relative influence of APOE genotype, sex, disease duration, age at death, diffuse and neuritic plaques as well as neurofibrillary tangles on microglial activation, only APOE genotype was found to have a significant effect. Thus, the APOE gene product represents an important determinant of microglial activity in AD. Since microglial activation by APP has been shown to be modulated by apoE in vitro, a direct role of microglia in AD pathogenesis is conceivable.

Aberrant accentuation of neurofibrillary degeneration in the hippocampus of Alzheimer's disease with amyloid precursor protein 717 and presenilin-1 gene mutations

This study reports correlation of the hippocampal neurofibrillary tangles (NFT) density with beta-amyloid (Abeta) precursor protein (APP) 717 mutation, presenilin (PS)-1 mutation and apolipoprotein E (Apo-E) e4 alleles (E4), being graded as 3 forms (no-E4, one-E4 and two-E4) in autopsied brains from patients with familial and non-familial Alzheimer's disease (AD). We studied the density of NFT-free neurons, intracellular NFT (I-NFT), extracellular NFT (E-NFT) and total NFT (I-NFT plus E-NFT) in the six hippocampal subdivisions: cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. The APP mutation cases showed significantly higher total NFT density in the CA1-CA2 region, and the PS-1 mutation cases also showed higher density of total NFT in the CA1-CA3 than non-familial cases. Moreover, high densities of the E-NFT contributed to these high total NFT densities. Non-familial AD cases showed a stereotypical NFT distribution with entorhinal accentuation in the hippocampus irrespective of E4 frequency. Thus, APP and PS-1 mutations predominantly affect the CA regions with profound neurodegeneration, which contributes early and severe clinical features of familial AD.

Relationship of neurofibrillary pathology to cerebral amyloid angiopathy in Alzheimer's disease

Over 90% of patients with Alzheimer's disease (AD) develop cerebral amyloid angiopathy (CAA). Severe dyshoric CAA, in which amyloid extends into the surrounding brain parenchyma, may be associated with adjacent clustering of tau-immunopositive neurites but the relationship of CAA to neurofibrillary pathology has not been systematically investigated. In the present study this relationship was examined in sections of frontal, temporal and parietal cortex from 25 AD patients with moderate to severe CAA and 26 with mild or absent CAA. We measured immunolabelling of abnormally phosphorylated tau adjacent to A beta-laden and non-A beta-laden arteries and arterioles, and in cortex away from arteries and arterioles. We also analysed the possible influence of APOE genotype on these measurements. There were no significant differences between the lobes in measurements of tau labelling, either around blood vessels or elsewhere in the cortex. However, tau labelling around A beta-laden arteries and arterioles significantly exceeded that around non-A beta-laden blood vessels (P<0.001) and this, in turn was greater than the labelling of cortex away from blood vessels (P<0.001). There was no association between APOE epsilon 4 and the immunolabelling density for tau, whether around amyloid- or non-amyloid-laden arteries and arterioles, or in the cerebral cortex away from these. We propose that both CAA and peri-vascular accumulation of hyperphosphorylated tau may be a consequence of elevated levels of soluble A beta around cortical arteries and arterioles.

Tau pathology in the olfactory bulb correlates with Braak stage, Lewy body pathology and apolipoprotein ɛ4

Olfactory dysfunction increases with disease severity in Alzheimer's disease (AD), is early and independent of disease severity in Parkinson's disease (PD), but is absent in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). Previous histopathologic studies of olfactory bulbs in AD have shown neurofibrillary tangles (NFTs) and senile plaques while Lewy bodies (LBs) have been described in PD. Little is known about olfactory bulb pathology in PSP and CBD. Tau and alpha-synuclein pathology was assessed with immunohistochemistry in olfactory bulbs of AD (N=15), Lewy body disease (LBD; N=10), LBD with concurrent AD (AD/LBD; N=19), PSP (N=27), CBD (N=3) and cases with no significant neurodegenerative pathology (NSP; N=15). The Braak NFT stage, counts of senile plaques and NFT in cortical and hippocampal sections, and counts of LBs in amygdala and cortical sections were recorded for each case. Apolipoprotein E (APOE) genotypes were determined on DNA prepared from frozen brain tissue. All AD and AD/LBD cases and nine of 10 LBD cases had tau pathology in the anterior olfactory nucleus (AON), but it was uncommon in PSP (9/27), CBD (0/3) and NSP (5/15). Multiple linear regression analysis demonstrated that tau pathology in the AON correlated with Braak stage (P<0.001), cortical LB counts (P<0.001), as well as APOE epsilon4. Tau pathology is common in the olfactory bulb of AD and LBD but is minimal or absent in PSP and CBD. It correlates with APOE epsilon4, severity of tau pathology in the brain and surprisingly with cortical and amygdala LBs, suggesting a possible synergistic effect between tau and synuclein in the AON in cases with both pathologic processes.

