Apolipoprotein E epsilon 4 allele is a risk factor for familial and sporadic presenile Alzheimer's disease in both homozygote and heterozygote carriers

Relationship Between Genetic Variants of ACAT1 and APOE with the Susceptibility to Dementia (SADEM Study)

One of the hypotheses that have emerged to explain the origin of dementia relates the disease with altered lipid metabolism, particularly cholesterol. To maintain cholesterol homeostasis, the ACAT1 enzyme has an important function to regulate the production of Aβ. Moreover, APOE is the main cholesterol carrier in the brain, and it has been reported as a risk factor for this disease. This study evaluates the relationship between ACAT1 and APOE genetic variants with susceptibility for the development of Alzheimer's disease and other dementias. We examined four ACAT1 polymorphisms (rs2247071, rs2862616, rs3753526, rs1044925) and two in the APOE gene (rs7412, rs429358) in a group of 204 controls and 196 cases of dementia. Our results show one protective haplotype: CGCA (OR = 0.34, 95% CI = 0.23-0.46; p < 0.001) and one risk haplotype: CGGA (OR = 1.87, 95% CI = 1.34-2.60; p < 0.001) for the development of dementia. Subjects identified as APOE-ε4 allele carriers had a higher risk of developing dementia compared with non-carriers, OR = 13.33 (95% CI = 3.14-56.31). The results support the hypothesis that the ACAT1 gene, together with the APOE gene, plays an important role in susceptibility to the development of dementia and shows genetic characteristics of the Mexican population that can be used to identify the population at risk.

ACAT1 as a Therapeutic Target and its Genetic Relationship with Alzheimer's Disease

BACKGROUND

Alzheimer´s disease (AD) is a chronic and progressive disease which impacts caregivers, families and societies physically, psychologically and economically. Currently available drugs can only improve cognitive symptoms, have no impact on progression and are not curative, so identifying and studying new drug targets is important. There are evidences which indicate disturbances in cholesterol homeostasis can be related with AD pathology, especially the compartmentation of intracellular cholesterol and cytoplasmic cholesterol esters formed by acyl-CoA: cholesterol acyltransferase 1 (ACAT1) can be implicated in the regulation of amyloid-beta (Aβ) peptide, involved in AD. Blocking ACAT1 activity, beneficial effects are obtained, so it has been suggested that ACAT1 can be a potential new therapeutic target. The present review discusses the role of cholesterol homeostasis in AD pathology, especially with ACAT inhibitors, and how they have been raised as a therapeutic approach. In addition, the genetic relationship of ACAT and AD is discussed.

CONCLUSION

Although there are several lines of evidence from cell-based and animal studies that suggest that ACAT inhibition is an effective way of reducing cerebral Aβ, there is still an information gap in terms of mechanisms and concerns to cover before passing to the next level. Additionally, an area of interest that may be useful in understanding AD to subsequently propose new therapeutic approaches is pharmacogenetics; however, there is still a lot of missing information in this area.

Seasonal distribution of births in patients with Alzheimer’s disease and elderly depressive patients

Winter births have been associated with a higher risk of Alzheimer’s disease (AD) and other psychiatric disorders. In the present investigation, this putative association was examined in a sample of gerontopsychiatric patients. An analysis of the quarterly birth rates of 83 patients with AD, 78 elderly depressive patients with an early onset and 74 patients with a late onset of the depressive disorder, 48 patients with both AD and depression (co-morbid patients) and 107 healthy control subjects, revealed no particular seasonal distribution for any of the diagnostic groups. In AD and co-morbid patients, controlling for the ApoE genotype did not change this finding. Logistic regression analysis revealed the expected findings that increasing age and the presence of the ApoE4 allele were associated with a higher risk of dementia. Younger age and female gender were identified as risk factors for a depressive disorder. A winter birth (birth in the first three months of the year) was not associated with any of the diagnostic subgroups.

