Apolipoprotein-E genotype in normal aging, age-associated memory impairment, Alzheimer's disease and vascular dementia patients

Age-associated memory impairment and related disorders

Complaints of poor memory are common in the healthy elderly and to many it may seem unsurprising that cognitive function declines with ‘normal’ ageing. Virtually every biological system alters with age and, just as a 70-year-old cannot run as fast or hear as well as when he or she was 20, it is perhaps inevitable that cognitive function also becomes impaired. However, far from being straightforward, the nature, classification and clinical significance of age-related cognitive changes that fall short of dementia remain a most controversial and difficult area (see O'Brien & Beats, 1994; Dal Forno & Kawas, 1995). The recent emergence of new drugs for the treatment of Alzheimer's disease (donepezil and rivastigmine) and related disorders has emphasised the need to study groups with milder degrees of cognitive impairment. It is necessary to determine whether such conditions are benign and non-progressive, or harbingers of progressive dementia and so appropriate conditions to target for early therapeutic intervention. The presence of age-related cognitive changes raises other important issues including why such changes occur, how they should be classified and whether, even if ‘benign’, they can and should be treated.

Association between dementia and vascular disease-associated polymorphisms in a Tunisian population

PURPOSE

Dementia is a multifactorial idiopathic pathology caused by clinical, eDementia is a multifactorial idiopathic pathology caused by clinical, environmental and genetic factors. Hence, its etiology is still unknown. We aimed to evaluate the association between five genetic risk factors for vascular diseases and dementia individually and when gathered in haplotypes.

MATERIALS AND METHOD

We enrolled 200 dementia patients and 300 controls. All subjects were genotyped for vascular diseaseassociated polymorphisms in the genes coding for Apolipoprotein-E (ApoE), angiotensin converting enzyme (ACE) and Paraoxonase-1 (PON1).

RESULTS

The association between dementia risk and all the studied polymorphisms except of PON1-Q192R was found to be significant. Carrying the ApoE e4 allele seems to increase dementia risk by 4.32 fold (p = 0.001). The risk associated with ACE I and PON1-L55M T alleles were lower (2.58 and 2.11 fold, p < 0.001 and p = 0.015, respectively). When combined in haplotypes, these polymorphisms showed a cumulative and synergetic effect. GTICC haplotype appears to be associated with 9-fold dementia risk (p < 0.001), whereas AADTT seems to reduce dementia risk by 80% (p = 0.003).

CONCLUSION

Our results suggest that, ApoE ε4, ACE I and PON1-L55M T alleles are associated with dementia risk whether these polymorphisms were studied separately or gathered in haplotypes. Still, the contribution of each gene to the pathophysiological development of dementia must be more investigated.

Lack of association between apolipoprotein E polymorphism and vascular dementia in Koreans

To investigate an association of vascular dementia (VD) with the apolipoprotein E (APOE) polymorphism, the APOE polymorphism of 100 VD patients, 100 age- and gender-matched Alzheimer disease (AD) patients, and 200 age- and gender-matched nondemented control (NC) subjects was genotyped. The distribution of APOE polymorphism was compared. Neither the APOE epsilon4 allele nor the APOE epsilon2 allele was more prevalent in the VD patients compared with the NC subjects (P > .1 by the chi 2 test), which was the case when both men and women were analyzed separately (P > .1 by the chi2 test) and when young patients (75 years old or less) and old patients (more than 75 years old) were analyzed separately (P > .1 by the chi2 test). The estimated statistical power was over 0.80 when the odds ratios (OR) for VD conferred to the APOE epsilon4 are assumed to be higher than 2.2 and the type I error probability is set at 0.05, which is much higher than the power of the previous studies on the VD/APOE association. In conclusion, the results suggested that APOE epsilon4 allele does not confer the risk for VD, and even if it does, it does so very modestly.