Expanding the association between the APOE gene and the risk of Alzheimer's disease: possible roles for APOE promoter polymorphisms and alterations in APOE transcription

Alzheimer's disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early-onset AD may be explained by single gene defects; however, most AD cases are late onset (> 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The epsilon4 allele of APOE is one of three (epsilon2 epsilon3 and epsilon4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the epsilon 4 allele is recognized as the most common identifiable genetic risk factor for late-onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOE epsilon4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the epsilon2/epsilon3/epsilon4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the epsilon2/epsilon3/epsilon4 locus.

Tau load is associated with apolipoprotein E genotype and the amount of amyloid beta protein, Abeta40, in sporadic and familial Alzheimer's disease

The total amount of hyperphosphorylated tau protein (p-tau load), present as neurofibrillary tangles (NFTs), neuropil threads or plaque neurites, was quantified in the frontal cortex of 109 cases of sporadic Alzheimer's disease (AD) and 35 cases of familial AD due to missense mutations in the presenilin-1, presenilin-2 and amyloid precursor protein genes. p-tau load was inversely correlated with age at onset of illness in both sporadic and familial AD but not with duration of disease. There was no difference in p-tau load between cases of familial AD and others with sporadic AD, matching the familial cases for apolipoprotein E (APO E) genotype. However, p-tau was greater in cases of familial and sporadic AD in the presence of APO E epsilon4 allele and increased with gene dose. Conversely, p-tau load tended to be lower when epsilon2 allele was present. In sporadic AD, tau load was highly significantly correlated with amyloid beta40 (Abeta40), but not Abeta42(43), load. These data indicate that the burden of pathological tau deposited in the brain in both familial and sporadic AD is favoured in the presence of APO E epsilon4 allele and also related to the amount of Abeta40, this also being higher when epsilon4 allele is present. Abeta40 plaques are rich in microglial cells and it is possible that p-tau pathology in AD is triggered by reaction of microglial cells to the presence of Abeta40 and not this peptide directly.

Genome survey for susceptibility loci for recurrent, early-onset major depression: results at 10cM resolution

Recurrent (two or more episodes), early-onset (first episode at < or = 25 years) major depressive disorder (RE-MDD) is a strongly familial condition (lambda(first-degree relatives) = 8) whose malignant effects have a significant negative impact on the health and longevity of patients and their family members. The goal of this study was to identify candidate susceptibility loci that influence the development of RE-MDD. We completed a systematic survey of the human genome, conducted at an average resolution of 10 cM, for the identification of simple sequence tandem repeat polymorphisms (SSTRPs) that target susceptibility genes for RE-MDD by virtue of linkage disequilibrium. The efficiency of our association study was enhanced by genotyping pools of DNA from 100 adults with RE-MDD and 100 adult controls who had no personal or family history of mental disorders. Both groups included equal numbers of Caucasian men and women and were matched as closely as possible for age and ethnicity. Allelic associations with RE-MDD were observed for 19 of the 387 SSTRPs in the CHLC Human Screening Set/Weber Version 9. Sixteen of the 19 candidate susceptibility loci revealed significant allelic associations with RE-MDD in men (n = 7) or women (n = 9), but not in both sexes. Evidence for both risk and protective alleles was detected. Two of the candidate susceptibility loci reside within several Mb of loci previously reported-megabases to be linked to "comorbid alcoholism and depression" in families of individuals with alcoholism and to a broadly defined affected phenotype that included recurrent major depression in the families of patients with bipolar disorder. Although it has been suggested that the genes that influence risk for MDD in the two sexes may not be entirely the same, the results of our study suggest that sex specificity of susceptibility loci for RE-MDD may be the rule rather than the exception. The observed preponderance of sex-specific susceptibility loci for RE-MDD suggests that there may be important differences in the molecular pathophysiology of RE-MDD in men and women. Alternatively, our findings may reflect the existence of sex-specific differences in the molecular mechanisms that determine resilience to endogenous or environmental depressogenic stimuli.

Using meta-analysis to explain the diversity of results in genetic studies of late-onset Alzheimer's disease and to identify high-risk subgroups

In late-onset Alzheimer's disease, there is a puzzling inconsistency between the findings of case-control studies of most proposed risk genes, except apolipoprotein E epsilon4. This inconsistency may stem from the failure to define the genetic and non-genetic interactions that affect the disease association of each particular susceptibility gene. Such interactions will limit the influence of the gene to a 'relevant subset' of vulnerable people. The relevant subsets for many risk genes will be narrow, compared to that of apolipoprotein E epsilon4. Studies may therefore miss the association or even suggest that a risk gene is protective. In these circumstances, the precise composition of a cohort is critical and defining the relevant subset is crucial. We illustrate how such definition may be achieved through meta-analysis. We take as an example the butyrylcholinesterase K variant, whose association with Alzheimer's disease may now be provisionally defined. This analysis leads to the identification of a potentially high-risk group: over 75 year old male carriers of both apolipoprotein E epsilon4 and butyrylcholinesterase K variant.

