Apolipoprotein E: a review of its roles in lipoprotein metabolism, neuronal growth and repair and as a risk factor for Alzheimer's disease

Core Matrisome Protein Signature During Periodontal Ligament Maturation From Pre-occlusal Eruption to Occlusal Function

The pre-occlusal eruption brings the molars into functional occlusion and initiates tensional strains during mastication. We hypothesized that upon establishment of occlusal contact, the periodontal ligament (PDL) undergoes cell and extracellular matrix maturation to adapt to this mechanical function. The PDL of 12 Wistar male rats were laser microdissected to observe the proteomic changes between stages of pre-occlusal eruption, initial occlusal contact and 1-week after occlusion. The proteome was screened by mass spectrometry and confirmed by immunofluorescence. The PDL underwent maturation upon establishment of occlusion. Downregulation of alpha-fetoprotein stem cell marker and protein synthesis markers indicate cell differentiation. Upregulated proteins were components of the extracellular matrix (ECM) and were characterized with the matrisome project database. In particular, periostin, a major protein of the PDL, was induced following occlusal contact and localized around collagen α-1 (III) bundles. This co-localization coincided with organization of collagen fibers in direction of the occlusal forces. Establishment of occlusion coincides with cellular differentiation and the maturation of the PDL. Co-localization of periostin and collagen with subsequent fiber organization may help counteract tensional forces and reinforce the ECM structure. This may be a key mechanism of the PDL to adapt to occlusal forces and maintain structural integrity.

Association between apolipoprotein E genotypes and panic disorder in Turkish population

AIM

In this study, we aimed to investigate possible interactions among the apolipoprotein E (ApoE) and panic disorder (PD), taking into account serum cholesterol levels and subfractions.

METHODS

ApoE genotyping was performed by real-time polymerase chain reaction in DNA samples of PD patient group (n = 45) and healthy control group (n = 50). The serum lipid levels, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) subfraction analysis were examined.

RESULTS

There was a significant difference of ApoE genotypes in patient and control groups. The E3/E3 genotypes lower whereas E4 allele carriers were significantly higher in PD group ApoE4allele carriers had 3.2-fold higher risk of PD. PD group had significantly lower LDL and HDL levels. In spite of the decreased levels of total LDL, antiatherogenic large LDL subgroup was significantly lower in a patient with PD. Antiatherogenic large HDL and Intermediate HDL levels were lower, while atherogenic small HDL subfraction was significantly higher in PD group. Furthermore, Apo E3/E3 genotype carriers had significantly higher large LDL, HDL, large HDL, intermediate HDL level, and also had highest HDL between all the groups. ApoE4 allele carriers while they had highest atherogenic small HDL level.

CONCLUSION

E4 allele can be associated with PD as an eligible risk factor, the E3/E3 could be a risk-reducing factor for PD. Patients with PD not only had lower LDL and HDL levels but also they have higher atherogenic LDL and HDL subfractions. Also, E3/E3 genotype carriers had convenient but ApoE4 carriers had atherogenic plasma cholesterol levels and subfractions.

ACE polymorphism and use of ACE inhibitors: effects on memory performance

Memory is an important cognition function, being fundamental to the development and independence of individuals. Our aim was to investigate the influence apolipoprotein E (APOE) and angiotensin I-converting enzyme (ACE) polymorphism and ACE inhibitors use, besides their interaction on memory performance of healthy subjects over 50 years. The sample consisted of 205 subjects assessed for five types of episodic memory, using Wechsler Memory Scale-Revised (WMS-R), who answered a questionnaire about drug use and were assessed for the ACE insertion/deletion polymorphism and APOE polymorphism. We found no influence of the APOE gene. The use of ACE inhibitors beneficially influenced learning ability scores (p = 0.02). Besides, I allele carriers of ACE polymorphism showed higher verbal memory scores compared with homozygous DD. Also, we observed an interaction influencing learning ability between the ACE polymorphism and the use of inhibitors, the beneficial influence of the I allele was present only in individuals who make use of ACE inhibitors. We conclude that the ACE gene has influence on memory performance, and that this influence is modulated by ACE inhibitors use.