Variation at APOE and STH loci and Alzheimer's disease

Background

The apolipoprotein E (APOE) and tau proteins play important roles in the pathological development of Alzheimer's disease (AD). Many studies have shown an association between the APOE gene and AD. Association between AD and the newly discovered saitohin (STH) gene, nested within the intron of the tau gene, has been reported. The present study aimed to elucidate the association between APOE and AD, and between STH and AD in our sample.

Methods

The functional polymorphisms, rs429358 and rs7412, in the APOE gene (which together define the ε2, ε3, and ε4 alleles), and the Q7R SNP in the STH gene, were genotyped in 369 patients with AD and 289 healthy European-Americans. The associations between these two genes and AD were analyzed in a case-control design.

Results

Consistent with previously reported results, the frequencies of the APOE ε4 allele, ε4/ε4 genotype and ε3/ε4 genotype were significantly higher in AD cases than controls; the ε4/ε4 genotype frequency was significantly higher in early-onset AD (EOAD) than late-onset AD (LOAD); the frequencies of the ε2 allele, ε3 allele, ε3/ε3 genotype and ε2/ε3 genotype were significantly lower in AD cases than controls. Positive likelihood ratios (LRs⁺) of APOE alleles and genotypes increased in a linear trend with the number of ε4 alleles and decreased in a linear trend with the number of ε2 or ε3 alleles. There was no significant difference in the STH allele and genotype frequency distributions between AD cases and controls.

Conclusion

This study confirmed that the ε4 allele is a dose-response risk factor for AD and the ε4/ε4 genotype was associated with a significantly earlier age of onset. Moreover, we found that the ε2 allele was a dose-response protective factor for AD and the ε3 allele exerted a weaker dose-response protective effect for risk of AD compared with ε2. In a clinical setting, APOE genotyping could offer additional biological evidence of whether a subject may develop AD, but it is not robust enough to serve as an independent screening or predictive test in the diagnosis of AD. STH variation was not significantly associated with AD in our sample.

Apolipoprotein E epsilon4 genotype as a risk factor for cognitive decline and dementia: data from the Canadian Study of Health and Aging

BACKGROUND

Apolipoprotein E (ApoE) epsilon4 genotype is a well-established risk factor for Alzheimer's disease (AD). However, its effect on predicting conversion from normal to "cognitive impairment, no dementia" (CIND) and from CIND to AD is less clear.

METHODS

We used a nested case-control design from the population-based Canadian Study of Health and Aging (CSHA) to examine the effect of ApoE epsilon4 genotype on the conversion of subjects from normal to CIND and from CIND to AD. We also contrasted these findings with incident cases of AD and vascular dementia (VaD) in the CSHA cohort.

RESULTS

The ApoE epsilon4 genotype was a significant risk factor for conversion from CIND to AD and from normal to AD and VaD. However, it was not a significant risk factor for conversion from normal to CIND. This effect is robust to adjustment for age, sex and education level. There is significant interaction between the ApoE epsilon4 genotype and age for AD and for conversion from CIND to AD. No interaction between ApoE epsilon4 genotype, sex, age, ethnicity and education level was found in other subgroup analyses. The positive predictive value of ApoE epsilon4 for predicting CIND conversion to AD was 0.48, and the negative predictive value was 0.65.

INTERPRETATION

Possession of an ApoE epsilon4 allele increases the risk of AD developing from CIND. It is also associated with a decrease in the age at onset of AD. Its predictive values do not support its utility as a diagnostic test for predicting progression from CIND to AD, but it may be useful in research studies to enrich study samples that have a higher rate of progression to AD.