Two types of sporadic cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a type of beta-amyloidosis that occurs in leptomeningeal and cortical vessels of the elderly. In a sample of 41 CAA cases including 16 Alzheimer disease (AD) cases and 28 controls, we show that 2 types of sporadic CAA exist: The first type is characterized by immunohistochemically detectable amyloid beta-protein (Abeta) in cortical capillaries, leptomeningeal and cortical arteries, arterioles, veins, and venules. It is referred to here as CAA-Type 1. The second type of CAA also exhibits immunohistochemically detectable Abeta deposits in leptomeningeal and cortical vessels, with the exception of cortical capillaries. This type is termed CAA-Type 2. In cases with CAA-Type 1, the frequency of the apolipoprotein E (ApoE) epsilon4 allele is more than 4 times greater than in CAA-Type 2 cases and in controls. CAA-Type 2 cases have a higher epsilon2 allele frequency than CAA-Type 1 cases and controls. The ratio of CAA-Type 2 to CAA-Type 1 cases does not shift significantly with respect to the severity of AD-related beta-amyloidosis, with respect to degrees of CAA-severity, or with increasing age. Therefore, CAA-Type 1 is unlikely to be the late stage of CAA-Type 2; rather, they represent 2 different entities. Since both the ApoE epsilon2 and the epsilon4 allele are known to be risk factors for CAA, we can assign the risk factor ApoE epsilon4 to a distinct morphological type of CAA. The ApoE epsilon4 allele constitutes a risk factor for CAA-Type 1 and, as such, for neuropil-associated dyshoric vascular Abeta deposition in capillaries, whereas the e2 allele does not. CAA-Type 2 is not associated with the epsilon4 allele as a risk factor but shows a higher epsilon2 allele frequency than CAA-Type 1 cases and controls in our sample.

D10S1423 identifies a susceptibility locus for Alzheimer's disease in a prospective, longitudinal, double-blind study of asymptomatic individuals

Typical, later-onset forms of Alzheimer's disease (AD) appear to be influenced by multiple susceptibility loci, combinations of which contribute to the development of this disorder. We previously reported the results of a systematic survey of the human genome for the identification of highly informative DNA polymorphisms (SSTRPs) that target new AD risk genes. In addition to the APOE locus, our survey detected five new candidate susceptibility loci for AD, including D10S1423. An association of the D10S1423 234-bp allele with AD has been reported in three independent samples of AD cases and controls (Boston, Pittsburgh, Bonn). Data from our case-control studies suggest a strong synergistic interaction between the D10S1423 234-bp and APOE E4 risk alleles (234-bp carrier: OR = 2.5, 95% CI = 1.4--4.5; E4 carrier: OR = 8.3, 95% CI = 4.3--15.8; both alleles: OR = 23.1, 95% CI = 5.3--99.5). This report describes the prospective, longitudinal, double-blind assessment of the age-specific risk of AD encountered by 325 asymptomatic first-degree relatives of AD probands who carried the D10S1423 234-bp allele, the APOE E4 allele, or both, after 11.5 years of systematic follow-up. A total of 18 incident cases of AD were detected during the first 3379 subject-years of this longitudinal study. The effects of carrying either or both of the D10S1423 234-bp and APOE E4 alleles on the age-specific risk of developing AD were determined using Kaplan-Meier survival analysis. The age-specific risk of developing AD was the greatest for individuals who carried both alleles (Mantel--Cox statistic = 20.12, df = 3, P = 0.0002; Breslow statistic = 13.36, df = 3, P = 0.004). Cox proportional hazards models were developed to estimate the risk ratios for each genotype, controlling for the potential effects of age at recruitment, sex, and years of education. In the resulting best fitting model, only individuals who carried both risk alleles exhibited a risk ratio that differed significantly from 1 (risk ratio = 16.2, P = 0.008, 95% CI = 2.1--128.3). After controlling for these genotypes, female gender was also significantly associated with increased risk of developing AD (risk ratio = 5.1, P = 0.02, 95% CI = 1.2--21.1). Neither age at recruitment nor years of education made significant contributions to the model.