Genetic animal models of cerebral vasculopathies

Cerebral amyloid angiopathy (CAA) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) are genetic cerebrovasculopathies associated with neurodegeneration and vascular cognitive impairment. Linked to autosomal dominant mutations in diverse genes that encode cell-surface receptors (i.e., amyloid precursor protein in CAA and NOTCH3 in CADASIL), both diseases are associated with accumulation of abnormal material around cerebral vessels, such as amyloid in CAA or granular osmiophilic material in CADASIL. Both CAA and CADASIL share clinical features of white matter degeneration and infarcts, and vascular dementia in the human adult; microbleeds occur in both CADASIL and CAA, but large intracerebral hemorrhages are more characteristic for the latter. While the mechanisms are poorly understood, wall thickening, luminal narrowing, and eventual loss of vascular smooth muscle cells are overlapping pathologies involving leptomeningeal, and pial or penetrating small arteries and arterioles in CAA and CADASIL. Dysregulation of cerebral blood flow and eventual hypoperfusion are believed to be the key pathophysiological steps in neurodegeneration and cognitive impairment. Although animal models expressing CAA or CADASIL mutations have partially reproduced the human pathology, there has been marked heterogeneity in the phenotypic spectrum, possibly due to genetic background differences among mouse models, and obvious species differences between mouse and man. Here, we provide an overview of animal models of CAA and CADASIL and the insight on molecular and physiological mechanisms of disease gained from these models.

A polymorphism of apolipoprotein E (APOE) gene is associated with age at natural menopause in Caucasian females

OBJECTIVE

The present study aimed to investigate possible association of the apolipoprotein E (APOE) gene polymorphisms with age at natural menopause (ANM) in Caucasian females.

DESIGN

Four SNPs (including two replacements, SNP3 Cys112Arg and SNP4 Arg158Cys) were genotyped in 253 randomly selected unrelated Caucasian women having experienced natural menopause. The comprehensive statistical analyses focusing on the association of the APOE gene and some environmental factors with ANM were conducted.

RESULTS

Alcohol consumption was a significantly predictor of earlier natural menopause (P<0.05). One SNP (rs769450) was significantly associated with ANM according to both population based and the transmission disequilibrium test (TDT) analyses (P=0.007 and 0.046, respectively). However, no association was observed between APOE varepsilon2, varepsilon3, varepsilon4 and ANM.

CONCLUSIONS

Genetic variation in the APOE gene may influence the variation in ANM in Caucasian women.

Associations of apolipoprotein E polymorphism with low-density lipoprotein size and subfraction profiles in Arab patients with coronary heart disease

The APOE gene locus has 3 major alleles, E3, E4 and E2, which variably influence coronary heart disease (CHD) risk. Plasma low-density lipoprotein (LDL) profile, another major CHD risk factor, is characterized on the basis of size and density into 2 main patterns: large buoyant LDL and small dense LDL. The latter has also been linked with increased CHD risk. This study investigates associations of specific APOE allelic patterns with LDL size and subfraction profiles in patients with CHD and healthy control subjects. We recruited 2 groups of male subjects: (A) 65 apparently healthy control subjects, median age, 39.0 years (range, 25.0-60.0 years); (B) 50 patients with CHD, median age, 54.0 years (range, 40.0-76.0 years). APOE genotypes were determined by validated polymerase chain reaction-restriction fragment length polymorphism methods, and LDL size and subfractions were assessed by a high-resolution, nongradient polyacrylamide gel electrophoresis technique (LIPOPRINT, Quantimetrix, Redondo Beach, CA). Lipid and other biochemical analyses were done by autoanalyzer techniques. The associations of specific APOE alleles and genotypes with LDL size and subfraction patterns were then assessed. As expected, patients with CHD had a worse atherogenic lipoprotein profile (waist-hip ratio, LDL, uric acid, and apolipoprotein B) than the controls. APOE genotype and allele frequencies were similar for both groups. In either group, median percent large buoyant LDL (pattern A) was greater in controls (51.0% vs 46.5%, P<.001) and percent small dense LDL (pattern B) was greater with CHD (9.0% vs 3.0%, P<.001). The latter also had smaller median particle size (26.5 vs 26.9 nm, P<.001). In controls, percent LDL pattern B was significantly lower with APOE2 than with APO non-E2 (4.0% vs 0.0%, P<.05); in patients with CHD, E2 patients had smaller particle size, and pattern B was significantly lower with non-E2 than with E2 (15.0 vs 8.0, P<.05). With respect to E4, control non-E4 had a smaller median percent LDL pattern B than E4; otherwise, there were no significant findings in relation to APOE type and LDL size and subfractions in both subject groups. These results confirm observations in other populations of increased levels of small dense LDL in patients with CHD. Although the APOE allelic pattern, especially APOE2, could be related to LDL subfraction profiles in control subjects, such associations could not be demonstrated in those with CHD.