We concluded that in our sample a seasonal distribution of births was not found to increase the risk for AD or geriatric depression.

The Genetics of Alzheimer's Disease in the Chinese Population

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by progressive cognitive dysfunction and behavioral impairment. In China, the number of AD patients is growing rapidly, which poses a considerable burden on society and families. In recent years, through the advancement of genome-wide association studies, second-generation gene sequencing technology, and their application in AD genetic research, more genetic loci associated with the risk for AD have been discovered, including KCNJ15, TREM2, and GCH1, which provides new ideas for the etiology and treatment of AD. This review summarizes three early-onset AD causative genes (APP, PSEN1, and PSEN2) and some late-onset AD susceptibility genes and their mutation sites newly discovered in China, and briefly introduces the potential mechanisms of these genetic susceptibilities in the pathogenesis of AD, which would help in understanding the genetic mechanisms underlying this devastating disease.

Population-based analysis of Alzheimer's disease risk alleles implicates genetic interactions

BACKGROUND

Reported odds ratios and population attributable fractions (PAF) for late-onset Alzheimer's disease (LOAD) risk loci (BIN1, ABCA7, CR1, MS4A4E, CD2AP, PICALM, MS4A6A, CD33, and CLU) come from clinically ascertained samples. Little is known about the combined PAF for these LOAD risk alleles and the utility of these combined markers for case-control prediction. Here we evaluate these loci in a large population-based sample to estimate PAF and explore the effects of additive and nonadditive interactions on LOAD status prediction performance.

METHODS

2419 samples from the Cache County Memory Study were genotyped for APOE and nine LOAD risk loci from AlzGene.org. We used logistic regression and receiver operator characteristic analysis to assess the LOAD status prediction performance of these loci using additive and nonadditive models and compared odds ratios and PAFs between AlzGene.org and Cache County.

RESULTS

Odds ratios were comparable between Cache County and AlzGene.org when identical single nucleotide polymorphisms were genotyped. PAFs from AlzGene.org ranged from 2.25% to 37%; those from Cache County ranged from .05% to 20%. Including non-APOE alleles significantly improved LOAD status prediction performance (area under the curve = .80) over APOE alone (area under the curve = .78) when not constrained to an additive relationship (p < .03). We identified potential allelic interactions (p values uncorrected): CD33-MS4A4E (synergy factor = 5.31; p < .003) and CLU-MS4A4E (synergy factor = 3.81; p < .016).

CONCLUSIONS

Although nonadditive interactions between loci significantly improve diagnostic ability, the improvement does not reach the desired sensitivity or specificity for clinical use. Nevertheless, these results suggest that understanding gene-gene interactions may be important in resolving Alzheimer's disease etiology.

Role of the Transforming-Growth-Factor-β1 Gene in Late-Onset Alzheimer's Disease: Implications for the Treatment

Late-onset Alzheimer's disease (LOAD) is the most common form of dementia in the elderly. LOAD has a complex and largely unknown etiology with strong genetic determinants. Genetics of LOAD is known to involve several genetic risk factors among which the Apolipoprotein E (APOE) gene seems to be the major recognized genetic determinant. Recent efforts have been made to identify other genetic factors involved in the pathophysiology of LOAD such as genes associated with a deficit of neurotrophic factors in the AD brain. Genetic variations of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), and transforming-growth-factor-β1 (TGF-β1) are known to increase the risk to develop LOAD and have also been related to depression susceptibility in LOAD. Transforming-Growth-Factor-β1 (TGF-β1) is a neurotrophic factor that exerts neuroprotective effects against ß-amyloid-induced neurodegeneration. Recent evidence suggests that a specific impairment in the signaling of TGF-β is an early event in the pathogenesis of AD. TGF-β1 protein levels are predominantly under genetic control, and the TGF-β1 gene, located on chromosome 19q13.1–3, con-tains several single nucleotide polymorphisms (SNPs) upstream and in the transcript region, such as the SNP at codon +10 (T/C) and +25 (G/C), which is known to influence the level of expression of TGF-β1. In the present review, we summarize the current literature on genetic risk factors for LOAD, focusing on the role of the TGF-β1 gene, finally discussing the possible implications of these genetic studies for the selection of patients eligible for neuroprotective strategies in AD.

