Familial and population-based studies of apolipoprotein E and Alzheimer's disease

Association between APOC1 polymorphism and Alzheimer's disease: a case-control study and meta-analysis

Background

Previous association studies examining the relationship between the APOC1 polymorphism and susceptibility to Alzheimer’s disease (AD) have shown conflicting results, and it is not clear if an APOC1 variant acts as a genetic risk factor in AD etiology across multiple populations.

Methods

To confirm the risk association between APOC1 and AD, we designed a case-control study and also performed a meta-analysis of previously published studies.

Results

Seventy-nine patients with AD and one hundred fifty-six unrelated controls were included in case-control study. No association was found between the variation of APOC1 and AD in stage 1 of our study. However, our meta-analysis pooled a total of 2092 AD patients and 2685 controls. The APOC1 rs11568822 polymorphism was associated with increased AD risk in Caucasians, Asians and Caribbean Hispanics, but not in African Americans. APOE ε4 carriers harboring the APOC1 insertion allele, were more prevalent in AD patients than controls (χ² = 119.46, OR = 2.79, 95% CI = 2.31–3.36, P<0.01).

Conclusions

The APOC1 insertion allele, in combination with APOE ε4, likely serves as a potential risk factor for developing AD.

Serotonin receptor, SERT mRNA and correlations with symptoms in males with alcohol dependence and suicide

OBJECTIVE

This study tested the hypothesis that abnormalities in components of the serotonin (5HT) system in the prefrontal cortex are associated with suicide in alcohol-dependent subjects. Second, we assessed the relationship of lifetime impulsivity and mood symptoms with prefrontal cortex 5-HT measures.

METHOD

Tissue was obtained from Brodmann's areas (BA) 9 and 24 in postmortem samples of individuals who were alcohol dependent with suicide (n = 5), alcohol dependent without suicide (n = 9) and normal controls (n = 5). Serotonin receptor (5HT) and serotonin reuptake transporter (SERT) mRNA were measured. Interviews with next of kin estimated lifetime impulsivity and mood symptoms in the last week of life.

RESULTS

Serotonin receptor 1A (5HT1A) mRNA in BA 9 was elevated in the alcohol dependence without suicide group compared with controls. In the alcohol dependence with suicide group, anxiety symptoms were associated with decreased BA 24 SERT mRNA and depressive symptoms with BA 9 5HT1A mRNA expression. In the alcohol dependent only group impulsivity is correlated with increased BA 9, and BA 24 serotonin receptor 2A mRNA.

CONCLUSION

Our data suggest region-specific change, rather than global serotonin blunting is involved in alcohol dependence and suicide. It also suggests that symptoms are differentially influenced by prefrontal cortex serotonin receptor mRNA levels.

Cholesterol metabolism and transport in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder, affecting millions of people worldwide. Apart from age, the major risk factor identified so far for the sporadic form of AD is possession of the epsilon4 allele of apolipoprotein E (APOE), which is also a risk factor for coronary artery disease (CAD). Other apolipoproteins known to play an important role in CAD such as apolipoprotein B are now gaining attention for their role in AD as well. AD and CAD share other risk factors, such as altered cholesterol levels, particularly high levels of low density lipoproteins together with low levels of high density lipoproteins. Statins--drugs that have been used to lower cholesterol levels in CAD, have been shown to protect against AD, although the protective mechanism(s) involved are still under debate. Enzymatic production of the beta amyloid peptide, the peptide thought to play a major role in AD pathogenesis, is affected by membrane cholesterol levels. In addition, polymorphisms in several proteins and enzymes involved in cholesterol and lipoprotein transport and metabolism have been linked to risk of AD. Taken together, these findings provide strong evidence that changes in cholesterol metabolism are intimately involved in AD pathogenic processes. This paper reviews cholesterol metabolism and transport, as well as those aspects of cholesterol metabolism that have been linked with AD.

Acute and long-term associations between ApoE genetic polymorphism, cortisol levels, and declarative memory performance in older adults

CONTEXT

For the past two decades, researchers have shown that elevated levels of circulating stress hormones may negatively impact cognitive performance in older adults. As well, genetic polymorphism of the apolipoprotein E gene (APOE) has been found to contribute to impairment in cognitive performance in old age. To date, only one study has reported a relationship between APOE status and cortisol levels, however the relationship was only found to be significant in dementia patients, with a trend observed in healthy controls.

OBJECTIVE

The goal of the present investigation was to examine the acute and long-term relationship between APOE status, cortisol secretion, and declarative memory performance in older adults.

DESIGN

Two sample cohorts were assessed. In the first cohort, 24-h basal serum cortisol levels were obtained once a year over eight years to assess changes in basal cortisol levels over time. Declarative memory was also obtained in this group at three time-points over five years. In the second cohort, basal and stress-induced cortisol levels as well as basal declarative memory was tested.

RESULTS

In the first cohort, E4 carriers were found to secrete higher serum cortisol levels than non-E4 carriers during the first 24-h visit (p=0.04) to the laboratory. However, this group difference did not remain over subsequent years. Furthermore, declarative memory performance over years did not significantly differ according to APOE status. In the second cohort, no significant group differences were found for basal or reactive cortisol levels (ps>0.05), and no group difference was found for acute declarative memory performance.

CONCLUSION

The findings in this study suggest minimal to no significant effect of APOE status on cortisol secretion or declarative memory in non-demented older adults.