Association between apolipoprotein E polymorphism and serum lipid and apolipoprotein levels with Alzheimer's disease

We have recently demonstrated that apolipoprotein E (APOE)-varepsilon4 allele is a risk factor for Alzheimer disease (AD) in Tehran, Iran. The current study specifically aimed to examine whether APOE polymorphism in association with serum lipids-apolipoprotein level is a risk factor for AD in a population from Tehran, Iran. APOE polymorphism and plasma lipids, apoA1, apoB and lipoprotein (a) (Lp(a)) levels were determined in 94 AD patients and 111matched controls. Our study demonstrated a significant association between APOE polymorphism and the level of plasma lipids and apolipoprotein with AD in this population. The AD subjects had significantly lower apoA1 (p<0.001) and HDL-C (p<0.01) and higher apoB (p=0.01) and LDL-C (p=0.02) levels than that of the control group. The AD subjects carrying APOE-varepsilon4 allele had lower plasma apoA1 (t=5.2, p<0.002) and HDL-C level (t=2.7, p=0.01) but had higher plasma apoB (t=-5.4, p<0.002), LDL-C (t=-4.6, p=0.005) and total cholesterol (TC) (t=-2.7, p=0.01) than that of the non APOE-varepsilon4 carriers. These results indicated that AD patients with APOE-varepsilon4 allele has a distinct plasma lipid profile and carrier of this allele with low levels of apoA1 and HDL-C may be more susceptible to AD.

The effect of apolipoprotein E genotype on serum lipoprotein particle response to exercise

Exercise affects lipoprotein metabolism and apolipoprotein E (Apo E) genotype may alter changes in lipoprotein subclasses that occur with exercise. The present study examined the effects of Apo E genotype (APOE) on the response of lipoprotein subclass concentrations to long-term exercise. A prospective longitudinal study, conducted at seven centers, genetically screened 566 individuals to create three cohorts of healthy adults, equal for gender and the most common APOE variants: E2/3 (n = 35), E3/3 (n = 40), and E3/4 (n = 31). Subjects with body mass index (BMI) > or = 31 or evidence of dyslipidemia or metabolic disease were excluded. All subjects exercised aerobically at 75% of maximal heart rate for 40 min, four times weekly for 6 months. Fasting lipoprotein subpopulations were measured before and after exercise training using proton nuclear magnetic resonance spectroscopy. Serum lipids for the entire cohort did not change with exercise training, but the LDL subpopulation response varied by APOE. Small-sized LDL particles decreased only in the APOE3 homozygotes whereas medium-sized LDL particles increased only in this group. These changes were directionally different from the responses in the E2/3 and E3/4 subjects (p < 0.05). Neither exercise nor APOE variant affected overall LDL or HDL size or cholesterol concentration, but exercise decreased VLDL diameter by 3.5 nm (p < 0.001) attributable to decreases in large VLDL in each APOE group. In conclusion, APOE variants influence the serum LDL subpopulation response to exercise training in normolipidemic subjects. Subjects homozygous for APOE3 experienced the most beneficial lipid effects from exercise training.