Polymorphisms of APOE and LRP genes in Brazilian individuals with Alzheimer disease

Alzheimer disease (AD) is the most frequent cause of dementia in Western countries. Putative genetic risk factors for AD are polymorphisms in the apolipoprotein E (APOE) gene and in the low-density lipoprotein receptor-related protein (LRP) gene. Our objective was to investigate the role of the APOE coding region polymorphisms epsilon 2, epsilon 3, and epsilon 4 and APOE promoter variants A/T at position -491 and G/T at -219, as well as LRP polymorphism C/T, as risk factors for AD in Brazilian individuals. One hundred and twenty patients with probable AD, along with 120 controls were analyzed. A significant difference between patients and controls for epsilon 4 alleles was observed: frequency of this allele in AD was 0.31, and 0.10 in controls. Individuals with 2 epsilon 4 alleles had a higher risk for AD than subjects with only 1 such allele; presence of 1 epsilon 2 allele proved protective. The presence of the T allele of the -219 polymorphism was also associated with an increased risk of AD, but this polymorphism is in linkage disequilibrium with APOE epsilon polymorphisms. No significant differences between patients and controls were observed for -491 APOE or LRP polymorphisms. In this Brazilian population, both the epsilon 4 allele and T -219 polymorphism were associated with an increased risk for AD.

Sex influences on cholinesterase inhibitor treatment in elderly individuals with alzheimer's disease

BACKGROUND

The second generation of cholinesterase inhibitors (ChEIs) is approved in the United Kingdom for the treatment of mild to moderate Alzheimer's disease (AD). The UK National Institute of Clinical Excellence has raised questions, however, about whether ChEIs are cost-effective for the treatment of dementia. To address these concerns, it is important to identify factors that predict which patients may have the best response to ChEl treatment.

OBJECTIVE

We reviewed animal studies and human clinical studies to address whether sex can predict and influence the response to ChEI treatment based on differences in neuroanatomy, pharmacokinetics, and prevalence of dementia.

METHODS

Relevant articles examining the use of ChEIs in humans with dementia (especially in AD) and in animals were identified through searches of several databases, including MEDLINE, PubMed, and EMBASE for general medical topics, the Cochrane Controlled Clinical Trials Register and CINAHL DIRECT for nursing and allied health issues, and PsycLIT for reviews of psychology and psychiatry topics (1980 June 2006). Articles reviewed were limited to those that discussed the use of ChEIs in relation to sex.

RESULTS

Animal studies have produced a substantial amount of evidence to support the hypothesis that sex may influence the response to ChEIs and, in particular, that testosterone may play a significant role in producing this difference by its influence on the entry of ChEIs into the brain. The results of clinical studies in humans, on the other hand, have been mixed. Two double-label and open-label clinical studies suggested that there may be a 3-way interaction between apolipoprotein E genotype, sex, and tacrine (range, P = 0.03 to P = 0.05). Seven double-blind, open-label clinical trials and 13 case studies of donepezil, rivastigmine, and galantamine produced little evidence of an association between treatment outcomes (as measured with clinical rating scales) and sex, although in an open-label 2-year study in women with AD treated with donepezil, women had lower mortality rates than men (10% and 20%, respectively; P = 0.003). One study produced weak evidence that women treated with ChEIs may experience more adverse effects than men, but this may have been attributable to low body weight rather than to sex differences.

CONCLUSIONS

A substantial relation has not been established between sex and the second-generation ChEIs currently used in clinical settings for the treatment of AD. If an interaction between sex and ChEI treatment does exist, as suggested in 10 of the studies we analyzed, it is likely to be small and subtle, with much individual variation, as is the case with most neurologic sex differences. Nevertheless, sexual dimorphism in response to ChEI therapy warrants further investigation, especially in regard to its role in the development of novel AD therapies.