Do susceptibility loci contribute to the expression of more than one mental disorder? A view from the genetics of Alzheimer's disease

The susceptibility of developing most major psychiatric disorders is determined in part by contributions from risk alleles at multiple genetic loci. The central aim of this article is to highlight evidence from studies of neurodegenerative disorders suggesting that some of these alleles are shared by more than one psychiatric disorder, and to explore mechanisms that may underly these pleiotropic effects. The identification of constellations of susceptibility alleles associated with particular mental disorders will provide opportunities for new insights into the molecular and cellular pathophysiology of these disorders, and will have a major impact on psychiatric research and clinical care. This approach to reducing the variance in etiopathogenesis is also likely to be important for achieving the optimal use of available treatments (maximizing effectiveness and minimizing side effects), and for the discovery of novel medications or other interventions.

Clinical and neurobiological correlates of D10S1423 genotype in Alzheimer's disease

BACKGROUND

In a previous genome survey, we detected associations of alleles at six microsatellite loci with typical-onset AD, including the 234bp allele of the D10S1423 locus. The goal of the current study was to explore the clinical, neuropathological, and neurochemical correlates of the D10S1423 234bp allele in a group of 50 autopsy-confirmed cases of Alzheimer's disease (AD) who lacked other brain diseases.

METHODS

Clinical assessments were performed as part of a longitudinal study of AD and related disorders. Autopsies were performed using standardized methods and diagnoses were made according to established criteria. Genotyping, morphometry, and neurochemical analyses were performed using postmortem brain tissue.

RESULTS

Patients with AD who carried the D10S1423 234bp allele manifested substantial reductions in dopamine levels in all six cortical regions examined. In contrast, carriers tended to have higher concentrations of cortical norepinephrine and revealed a dosage effect of the D10S1423 234bp allele.

CONCLUSIONS

These findings support the results of our genome survey and suggest that a novel susceptibility gene for AD resides near the D10S1423 locus. The characterization of biologically meaningful subtypes, including genotypic subtypes with particular neurobiological derangements, may be important for the advancement of experimental therapeutics in AD.

Influence of APOE genotype on familial aggregation of AD in an urban population

OBJECTIVE

To examine the influence of the proband's APOE genotype on AD among first-degree relatives in a community-based study of African Americans, whites, and Caribbean Hispanics.

METHODS

History of AD and demographic information were obtained on 1,073 siblings and parents of 312 patients with AD and 2,722 siblings and parents of 802 nondemented controls. APOE genotyping was performed on all 1,114 patients and controls.

RESULTS

A higher proportion of patients with AD (35%) than controls (27%) had one or more APOE-epsilon4 alleles (p = 0.03). When compared with relatives of controls without an APOE-epsilon4 allele, the risk for AD was increased in first-degree relatives of both patients (rate ratio [RR] = 1.9, 95% confidence interval [CI] = 1.2 to 3.1) and controls (RR = 1.8, 95% CI = 1.2 to 2.6) with one or more APOE-epsilone alleles, regardless of ethnic group. There was a similar trend of increased risk in relatives of patients without an APOE-epsilon4 allele, but this was limited to Hispanics and African Americans.

CONCLUSIONS

The presence of an APOE-epsilon4 allele increases risk for AD among first-degree relatives, regardless of the probands' disease status, among all ethnic groups. Relatives of patients without an APOE-epsilon4 allele were also at increased risk for AD among Hispanics and African Americans, suggesting that other genes or risk factors may influence risk.

Clinical and neurobiological correlates of DXS1047 genotype in Alzheimer's disease

BACKGROUND

The goal of the current study was to explore the clinical, neuropathological, and neurochemical correlates of the DXS1047 202 bp allele in a group of 50 autopsy-confirmed cases of Alzheimer's disease (AD) who lacked other concomitant brain diseases. We previously published the results of a genome survey for novel risk loci for typical-onset (> or = 60 years) AD conducted at 10 cM resolution (Zubenko et al 1998a, b). This survey detected associations of alleles at six microsatellite loci with AD, including the 202 bp allele of the DXS1047 locus that resides within Xq25 on the human cytogenetic map.

METHODS

Clinical assessments were performed as part of a longitudinal study of AD and related disorders. Autopsies were performed using standardized methods and the resulting diagnoses were made according to established criteria. Genotyping, morphometry, and neurochemical analyses were performed using postmortem brain tissue.

RESULTS

Patients with AD who carried the DXS1047 202 bp allele manifested cortical norepinephrine levels that ranged from 2.1 to 3.6 times the corresponding values for noncarriers (p = .002), controlling for the potential effects of gender, age at symptomatic onset or death, and postmortem interval. In contrast, carriers tended to have lower cortical levels of dopamine (p = .10).

CONCLUSIONS

These findings support the results of our previous genome survey and suggest that the DXS1047 locus, or a locus in close proximity, modulates biological variables relevant to the pathophysiology of AD. In addition to providing insights into the clinical biology of AD, the characterization of biologically meaningful subtypes, including genotypic subtypes associated with particular neurobiological derangements, may be important to the advancement of experimental therapeutics in AD.