Social Environments and the Genetics of Aging: Advancing Knowledge of Protective Health Mechanisms

We selectively review the literature in behavioral and molecular genetics, including both laboratory and epidemiologic studies, with emphasis on how social environments, particularly emotion in significant social relationships, influence gene expression. Attention is given to cross-talk between human and animal studies. Environments are pivotal in understanding phenotypic outcomes, and this demands research on gene-environment interactions. Illustrative interactions, involving both behavioral and molecular genetics, are provided. Many people with susceptibility genes for diverse diseases never proceed to disease status. Substantial associational evidence implicates social environmental factors as protective agents. Mechanistic understanding of these linkages is quite advanced in some animal populations and suggests new lines of inquiry in human studies. Developing the interface between genetics, social environments, and health will require close collaboration between those well versed in molecular biology and biochemistry and persons with expertise in genetic epidemiology and social psychology. Particularly important is the identification of environmental influences that protect susceptible persons from disease incidence.

Gene-environment interplay in relation to emotional and behavioral disturbance

The conceptual and methodological issues involved in the study of gene-environment correlations (rGE) and interactions (GxE) are discussed in historical context. Quantitative genetic findings are considered with respect to rGE and GxE in relation to emotional and behavioral disturbance. Key conceptual and substantive implications are outlined in relation to both genetic and environmental risk mediation, with a brief note on evolutionary considerations.

Potential genetic markers of sporadic Alzheimer's dementia

Polymorphisms within the genes encoding apolipoprotein E (ApoE), apolipoprotein CI (ApoCI), alpha1-antichymotrypsin (ACT), the low-density lipoprotein (LDL) receptor and lipoprotein lipase were investigated in patients suffering from Alzheimer's dementia and non-demented psychiatric patients as control subjects. The ApoE allele 4, well known as a risk factor in Alzheimer's disease, and the ApoCI allele A2, which is closely linked to the ApoE allele 4, were found elevated in the index group. Concerning the polymorphism within exon 8 of the LDL receptor (alanin/threonin), there was also a predominance of the allele carrying threonin in the index group, which barely missed significance. Distribution of the polymorphisms of ACT and lipoprotein lipase were similar in both groups investigated. We conclude that, apart from the ApoE allele 4, other genetically regulated factors like ApoCI and the LDL receptor modulate the individual risk for Alzheimer's disease.

Cognitive effects of insulin in the central nervous system

Evidence has been accumulating recently that the hormone insulin may modulate cognitive activity by acting in the central nervous system. Initially derived from the observation that insulin and insulin receptors are found in specific brain areas, this evidence also includes cognitive assessments of humans in insulin-deficient and insulin-resistant disease states and experimental manipulation of rodent models. Additional support is derived from in vivo and in vitro systems that are used to investigate the neurophysiological basis of learning and memory. This article is a brief review of the literature that suggests a connection between insulin and memory and draws together some of the findings relevant to possible physiological mechanisms for this cognitive effect.

A healthy body, a healthy mind: long-term impact of diet on mood and cognitive function

Certain dietary risk factors for physical ill health are also risk factors for depression and cognitive impairment. Although cholesterol lowering has been suggested to increase vulnerability to depression, there is better support for an alternative hypothesis that intake of n-3 long-chain polyunsaturated fatty acids can affect mood (and aggression). Possible mechanisms for such effects include modification of neuronal cell membrane fluidity and consequent impact on neurotransmitter function. Stronger evidence exists concerning a role for diet in influencing cognitive impairment and cognitive decline in older age, in particular through its impact on vascular disease. For example, cognitive impairment is associated with atherosclerosis, type 2 diabetes and hypertension, and findings from a broad range of studies show significant relationships between cognitive function and intakes of various nutrients, including long-chain polyunsaturated fatty acids, antioxidant vitamins, and folate and vitamin B12. Further support is provided by data on nutrient status and cognitive function. Almost all this evidence, however, comes from epidemiological and correlational studies. Given the problem of separating cause and effect from such evidence, and the fact that cognitive impairment and cognitive decline (and depression) are very likely to be significant factors contributing to the consumption of a poor diet, greater emphasis should now be placed on conducting intervention studies. An efficient approach to this problem could be to include assessments of mood and cognitive function as outcome measures in studies designed primarily to investigate the impact of dietary interventions on markers of physical health.