Démarche diagnostique devant un syndrome démentiel

PURPOSE

The high prevalence of dementia, particularly of Alzheimer's disease, the increase of their incidence with age, and the population aging make this group of diseases a major problem for public health. Nevertheless, diagnosis is difficult because it depends on evolution of disturbances that patients often cannot precisely relate, on complex neuropsychological explorations, and on pathological examination difficult to obtain. Today in France, geriatricians are fully implicated in the diagnosis of dementia and all the physicians who give care to elderly, should lead easily a diagnosis of dementia.

CURRENT KNOWLEDGE AND KEY POINTS

In February 2000 ANAES (French governmental agency for accreditation and evaluation of health system) published recommendations called "practical recommendations for the diagnosis of Alzheimer's disease". These recommendations allow physicians to standardize their practices and consist of a rigorous clinical history and examination, a neuropsychological analysis, standard investigations and application of diagnostic criteria already widely diffused and used.

FUTURE PROSPECTS AND PROJECTS

Deepening of knowledge, in particular in the domains of neuropsychology and functional cerebral imagery, should allow physicians to diagnose early dementia. These early diagnosis should allow to initiate a multidisciplinary, preventive and effective care for patients. Specific drugs, that will be available, will be intended mostly for patients with early diagnosis, ideally at a pre-dementia state.

Age at onset is associated with disease severity in Lewy body variant and Alzheimer's disease

This study investigated the influence of age at onset on cognitive performance, neuropathological and neurochemical features in autopsy-confirmed sporadic Lewy body variant (LBV) and in Alzheimer's disease (AD). We compared 28 early-onset (< or = 70 years) LBV subjects with 28 matched late-onset (> 70 years) subjects. Similarly, we examined the same features in 89 early onset AD and 89 matched late onset AD patients. Patients with early onset LBV and early onset AD declined more rapidly, had more neuritic plaques, and greater neocortical cholinergic loss compared to late onset LBV and late onset AD subjects. Taken together, these results suggest that for both LBV and AD, earlier age at onset may predict a more aggressive disease course.

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.

Evaluation of multiple presenilin 2 SNPs for association with early-onset sporadic Alzheimer disease

The presenilin genes encode proteins that modify, mediate, or perform similar functions to gamma-secretase, the enzyme responsible for converting amyloid beta precursor protein (APP) into beta-amyloid. Mutations in the presenilin genes cause an increased production of Abeta42, the aberrant form of beta-amyloid found in the neural plaques of Alzheimer disease patients. Previously reported association studies of presenilin 2 (PSEN2) polymorphisms with early-onset Alzheimer disease (EOAD) have produced contradictory results. In an effort to resolve these differences, we tested eight single nucleotide polymorphisms in and around the 3' region of the PSEN2 gene for association with EOAD. An initial set of Scottish EOAD cases (n = 121) and controls (n = 152) was screened using the genotyping method dynamic allele-specific hybridization (DASH). No significant differences were seen between allele or genotype frequencies of cases and controls. However, when conditioned on the risk allele (epsilon 4) APOE, three polymorphisms showed allelic association with a P value below 0.05. These same polymorphisms were in near 100% linkage disequilibrium with each other (P < 5 x 10(-5)), and in each, one of the homozygous genotypes was absent in controls but present in the cases. Replication in an independent set of Scottish EOAD cases (n = 84) and controls (n = 173) did not confirm this finding. From this study we find no evidence to suggest that variations in the PSEN2 gene pose as major risk factors for sporadic EOAD.