Risk of dementia in parents of probands with and without the apolipoprotein E4 allele. The EVA study

STUDY OBJECTIVE

Age, family history of dementia and the epsilon 4 allele of the apolipoprotein E gene have been associated with Alzheimer's disease (AD). Considering the strength of APOE-epsilon 4 as a genetic risk factor for AD, this factor might explain a large part of the association between AD and a family history of dementia. Therefore, in the general population, a higher frequency of dementia should be observed among parents of probands with at least one epsilon 4 allele than in parents of probands without this allele.

DESIGN, SETTING, AND PARTICIPANTS

The study investigated a sample of 1153 volunteers between 59 and 71 years old, genotyped for the APOE gene, all participating in the EVA study. Dementia in their parents was determined using a self reported questionnaire.

MAIN RESULTS

The frequency of dementia in 2164 parents was examined and it was found that 245 were demented. The percentage of demented parents was 13.0% in the subgroup of parents of subjects having one or two epsilon 4 alleles and 10.8% in the other subgroup. The relative risk of dementia among parents according to the APOE-epsilon 4 status of probands, was calculated using a Cox model adjusted for the educational level of parents and their history of stroke: RR = 1.21 (95% CI 0.90, 1.63).

CONCLUSION

This lack of association supports the observation that in the general population, APOE-epsilon 4 cannot explain a large part of family history of dementia.

Neurobiological correlates of a putative risk allele for Alzheimer's disease on chromosome 12q

OBJECTIVE

To explore the clinical, neuropathologic, and neurochemical correlates of the D12S1045 91 base pair (bp) allele in a group of 50 autopsy-confirmed cases of AD who lacked other concomitant brain diseases.

BACKGROUND

In a previous genome survey for novel risk loci for typical-onset (> or =60 years) AD conducted at 10 cM resolution, we detected associations of alleles at six microsatellite loci with AD. These included the 91bp allele of the D12S1045 locus that resides in the telomeric region of 12q.

METHODS

Clinical assessment was performed as part of a longitudinal study of AD and related disorders. Standardized pathologic methods, genotyping, morphometry, and neurochemical analyses were performed with postmortem brain tissue.

RESULTS

Patients with AD who carried the D12S1045 91bp allele manifested earlier ages at symptomatic onset and death, greater densities of cortical neurofibrillary tangles, and substantially greater reductions in cortical dopamine levels compared to noncarriers. A dosage effect of the number of D12S1045 91bp alleles on cortical dopamine levels was also observed.

CONCLUSIONS

Carrying the D12S1045 91bp allele was associated with greater clinical, neuropathologic, and neurochemical severity independent of sex and APOE genotype. These findings suggest that a novel susceptibility gene for AD resides at or in close proximity to the D12S1045 locus.

Apolipoprotein E genotype and noncognitive symptoms in Alzheimer's disease

BACKGROUND

The apolipoprotein E (ApoE) epsilon 4 allele confers significant risk for Alzheimer's disease and is associated with a greater amyloid burden in the brain. Future treatments may target molecular mechanisms associated with this allele, and it is important to define any phenotypic characteristics that correspond to this genotype. We sought to clarify the relationship between ApoE status and noncognitive symptoms in Alzheimer's disease patients.

METHODS

Possible and probable Alzheimer's disease patients from a clinical trial (n = 605) were assessed with the 10-item Neuropsychiatric Inventory cross-sectionally prior to treatment, and their ApoE genotype was determined. Among the population studied, the following numbers with specific genotypes were studied: 23-2/3, 17-2/4, 209-3/3, 288-3/4, 68-4/4.

RESULTS

When correlations were controlled for the patient's level of cognitive impairment, there was no relationship between epsilon 4 dose and any of the 10 noncognitive symptoms assessed, including psychosis, mood changes, and personality alterations.

CONCLUSIONS

Among patients with comparable disease severity, the epsilon 4 allele does not confer additional psychiatric morbidity.

Apolipoprotein E epsilon 4 allele and Japanese late-onset depressive disorders

BACKGROUND

Several studies have suggested that late-onset depressive disorder (LOD) and the apolipoprotein E (Apo E) epsilon 4 allele are associated with dementia, respectively. The Apo E polymorphism is significantly heterogeneous among races. We hypothesized that the Apo E epsilon 4 allele frequency is elevated in Japanese LOD.

METHODS

The Apo E genotype was studied in 134 patients (male, 53; female, 81) with early-/late-onset depressive disorder and 105 healthy normal controls (male, 41; female, 64). The patients were subdivided into those with early onset and late onset using 45 and 50 years as the cutoff ages. All the subjects were Japanese.