Association of apolipoprotein E polymorphism with plasma lipids and Alzheimer's disease in a Southern Brazilian population

Apolipoprotein E (protein: apo E; gene: APOE) plays an important role in the multifactorial etiology of both Alzheimer's disease (AD) and lipid level concentrations. The polymerase chain reaction (PCR) was used to investigate the APOE gene polymorphism in 446 unrelated Caucasians, among them 23 AD patients, and 100 Afro-Brazilians living in Porto Alegre, Brazil. The frequencies of the APOE*2, APOE*3 and APOE*4 alleles were 0.075, 0.810 and 0.115 in Caucasians and 0.075, 0.700 and 0.225 in Afro-Brazilians, respectively (chi2 = 8.72, P = 0.013). A highly significant association was observed between the APOE*4 allele and AD in this population-based sample. The APOE*4 frequency in AD patients (39%) was about four times higher than in the general Caucasian population (11.5%). The influence of each of the three common APOE alleles on lipid traits was evaluated by the use of the average excess statistic. The E*2 allele is associated with lower levels of triglycerides and of total and non-HDL cholesterol in both men and women. Conversely, the E*4 allele is associated with higher levels of these traits in women only. The effect of APOE alleles was of greater magnitude in women.

Ageing and learning disability

BACKGROUND

Ageing is a continuation of the developmental process and is influenced by genetic and other biological factors as well as personal and social circumstances.

AIMS

To identify some key biological, psychological and social issues relevant to how ageing might particularly effect people with learning disabilities.

METHOD

This selected review considers the extent to which there are similarities and differences relative to people without learning disabilities.

RESULTS

There is a convergence, in later life, between people with a learning disability and those without, owing to the reduced life expectancy of people with more severe disabilities. People with Down's syndrome have particular risks of age-related problems relatively early in life.

CONCLUSIONS

The improved life expectancy of people with learning disabilities is well established. There is a lack of a concerted response to ensure that the best possible health and social care is provided for people with learning disabilities in later life.

Desialylation of human apolipoprotein E decreases its binding to human high-density lipoprotein and its ability to deliver esterified cholesterol to the liver

Apolipoprotein E (apoE) plays a significant role in the delivery of high-density lipoprotein (HDL) cholesterol to the liver via the apoB/E receptor. The roles of the apoE sialylation status in its association with HDL and in the reverse cholesterol transport (RCT) function of HDL have not been well defined. Furthermore, long-term ethanol treatment impairs apoE sialylation and leads to its decreased content in HDL. Therefore, we investigated the association of either sialo apoE (SapoE) or desialo apoE (DSapoE) with HDL and its effect on the RCT function of HDL. The dextran sulfate precipitation method showed that [125I]DSapoE binding to HDL was 27.3% (P < .02) to 35.5% (P < .001) lower versus [125I]SapoE. Scatchard analysis of the specific binding data showed that [125I]SapoE had 11.2 times more affinity for HDL than [125I]DSapoE based on size-exclusion chromatography (Kd = 89.7 v 1,010 nmol/L). Similarly, [1251]HDL had 4.5 times more affinity for SapoE compared with DSapoE based on solid-phase binding (Kd = 21.9 v 104.4 nmol/L). Furthermore, esterified cholesterol uptake from reconstituted HDL particles (rHDLs) by HepG2 cells increased over basal uptake up to 153% when rHDLs contained SapoE, versus only 37% with DSapoE. Enzymatic resialylation of DSapoE completely restored its HDL-binding and RCT properties, identical to those of SapoE. It is therefore concluded that desialylation of apoE decreases its binding to plasma HDL, leading to an impaired RCT function.

The influence of coincidental vascular pathology on symptomatology and course of Alzheimer's disease

The aim of this review is to determine the influence of coincidental cerebrovascular pathology on the symptomatology and course of Alzheimer's disease (AD). The link between stroke and AD is probably higher than expected by chance for the following reasons: (i) both pathologies share genetic risk factors such as the epsilon 4 allele of the apolipoprotein E gene; (ii) AD patients have changes in the brain vessels that may lead to either ischemic or hemorrhagic stroke or white matter changes or both; (iii) there is evidence of an increased risk of stroke in AD patients; (iv) there is evidence of a frequent association of AD and stroke at autopsy. Because of the summation of the various types of lesions, stroke lesions may lead to an increase progression of cognitive decline in AD patients. Recognition of a vascular component in a dementia syndrome is therefore useful for the management of AD patients. Whether an optimal management of risk factors for stroke may delay the clinical expression of dementia in patients with preclinical Alzheimer pathology should be evaluated.