Human leucocyte antigen-A2 increases risk of Alzheimer's disease but does not affect age of onset in a Scottish population

The use of non-steroidal anti-inflammatory drugs has been associated with a reduced incidence of Alzheimer's disease (AD), suggesting that attenuation of the inflammatory response may be beneficial. Several, but not all, genetic association studies have shown human leucocyte antigen (HLA)-A2, a major histocompatibility complex class I antigen-binding transmembrane protein has an increased frequency in AD compared to controls, and in some reports is associated with a lowered age of onset. We further investigated the role of HLA-A2 in an independent sample of AD cases, including a large early onset cohort. The results of this current study and meta analysis of all studies available to date support previous evidence of an excess of HLA-A2 in AD, but found no evidence of a relationship with age of onset.

Analysis of the disease risk locus DXS1047 polymorphism in Brazilian Alzheimer patients

Alzheimer's disease (AD) is a disorder characterized by a progressive deterioration in memory and other cognitive functions. Four genes associated with early onset AD have been identified but familial AD is rare. The majority of late onset AD (LOAD) is caused by a complex inheritance with several genes interacting with environmental factors. The epsilon4 allele of the apolipoprotein E (APOE) gene has been reported worldwide as a risk factor associated with LOAD. The short variant of a polymorphism in the transcriptional region of the serotonin transporter gene (5-HTTLPR) was analyzed in several psychiatric conditions and found to be more frequently associated with European and Brazilian LOAD patients. Recently, allelic associations with LOAD were reported for five other loci, the most significant for one X-linked 202-bp allele, at the DXS1047 locus. We have analyzed this locus in Brazilian LOAD patients and observed that the 202-bp allele was not significantly more frequent among patients. In contrast, two other alleles (200 bp and 208 bp) were less frequent among AD male patients than in controls, confirming the importance of replicating association studies in different populations.

Uses of Evolutionary Theory in the Human Genome Project

▪ Abstract  The Human Genome Project (HGP) originally sought to sequence the human genome but excluded studies on genetic diversity. Now genetic diversity is a major focus, and evolutionary theory provides needed analytical tools. One type of diversity research focuses on complex traits. This is often done by screening genetic variation at candidate loci functionally related to a trait followed by gene/phenotype association tests. Linkage disequilibrium creates difficulties for association tests, but evolutionary analyses using haplotype trees can circumvent these problems and result in greater statistical power, better disease risk prediction, the elimination of some polymorphisms as causative, and physical localization of causative variation when combined with an analysis of recombination. The HGP also now proposes to map over 100,000 single nucleotide polymorphisms to test for gene/phenotype associations through linkage disequilibrium in isolated human populations affected by past founder or bottleneck events. This strategy requires prior knowledge of recent human evolutionary history and current population structure, but other evolutionary considerations dealing with disequilibrium and nonrandom mutation pose difficulties for this approach. Studies on population structure also focus upon traits of medical relevance, and an understanding of the evolutionary ultimate cause for the predisposition of some populations to certain diseases is a useful predictor for shaping public health policies. Studies on the genetic architecture of common traits reveal much epistasis and variation in norms of reaction, including drug response. Because of these interactions, context dependency and sampling bias exist in disease association studies that require population information for effective use. Overall, the population thinking of evolutionary biology is an important counterweight to naive genetic determinism in applying the results of the HGP to issues of human health and well-being.

Association between Alzheimer's disease and the NOS3 gene

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder of later life. Genetic studies have demonstrated that the apolipoprotein E (ApoE) gene is an important susceptibility locus; however, other environmental and genetic factors operating alone or in combination with ApoE must also be involved. Among candidate genes that may contribute to this residual risk is the endothelial nitric oxide synthase (NOS3) gene. NO release from vascular endothelium accounts in large part for endothelium-derived relaxing factor bioactivity. Abnormalities of cerebral small vessels occur early in AD, and it has been demonstrated recently that beta-amyloid interacts with endothelial cells in blood vessels to produce an excess of superoxide radicals. We have genotyped 122 cases of early-onset AD (EOAD) and 317 cases of late-onset AD (LOAD) as well as 392 controls for a common structural polymorphism Glu/Asp at codon 298 in the NOS3 gene. We find a highly significant enrichment for Glu/Glu homozygotes in LOAD compared with controls. The effect appears to be independent of ApoE status. NOS3 may be a new genetic risk factor for LOAD.