RESULTS

There was statistically no difference between normal control subjects and patients with depressive disorders in Apo E genotype or allele frequency. There was statistically no difference in the age of onset of depressive disorders according to the Apo E genotype. There was no relation between the age of onset of depressive disorder and the number of epsilon 4 alleles the patient had. There was also no association between early-/late-onset depressive disorder and the Apo E genotype or allele frequency.

CONCLUSIONS

Our results suggest that there is no association between the Apo E epsilon 4 allele and Japanese LOD.

Apolipoprotein E epsilon 4 allele in association with global cognitive performance and CSF markers in Alzheimer's disease

To better define the influence of apolipoprotein E (ApoE) epsilon 4 genotype on the cognitive and biochemical features of Alzheimer's disease (AD), cross-sectional analysis of global cognitive measures and cerebrospinal fluid studies gathered on AD subjects at a tertiary care facility between 1986 and 1997 was carried out. The 112 AD patients examined included 62 women and 50 men with a mean (SD) age of 64.2 (9.2) years. Patient demographics; illness onset age and duration, education level and global cognitive measures were recorded systematically. Genetic analysis for ApoE allele type and biochemical characterization of CSF, including total tau concentration, was performed. Descriptive statistics of demographics, cognitive and CSF measures were performed by chi-square, ANOVA and Tukey's tests. Overrepresentation of the epsilon 4 allele was found, with 45.5% of AD patients heterozygous and 20.5% homozygous for ApoE epsilon 4. Overall, ApoE epsilon 4 status had no effect on mean onset age of AD (F = 1.56; p = 0.214), but an earlier mean onset age of AD (F = 4.10; p = 0.02) was seen in the late-onset subjects. No differences were found with regard to ApoE epsilon 4 status and measures of disease, duration of illness or global cognitive performance. Although CSF tau was elevated in our sample (575.4 +/- 290.3 pg/ml), ApoE epsilon 4 status did not influence total CSF tau or neurotransmitter metabolite levels. ApoE epsilon 4 genotype had no impact on a variety of illness severity, cognitive and CSF examinations in the largest cross-sectional analysis of AD subjects yet reported.

High frequency of apolipoprotein E epsilon4 allele in young individuals with very mild Alzheimer's disease-related neurofibrillary changes

The pathological process of initial neurofibrillary (NF) changes underlying Alzheimer's disease (AD) represents the early preclinical phase of the disease. In a small percentage of individuals, these initial NF changes (Braaks' stage I of six stages) may develop at a surprisingly young age. The aim of this study was to determine the impact of apolipoprotein E (ApoE) on the development of such initial NF changes in young individuals. To this end, the ApoE genotypes were determined using a seminested polymerase chain reaction assay followed by restriction isotyping in young individuals (n = 44; mean age of 38 years) with initial NF changes (stage I). The results were compared with ApoE genotypes of age-matched controls (n = 70) devoid of such changes (stage 0). Stage I cases exhibited a significantly higher epsilon4 allele frequency compared to controls (0.18 vs 0.09, P = 0.039). Thus, the present study reveals an association of epsilon4 allele with the early onset of AD-related NF changes in young individuals. This finding underlines the relevance of the asymptomatic phase in the course of AD.

A genome survey for novel Alzheimer disease risk loci: results at 10-cM resolution

We completed a systematic survey of the human genome, conducted at an average resolution of 10 cM, for the identification of simple sequence tandem repeat polymorphisms (SSTRPs) that target new risk genes for Alzheimer disease (AD) by virtue of linkage disequilibrium. The efficiency of our association study was enhanced by genotyping pools of DNA from autopsy-confirmed cases with AD and matched controls. Allelic associations with AD were observed for 6 of the 391 SSTRPs in the CHLC Human Screening Set/Weber Version 6 (Research Genetics, Inc., Huntsville, AL): D1S518, D1S547, D10S1423, D12S1045, D19S178, and DXS1047. These allelic associations were replicated in an independent sample of autopsied AD cases and controls recruited from a geographically disparate site. The association of the large D19S178 alleles with AD appeared to arise from linkage disequilibrium with the APOE epsilon 4 allele, whose effect on increasing the risk of AD has been established. None of the remaining SSTRPs was in close proximity to loci previously reported to influence the risk of developing AD. Instead, they may identify five novel AD susceptibility loci.