Alpha-1-antichymotrypsin bi-allele polymorphism, apolipoprotein-E tri-allele polymorphism and genetic risk of Alzheimer's syndrome

The alpha1-antichymotrypsin and apolipoprotein-E polymorphisms were investigated in patients suffering from Alzheimer's syndrome and non-demented psychiatric inpatients as controls. The apolipoprotein E allele 4, well known as risk factor, tended to be elevated in the index group. The frequency of the alpha1-antichymotrypsin allele A was significantly increased in patients with Alzheimer's syndrome: 0.647 vs. 0.483 (chi-square test, p < 0.05). We conclude that, apart from the apolipoprotein E allele 4, the alpha1-antichymotrypsin allele A possibly represents a second genetic factor increasing individual's risk for Alzheimer's syndrome.

Elevation of apolipoprotein E in the CSF of cattle affected by BSE

The cerebrospinal fluid (CSF) of patients suffering from Creutzfeldt-Jakob disease (CJD) display two unique polypeptide chains by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). In the absence of a well-defined ante-mortem diagnostic test for bovine spongiform encephalopathy (BSE), spinal fluid samples of eight normal cows and eight cows known to carry BSE by post-mortem histological analysis were investigated to verify if equivalent polypeptides were present. Proteins with similar migration to human CJD polypeptides were not detected. But surprisingly, a cluster of polypeptide spots that was faint or not detected in normal bovine CSF samples was found to be elevated or massively increased in BSE CSF samples (more than 10-fold increase). These elevated polypeptide chains were identified as apolipoprotein E.

Alzheimer's disease: risk and protection

Only four risk factors for Alzheimer's disease can be regarded as confirmed--old age, family history of dementia, apo-E genotype and Down syndrome. Other disputed risk factors with some supporting evidence include ethnic group, head trauma and aluminium in drinking water. Possible protection factors, such as anti-inflammatory drugs, oestrogen replacement therapy and a high education level, are of great interest because they suggest possible preventive action.

The genetics of Alzheimer's disease

Alzheimer's disease (AD) is the major cause of dementia in the U.K. The clinical diagnosis of the specific disease resulting in dementia is unreliable and thus a definitive diagnosis of AD is best made in conjunction with post-mortem findings of amyloid plaques and neurofibrillary tangles. Alzheimer's disease is neuropathologically indistinguishable in the young and old, but has been divided arbitrarily into early- and late-onset disease using age cut-offs of 60 or 65 years. Twin and family studies suggest that genetic factors play a major role in its aetiology. This review considers the three loci which have been shown to be associated with early-onset AD: amyloid precursor protein, presenilin (PS)-1 and PS-2. Mutations in these genes seem to be associated with overproduction of the 42-amino acid form of beta-amyloid, suggesting that this may be a central pathological process in AD. The impact of the different apo E alleles on the risks for late- and early-onset AD is discussed and compared with other dementing conditions. Recent analyses suggest that there are likely to be other genes besides apo E which impact on late-onset AD risk. The possible roles in AD of the mitochondrial mutation at position 4336, the PS intron 8 polymorphism, and variants in the alpha 1-antichymotrypsin and VLDL-receptor genes, are considered.

Implications of genetic research for child psychiatry

OBJECTIVE

To review implications of genetic research in child psychiatry.

METHOD

Key advances in quantitative and molecular genetics are noted and findings are summarized with respect to autism, attention-deficit hyperactivity disorder, oppositional defiant and conduct disorders, depression, schizophrenia, and Tourette's syndrome.

CONCLUSIONS

Genetic findings will be helpful clinically in the elucidation of disordered brain processes, the understanding of nature-nurture interplay, diagnosis, genetic counselling, and pharmacotherapy.