Apolipoprotein E polymorphism and cognitive impairment in a bi-ethnic community-dwelling elderly sample

The epsilon 4 (epsilon 4) and epsilon 2 (epsilon 2) alleles of the apolipoprotein gene (APOE) located on chromosome 19 have been associated with increased and decreased risk for Alzheimer disease (AD) in older adults, respectively. However, there is a dearth of studies examining the relation of APOE polymorphism with cognitive functioning among community-dwelling ethnic minority elderly. This study examined the risk for cognitive impairment associated with the APOE epsilon 4 and epsilon 2 alleles in a community-based cohort of non-Hispanic white (NHW; N = 739) and white Hispanics (WH; N=321). All patients were recruited consecutively from a memory-screening program and evaluated using standardized assessment procedures. Cognitive impairment was classified according to an age and education adjusted Folstein Mini-Mental State Exam (MMSAdj) score of less than 24. The results indicated the APOE epsilon 4 allele was associated with increased risk for cognitive dysfunction in NHW and WH after controlling for the effects of age, education, and gender. This risk was generally observed to be dose-dependent, with greater risk among epsilon 4 homozygotes in relation to epsilon 4 heterozygotes. The epsilon 2 allele of APOE did not confer decreased risk for cognitive impairment among NHW and WH. This study supports the relation of APOE polymorphism to cognitive dysfunction among two ethnic populations residing in the community.

Neuropsychological and genetic differences between age-associated memory impairment and mild cognitive impairment entities

OBJECTIVE

To neuropsychologically and genetically compare age-associated memory impairment (AAMI) and mild cognitive impairment (MCI) entities and to determine what proportion of AAMI diagnosed individuals could also receive a MCI diagnosis. To compare the distribution of a previously known genetic risk factor for Alzheimer's disease (apolipoprotein E common polymorphism) associated with these two conditions with a sample of the normal aging.

DESIGN

Neuropsychological and genetic assessments in AAMI and MCI individuals. Genetic assessment in AAMI, MCI, and control subjects.

SETTING

General health centers and geriatric homes from northeastern Spain (Catalunya).

PARTICIPANTS

One hundred and four subjects presenting subjective memory complaints were selected and the AAMI and MCI criteria were applied. One hundred and twenty-four healthy Spanish subjects age 50 and older were defined as controls.

MEASUREMENTS

Memory, language, and frontal lobe functions were assessed using standard neuropsychological tests. The apolipoprotein E (apo E) polymorphism was obtained by using polymerase chain reaction (PCR) and HhaI restriction endonuclease.

RESULTS

Sixty-seven percent of previously diagnosed AAMI individuals could also be identified as MCI subjects. These MCI cases differed from those only-AAMI individuals both in neuropsychological and genetic analyses, performing worse not only on memory but also on language and frontal lobe tests and presenting high and low prevalences of the apo E epsilon 3/epsilon 4 and epsilon 3/epsilon 3 genotypes, respectively. The general AAMI sample of 93 individuals also differed from controls in the apo E genotype and allele distributions but these differences were no longer present after subtracting the MCI cases (63 subjects). These findings reflect that the differences between the memory impaired sample and the control sample regarding the apo E polymorphism were mainly attributable to MCI individuals and not to those who received only a diagnosis of AAMI alone.

CONCLUSIONS

Our findings suggest that among AAMI subjects, those who also fulfill the MCI criteria present a neuropsychological and genetic profile closer to that previously related to Alzheimer's disease than those individuals only eligible for a diagnosis of AAMI. However, our findings also suggest that using only the AAMI criteria still appears to select a population that differs genetically from the normal older population.

Relationship between severe amyloid angiopathy, apolipoprotein E genotype, and vascular lesions in Alzheimer's disease

In this brief review, we aim to describe the complex relationship between cerebral amyloid angiopathy (CAA), apolipoprotein E (ApoE), and cerebrovascular lesions in Alzheimer's disease (AD). First, we review the evidence that CAA is associated with, and may cause, specific types of vascular lesions (VLs). In addition to being a leading cause of lobar hemorrhages in the elderly, CAA has been implicated as a likely cause of small infarcts, microinfarcts, and incomplete infarctions in the deep white matter. We also review the role that ApoE4 (the major genetic risk factor for AD) has in predisposing toward CAA, coronary artery disease, and possibly toward cerebrovascular disease. Last, we provide evidence that the association between CAA and VLs is not a spurious one due to an increase in the ApoE4 genotype. Even within patient groups with the same ApoE genotype (specifically, E4/4 homozygotes and E3/3 homozygotes), our recent analyses have found significant increases in VLs in association with severe CAA. We discuss the implications of this finding as advancing a pathogenic role for severe CAA in producing many of the VLs commonly found in AD cases.