Initial results of a genome survey for novel Alzheimer's disease risk genes: association with a locus on the X chromosome

As the initial step in a systematic genome survey, 16 simple sequence tandem repeat polymorphisms that span the X chromosome at an average spacing of 10 cM were examined for allelic associations with typical-onset Alzheimer's disease (AD). The efficiency of this survey was substantially enhanced by genotyping pools of genomic DNA from 50 autopsy-confirmed AD cases and 50 autopsied controls who were similar in sex ratio, race, and age at death. The frequency of the DXS1047 202-bp allele was twice as common among AD cases (0.45+/-S.E. 0.06) than controls (0.22+/-S.E. 0.05), a finding that was reproduced in an independent and geographically disparate sample. Consistent with Hardy-Weinberg equilibrium, the proportion of women with AD who carried the 202-bp allele, 73% was nearly double that observed for men with AD, 38%. However, the frequency of the 202-bp allele was similar for men and women and the presence of this allele did not affect the age at onset of dementia in either sex. Furthermore, the frequency of the DXS1047 202-bp allele in AD cases and controls was unaffected by the APOE genotype, indicating that these two loci modulate AD risk independently. Finally, the frequency of the 202-bp allele among 50 autopsy-confirmed cases of Parkinson's disease (0.29+/-S.E. 0.06) was indistinguishable from the control value, reflecting relative specificity for this allelic association with AD.

Multiple threshold model for the onset of Alzheimer's disease in the NAS-NRC twin panel

The three common alleles at the APOE locus influence the onset and lifetime risk of typical late-onset Alzheimer's disease (AD). Other loci may also alter risk of late-onset AD. One may assess the relative influence of APOE on the genetic contribution to AD by estimating the proportion of AD heritability that is explained by APOE polymorphism. To do this requires an initial estimate of the heritability of AD. Traditional methods are not appropriate for this estimation since they do not consider right-censoring (incomplete expression of the genotype owing to death) nor do they model the relation of onset age and disease liability. Here we present an analytic model that addresses both of these issues. Genetic and environmental influences on AD are examined by assuming that onset of dementia in AD is a late event in an extended degenerative process where earlier onset reflects a more rapid course of neurodegeneration. The model is fitted to the occurrence of AD among 9,786 members of the National Academy of Sciences-National Research Council Registry of aging veteran twins. When both additive genetic and common environmental effects are used in the model, they explain 37% and 35%, respectively, of the variation in AD onset. Given the limited numbers of AD cases now available, models containing only additive genetic or shared environmental effects (explaining 75% and 65% of individual differences in disease onset, respectively) cannot be rejected in favor of a model that retains both influences.

Gender effect on apolipoprotein E epsilon4 allele-associated risk for sporadic Alzheimer's disease

INTRODUCTION

The role of gender in Alzheimer's disease (AD), and its possible interaction with apolipoprotein E (apoE), has been controversial.

MATERIAL AND METHODS

ApoE allelic frequencies and the effect of apoE epsilon4 allele dosage on risk and age at onset of AD were evaluated, separately for men and women, in 100 patients with sporadic AD and 100 age-matched controls.

RESULTS

The distribution of apoE alleles and the odds ratio for AD, when associated with 1 or 2 epsilon4 alleles, were not statistically different between men and women. No effect of the dosage of the epsilon4 allele was found on the age at onset of dementia in the 2 sex groups.

CONCLUSION

Our data suggest that the relation of the apoE genotype to AD is not dependent on sex.

The National Institute on Aging/Alzheimer's Association recommendations on the application of apolipoprotein E genotyping to Alzheimer's disease

In a conference held in Chicago during October 1995, a working group of the National Institute of Aging (NIA) and the Alzheimer's Association (AlzA) drafted consensus recommendations on research and clinical applications of APOE genetic susceptibility testing for Alzheimer's disease (AD). The NIA/AlzA Working Group concluded that in considering future applications of APOE genotyping and other knowledge that has been gained about the genetic basis of AD, the interests of AD patients and their family members must be held paramount. The group acknowledged that a robust association exists between possession of the APOE epsilon 4 allele and the risk of late-onset AD and cited evidence that this allele is more strongly associated with AD than any other form of dementia. They recommended against the use of APOE genotyping to predict the-future development of AD in asymptomatic individuals at this time, and warned against the use of the test in isolation as the sole means for diagnosing AD. The group endorsed the concept of discretionary use of APOE genotyping as an adjunct to other AD diagnostic procedures. However, routine clinical use of the test for this purpose was not recommended at this time. Physicians were advised to weigh any potential benefits of testing against the possibility that genotype disclosure could adversely affect the insurability, employability, and social standing of AD patients and their family members. Adequate provisions for pre-test and post-test counseling and psychosocial support were advised for all future clinical and research applications of APOE genotyping. The group called for the development of improved protocols for AD genetic counseling as well as supplemental measures to assure genetic privacy for AD patients and their family members.