Analysis of alpha-1 antichymotrypsin, presenilin-1, angiotensin-converting enzyme, and methylenetetrahydrofolate reductase loci as candidates for dementia

The genetic factors which predispose individuals to dementia in old age have not been fully defined. Although the apolipoprotein E4 allele accounts for a proportion of the genetic risk for late-onset Alzheimer disease (AD), it is neither necessary nor sufficient to cause this disease. Recent suggestions that other loci are involved in dementia risk have been supported by findings of associations of genotypes at the alpha-1 antichymotrypsin (ACT) and presenilin-1 (PS-1) loci with AD. We investigated these loci in two community-based aged Cambridgeshire populations: the rural Ely population (cohort 1) comprised 60 pairs of demented and nondemented elderly individuals, with a mean age of 84.2 years; and the Cambridge city population (cohort 2) comprised 81 pairs all over age 84, with a mean age of 87.3 years. Since vascular risk factors are likely to impact on dementia risk, we also examined the angiotensin-converting enzyme (ACE) and methylenetetrahydrofolate reductase (MTHFR) genes as candidates. ACE, ACT, PS-1, and MTHFR genotype and allele frequencies were not significantly different in cases and matched controls. These data support the doubts which have been raised about the involvement of the PS-1 and ACT polymorphisms in late-onset dementia.

Analysis of the apo E/apo C-I, angiotensin converting enzyme and methylenetetrahydrofolate reductase genes as candidates affecting human longevity

Genetic factors are likely to affect human survival, since twin studies have shown greater concordance for age of death in monozygotic compared to dizygotic twins. Coronary artery disease is an important contributor to premature mortality in the UK. Accordingly, we have chosen genes associated with cardiovascular risk, apo E/apo C-I, angiotensin converting enzyme (ACE) and methylenetetrahydrofolate reductase (MTHFR), as candidates which may affect longevity/survival into old age. An association study was performed by comparing allele and genotype frequencies at polymorphic loci associated with these genes in 182 women and 100 men aged 84 years and older with 100 boys and 100 girls younger than 17 years. MTHFR allele and genotype frequencies were similar in the elderly and young populations. Apo C-I allele and genotype frequencies were significantly different in the elderly women compared to the younger sample (P < 0.05). No difference was observed in the elderly men. At the neighbouring apo E gene, we only observed a difference between genotypes in the elderly women and the young sample; however, this did not retain significance when the genotype frequencies of the young sample were adjusted to values expected from the allele frequencies on the basis of Hardy-Weinberg equilibrium and compared to observed genotypes in elderly men and women. In contrast to previous studies, apo E2 was not overrepresented in the elderly men or women. Thus, the proposition that apo E2, E3 and E4 protein isoforms are themselves functionally associated with increasing risks for early death, may be too simplistic. The I/I ACE was depleted in the elderly males but not the elderly females. Furthermore, significant differences were observed between ACE genotypes in elderly men and elderly women. These data suggest that the penetrance of loci which influence survival may vary according to sex. The depletion of the ACE I/I genotype in elderly men is generally consistent with a previous study which found decreased frequencies of the I allele in French centenarians compared to younger controls. However, these results are apparently paradoxical, since others have suggested that the I allele is associated with increased cardiovascular risk. Clarification of the overall effect of a genotype on survival will be vital if therapies are to be considered which target specific genetic variants.

The tRNA(Gln) 4336 mitochondrial DNA variant is not a high penetrance mutation which predisposes to dementia before the age of 75 years

The genetic factors that predispose to Alzheimer's disease (AD) are heterogeneous. Two recent reports have suggested that a mitochondrial DNA mutation within the tRNAGln gene, located at position 4336, may be a risk factor for AD, as it was found in 10/256 (3.9%) cases with AD confirmed by necropsy. Although low prevalences of this mutation were detected in non-demented subjects in both of these studies, the controls were not carefully matched with the AD cases. We have investigated the frequency of this mutation in two community based elderly cohorts in Cambridgeshire, who have participated in longitudinal studies of cognitive function. The 4336 mitochondrial mutation was detected in 8/ 443 people examined. These people were found to be non-demented at ages 74, 81, 84, 86, 89, 90, 91, and 102 years, in contrast to the previously described cases whose onset of dementia occurred between 60 and 76 years (mean 68). Accordingly, we believe that this mitochondrial variant is not a high penetrance mutation which predisposes to dementia before the age of 76 years.