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.

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.

Apolipoprotein E gene in Parkinson's disease, Lewy body dementia and Alzheimer's disease

Apolipoprotein E (Apo E) epsilon 4 allele is a risk factor for early and late onset Alzheimer's disease. This prompted us to examine other neurophyschiatric phenotypes. Epsilon 4 allele was significantly enriched in Lewy body dementia (n = 39) but not in Parkinson's disease (n = 50) or Schizophrenia (n = 175) compared to aged non-demented controls (n = 47) and the Scottish population (n = 400). We conclude that Lewy body disease should be regarded as a variant of Alzheimer's but not Parkinson's disease.

The complexity of the genotype-phenotype relationship and the limitations of using genetic "markers" at the individual level

Many associations have recently been discovered between phenotypic variation and genetic loci, causing some to advocate what Robert Sinsheimer has called "a new eugenics" that would treat genetic "defects" in individuals prone to a disease. The first premise of this vision is that genetic association studies reveal the biological cause of the phenotypic variation. Once the responsible genes are known, the second premise is that we should focus upon changing "nature" rather than "nurture" by correcting the "defective" genes. The first premise is flawed because associations between genetic markers and phenotypes can be spurious, as shown by an example. Moreover, it is shown that using non-causative but associated genetic markers one at a time (the normal practice) can lead to incorrect predictions of disease risk for many individuals. Going from association to causation is a non-trivial step scientifically that has rarely been done in much of the human genetic research. Even when a particular locus does contribute to the phenotypic variation of interest, the first premise remains flawed because phenotypes in general arise from complex interactions among genes and between genes and environments as shown for genes associations with coronary artery disease (CAD). The ability of current molecular genetic tools to "fix" defective genotypes is extremely limited, but even if the technological problems could be overcome, the studies on CAD reveal no obvious "defective" gene to fix because the genetic effects are so context dependent (upon both other genes and environmental factors). Contrary to the second premise of the new eugenics, the more we learn about how different genotypes show variable responses to environments, the more important the environment becomes for individual treatment. The paradigm of a "defective gene" may work for classical Mendelian genetic diseases that are due to loss-of-function mutations. However, such mutations affect only a small portion of humanity. When the focus is changed to common disease and behavioral phenotypes, the "defective gene" paradigm is biologically meaningless and often harmful when applied to individuals. Thus, even when genes clearly do influence common phenotypic variation, the premises of the "new eugenics" are biologically indefensible.

A polymorphism in the presenilin 1 gene does not modify risk for Alzheimer's disease in a cohort with sporadic early onset

Mutations in the presenilin 1 gene account for many cases of early onset familial Alzheimer's disease. Homozygosity for the 'T' allele of a polymorphism in the presenilin 1 gene has previously been reported to double the risk for Alzheimer's disease in a late onset Caucasian sample. Here we report that this polymorphism does not incur risk in a case control sample of early onset Alzheimer's disease, possibly suggesting a different disease etiology between the early and late onset forms.

The genetics of dementia in late life

Recent advances in the genetics of AD and other late-life dementias have provided new insights but also have raised new queries and ethical issues. This review reflects the current state of knowledge in a rapidly evolving field. The complex relation of genes and environment to AD, VaD, and other late-life dementias suggests that the answers to these many issues will evolve through time. New issues undoubtedly will arise as additional genes are discovered and new data accrue that relate APOE and other genes to the mechanism and expression of dementing illness. The clinical relevance and applicability of such research findings will increase when effective treatments become available. Given this potential, we encourage readers to monitor new developments as they arise.