Association of the APOE epsilon 4 allele with clinical subtypes of late life depression

The APOE genotypes of 45 elderly inpatients with major depression were determined to investigate the relationship of this disorder to irreversible dementia in late life. We specifically tested the hypothesis that the frequency of the APOE epsilon 4 allele is elevated in depressed elders with cognitive impairment or psychotic features, subtypes that have been reported to be at increased risk of developing Alzheimer's disease (AD). The frequency of epsilon 4 allele was not elevated in the overall group of 45 inpatients and, contrary to our expectation, was not associated with cognitive impairment in this group. In contrast, the epsilon 4 allele frequency for the patients with psychotic features was nearly four times that for the patients without psychotic features and nearly double that of elderly controls. These data suggest that elderly depressed inpatients with cognitive impairment are at risk for developing AD by an epsilon 4-independent pathway, while those with psychotic features are at risk for developing AD by an epsilon 4-dependent pathway. These findings suggest that subtypes of idiopathic major depression in late life may serve as landmarks that distinguish separable pathogenetic pathways to AD.

[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.

The frequency of apolipoprotein E4 allele is not increased in patients with probable vascular dementia

We used the NINDS-AIREN criteria to diagnose vascular dementia (VD), and compared apolipoprotein E (apoE) allele frequencies and apoE concentrations in serum and cerebrospinal fluid (CSF) between patients with possible (n = 19) and probable (n = 33) VD and controls (n = 105). There was no difference in apoE4 frequency between patients with probable VD and controls. Serum and CSF apoE concentrations did not differ between VD patients and controls. Our results suggest that apoE plays no role in the development of VD.

Neuropathological evaluation and apolipoprotein E gene polymorphism analysis in diffuse Lewy body disease

We performed a quantitative neuropathological investigation of senile plaques and neurofibrillary tangles in the brains of 14 Japanese patients with diffuse Lewy body disease (DLBD), and examined apolipoprotein E (APOE) gene polymorphism in these patients. Most DLBD brains had as many senile plaques as those with Alzheimer-type dementia (ATD), but fewer neurofibrillary tangles. The APOE epsilon 4 allele frequency in DLBD was 39.3%, similar to that previously reported in pathologically diagnosed ATD. DLBD and ATD are clinically and pathologically distinct, but may have common mechanisms with regard to the formation of amyloid deposition based on these findings. Future investigation of the pure form of DLBD may clarify the association between Lewy body dementia and APOE.

Apolipoprotein E-epsilon 4 allele and familial risk in Alzheimer's disease

Recent studies have found an association between presence of apolipoprotein E (APOE) epsilon 4 allele and Alzheimer's disease (AD). The present study compared the cumulative risk of primary progressive dementia (PPD) in relatives of AD probands carrying at least one copy of the epsilon 4 allele with the relatives of AD probands not carrying epsilon 4 and with relatives of non-demented controls. Our aim was to determine whether the familial aggregation of PPD in relatives of AD probands is primarily due to those carrying epsilon 4. Seventy-seven neuropathologically diagnosed AD patients were obtained as probands through our Alzheimer's Disease Research Center Brain Bank. AD probands were genotyped for APOE. As a comparison group, 198 non-demented probands were also included. Through family informants, demographic and diagnostic data were collected on 382 first-degree relatives (age > or = 45 years) of AD probands and 848 relatives of the controls. We found that the cumulative risk of PPD in both relatives of AD probands with and without the epsilon 4 allele was significantly higher than that in the relatives of non-demented controls. However, the increased risk in the relatives of AD probands with the epsilon 4 allele was marginally, but not significantly, lower than the risk in the relatives of probands without epsilon 4. A greater likelihood of death by heart diseases over developing PPD in relatives of AD probands with epsilon 4 (3.1-fold increase) was found compared to relatives of probands without epsilon 4 (1.7-fold increase), especially prior to age 70, although the difference was not statistically significant. The increased familial risk for PPD in the relatives of AD probands with the APOE-epsilon 4 allele relative to controls suggests that familial factors in addition to APOE-epsilon 4 are risk factors for AD. Differential censorship from increased mortality of heart diseases may have prevented a higher incidence of PPD among the relatives of probands with epsilon 4.

Apolipoprotein E in the genetics and epidemiology of Alzheimer's disease

The role of apolipoprotein E (ApoE) alleles and isoforms in the etiology and pathogenesis of Alzheimer's disease is discussed. The possibility that ApoE itself is not involved in the disease pathogenesis but is merely in genetic disequilibrium with the real locus is discussed and dismissed. The data showing that the epsilon 4 allele is associated with an increased risk of developing the disease and with an earlier onset age are reviewed. The data showing that, at least in some circumstances, the epsilon 2 allele is associated with a decrease in the risk of developing the disease, and with a later onset age are also reviewed. Data from the genetic analysis of other disorders are reviewed and presented, and it is suggested that the genetic data support the notion that the role of ApoE in the etiology of the disease directly relates to beta-amyloid deposition and plaque formation. This suggestion is in concordance with the most likely mechanism for the role of beta-amyloid precursor protein gene mutations as other risk factors for the disease.