Apolipoprotein E phenotypes in healthy normal controls and demented subjects with Alzheimer's disease and vascular dementia in Mie Prefecture of Japan

In order to clarify the association between apolipoprotein E4 (ApoE4) and the pathogenesis of Alzheimer's disease (AD), we analyzed the distribution of the apolipoprotein E (ApoE) phenotypes and the frequency of the apo E alleles epsilon2, epsilon3, and epsilon4 in Japanese healthy controls (n = 1090, an average age of 51.2+/-12.6 years) and demented patients (n=103, mean age of 73.6+/-9.2 years). Demented subjects were divided into three subgroups: early-onset AD group (EOAD; n=25, mean age 63.0+/-6.2 years), late-onset AD group (LOAD; n=33, mean age 79.3+/-5.1 years), and vascular dementia group (VD; n=45, mean age 75.3+/-8.0 years). The apolipoprotein E phenotype was determined by isoelectric focusing and immunoblotting. There were no significant differences in the distribution of the apo E phenotypes by gender or age, and the estimated frequencies of epsilon2, epsilon3 and epsilon4 were 0.05, 0.86 and 0.09, respectively, in the normal controls. There was a significant difference in the distribution of the apo E phenotypes between LOAD and elderly controls aged more than 65 years (P<0.0001). The distribution of the apo E phenotypes in EOAD was the same as that in LOAD. The frequency of the epsilon4 allele was significantly higher in LOAD (0.35, P<0.0001) and EOAD (0.28, P<0.0001) than that in the control subjects (0.07), but not in VD (0.12, P=0.1630). The present findings suggest that ApoE4 is related with both EOAD and LOAD, but not with VD, and support the hypothesis that it is a genetic risk factor of AD.

Apolipoprotein E phenotypes in demented and cognitively impaired patients with and without cerebrovascular disease

Controversy exists regarding the apolipoprotein E (ApoE) epsilon4 allele association with vascular dementia (VaD), ranging from increased epsilon4 frequency, similar to that found for Alzheimer's disease (AD), to no association between the epsilon4 allele and VaD. To clarify further the relationship between ApoE alleles polymorphism and cerebrovascular disease (CVD) in demented and cognitively impaired patients, we examined the ApoE phenotypes in a sample of 280 patients: 155 with AD, 21 with VaD, 32 with mixed dementia (MD), 45 with mild cognitive impairment (MCI) but without CVD, and 27 in which vascular disease was the most probable cause of cognitive decline [vascular mild cognitive impairment (VMCI)]. Our results show that the frequency of the ApoE epsilon4 allele in patients over 70 years old with clinically diagnosed VaD and VMCI does not differ significantly from that of controls. In contrast, ApoE epsilon4 allele-bearing individuals had greater risk of having late-onset AD (OR = 8.8; 95% CI 3.7-21.0), or non-vascular cognitive impairment (OR = 7.0; 95% CI 2.5-19.0).

Angiotensin converting enzyme deletion allele in different kinds of dementia disorders

In order to verify the association of Angiotensin converting enzyme (ACE) gene with different kinds of dementia, as well as its association with APO-E (genotype), we performed ACE genotyping in subjects with late-onset probable Alzheimer's disease (LOAD, n = 64), early-onset probable Alzheimer's disease (EOAD, n = 32), possible Alzheimer's disease (pAD, n = 44), vascular dementia (VD, n = 12), age-associated memory impairment (AAMI, n = 15) and 40 healthy age-matched controls, who were previously characterized for APO-E. After the principal component analysis ACE D and Apo-Eepsilon4 alleles disclosed the highest prevalence in the cognitively impaired groups of subjects, Apo-Eepsilon4 being more specific for LOAD and pAD. ACE D allele seems to be an unspecific susceptibility factor for mental decline.