Apolipoprotein E and Alzheimer disease: genotype-specific risks by age and sex

The distribution of apolipoprotein E (APOE) genotypes as a function of age and sex has been examined in a French population of 417 Alzheimer disease (AD) patients and 1,030 control subjects. When compared to the APOE epsilon3 allele, an increased risk associated with the APOE epsilon4 allele (odds ratio [OR] [epsilon4] = 2.7 with 95% confidence interval [CI] = 2.0-3.6; P < .001) and a protective effect of the APOE epsilon2 allele (OR[epsilon2] = 0.5 with 95% CI = 0.3-0.98; P = .012) were retrieved. An effect of the epsilon4 allele dosage on susceptibility was confirmed (OR[epsilon4/epsilon4] vs. the epsilon3/epsilon3 genotype = 11.2 [95% CI = 4.0-31.6]; OR[epsilon3/epsilon4] vs. the epsilon3/epsilon3 genotype = 2.2 [95% CI = 1.5-3.5]). The frequency of the epsilon4 allele was lower in male cases than in female cases, but, since a similar difference was found in controls, this does not lead to a difference in OR between sex. ORs for the epsilon4 allele versus the epsilon3 allele, OR(epsilon4), were not equal in all age classes: OR(epsilon4) in the extreme groups with onset at < 60 years or > 79 years were significantly lower than those from the age groups 60-79 years. In epsilon3/epsilon4 individuals, sex-specific lifetime risk estimates by age 85 years (i.e., sex-specific penetrances by age 85 years) were 0.14 (95% CI 0.04-0.30) for men and 0.17 (95% CI 0.09-0.28) for women.

Evidence for major gene inheritance of Alzheimer disease in families of patients with and without apolipoprotein E epsilon 4

Apolipoprotein E (APOE) genotype is the single most important determinant to the common form of Alzheimer disease (AD) yet identified. Several studies show that family history of AD is not entirely accounted for by APOE genotype. Also, there is evidence for an interaction between APOE genotype and gender. We carried out a complex segregation analysis in 636 nuclear families of consecutively ascertained and rigorously diagnosed probands in the Multi-Institutional Research in Alzheimer Genetic Epidemiology study in order to derive models of disease transmission which account for the influences of APOE genotype of the proband and gender. In the total group of families, models postulating sporadic occurrence, no major gene effect, random environmental transmission, and Mendelian inheritance were rejected. Transmission of AD in families of probands with at least one epsilon 4 allele best fit a dominant model. Moreover, single gene inheritance best explained clustering of the disorder in families of probands lacking epsilon 4, but a more complex genetic model or multiple genetic models may ultimately account for risk in this group of families. Our results also suggest that susceptibility to AD differs between men and women regardless of the proband's APOE status. Assuming a dominant model, AD appears to be completely penetrant in women, whereas only 62%-65% of men with predisposing genotypes develop AD. However, parameter estimates from the arbitrary major gene model suggests that AD is expressed dominantly in women and additively in men. These observations, taken together with epidemiologic data, are consistent with the hypothesis of an interaction between genes and other biological factors affecting disease susceptibility.

Expression of apolipoprotein E inhibits aggregation of the C-terminal fragments of beta-amyloid precursor protein

An important role of apolipoprotein E in the amyloidogenesis of Alzheimer's disease is suggested by an accumulation of apolipoprotein E in beta-amyloid plaques and a genetic association between Alzheimer's disease and one of the allelic variants (APOE4) of apolipoprotein E. Overexpression of a C-terminal region of beta-amyloid precursor protein brings about aggregation of the C-terminal fragments in COS cells. This COS cell culture system was used to study effects of apolipoprotein E on aggregation of the C-terminal fragments. When both apolipoprotein E and the C-terminal fragments were overexpressed in COS cells, Western blot analyses revealed significant inhibition of aggregation of the C-terminal fragments. No significant differences between apolipoprotein E3 and E4 in the inhibitory activities were found by this method. Apolipoprotein E may inhibit formation of amyloid fibrils.