Familial risk for Alzheimer's disease alters fMRI activation patterns

Alzheimer's disease poses a looming crisis for the health care system as well as society in general. The low efficacy of current treatments for those already affected with this disease has prompted the suggestion that interventions might be more successful if they were applied before the development of significant pathology, that is, when individuals are clinically asymptomatic. Currently, the field requires a sensitive and specific diagnostic tool for identifying those individuals destined to develop this disease. As a first step, we present here an analysis of cross-sectional data for 95 asymptomatic offspring (50-75 years of age) of autopsy-confirmed late-onset familial Alzheimer's disease cases and 90 age-matched controls, studied with functional magnetic resonance imaging (fMRI) to investigate brain activation patterns. Analysis of activation in response to a paired-associates memory paradigm found significantly different patterns in these groups. At-risk individuals showed more intense and extensive activation in the frontal and temporal lobes including the hippocampus during memory encoding, an increase unrelated to the APOE epsilon4 allele. They also showed decreased activation particularly in the cingulum and thalamus during both the encoding and recall phases of the task. These results demonstrate that asymptomatic individuals, at genetic risk for development of late-onset Alzheimer's disease by virtue of familial clustering, show functional activation patterns distinct from those without such risk more than a decade before their parent's onset age. While longitudinal study is needed to determine whether these patterns, or a subset of them, are predictive of disease onset, these findings suggest that functional neuroimaging holds promise as a method of identifying pre-clinical Alzheimer's disease.

Alzheimer’s Disease and Vascular Dementia

This chapter explores the frequency with which dementing illnesses occur in populations, their distributions by personal characteristics, and what is known about their causes and potential protective factors. The primary focus is on the most common forms of dementia: Alzheimer's disease and vascular dementia. The chapter summarizes clinical and pathologic features of Alzheimer's disease and vascular dementia, and highlights recent theories of how risk factors affect brain reserve. With the evolution of the epidemiology of dementia from case-control studies to prospective cohort studies has come a new set of methodological challenges. These include identification of representative populations, enhancing subject participation and retention in studies, the need to include institutionalized as well as community-dwelling populations, the non-standardized use of cognitive tests to screen for dementia, and the complexities of the diagnostic process itself. Finally, the chapter summarizes risk and protective factors for disease expression, including cardiovascular risk factors, lifestyle factors, and factors that affect brain reserve.

Evidence for parent of origin effect in late-onset Alzheimer disease

Evidence for a parent of origin effect in Alzheimer disease was obtained from a sample of 148 sibships on which affection status of the parents was sought using family history interviews. The parent study recruited families with two or more affected sibs for late onset AD utilizing rigorous diagnostic criteria. In 74 families, there was evidence of an affected parent, 49 maternal and 25 paternal. Genome scan data were analyzed for the sample as a whole and for the maternal and paternal families separately, using Genehunter-ASM. Seven regions with Z(lr) scores >or=2 were identified, four in maternal families (chr. 10,12,19,20) and three in paternal families (chr. 1,7,13). With the exception of the chromosome 10 finding, analysis by parent of origin greatly increased evidence of linkage in areas showing no linkage in the overall analyses. For example, a chr. 12 region reached a LOD = 2.29 among maternal families whereas the same region showed a LOD = 0.3 when all families were analyzed together. The strongest findings among maternal families (chr. 10 and 12) were followed up with fine mapping that resulted in an increase in maximum LOD scores from 2.7-3.2 on chr. 10, and 2.29-2.42 on chr. 12. These analyses highlight the importance of parent of origin effects in late-onset AD families and identify several genomic regions that may include genes linked to late-onset AD specific to disease transmission from the mother and require further investigation.

Genetic association of an apolipoprotein C-I (APOC1) gene polymorphism with late-onset Alzheimer's disease

Since a deletion/insertion polymorphism in the promoter region of the apolipoprotein C-I (APOC1) gene has been reported to be associated with late-onset Alzheimer's disease (LOAD), we examined the hypothesis in a Korean population with 120 LOAD cases and 132 age-matched controls. The frequency of APOC1 insertion allele (H2) was significantly increased in LOAD than in controls, giving an odds ratio of 3.3 (95% CI 2.0-5.5, P<0.0001). Logistic regression analysis revealed that the interaction model between APOE epsilon4 and APOC1 H2 yielded larger odds ratio than other models including either APOE epsilon4 or APOC1 H2 alone. In addition, the association between APOC1 H2 and LOAD remained significant after adjustment of the effect of APOE epsilon4 (P=0.036). These results support previous observations that the APOC1 might be an additional susceptibility gene for LOAD.

Family history of dementia and current depression in nondemented community-dwelling older adults

Since it has been postulated that mood disturbance in nondemented older adults may represent a prodromal feature of dementia for a subgroup of patients, it would be expected that patients with these symptoms would evidence a greater prevalence of family history of dementia. In a sample of 3225 community-dwelling cognitively intact elderly recruited from a free memory-screening program, we found that current depression was more common in participants with a positive versus a negative family history of dementia in first-degree relatives (17% versus 11%; Fisher's Exact Test, P < .0001). This relationship remained significant after controlling for age, education, gender, ethnicity, and Folstein Mini-Mental State Examination score (OR = 1.5; 95% CI = 1.2-1.9, Wald X2 = 15.5, P < .001). The results suggest that symptoms of depression may herald the onset of an incipient dementia syndrome in a subset of geriatric patients. Alternatively, the results may be indicative of familial aggregation of dementia and depression.

Association between Alzheimer's disease and a functional polymorphism in the Myeloperoxidase gene

A polymorphism in the Myeloperoxidase gene (MPO) has previously been demonstrated to be associated with gender-specific risk in an Alzheimer's Disease (AD) autopsy sample. We have investigated this polymorphism in our own samples of 226 Caucasian cases and 166 controls and 59 Hispanic cases and 75 controls. In Caucasians we find a significant association between MPO genotype and AD (P = 0.03), although we do not observe any effects of gender or any interaction with the APOE gene. Specifically, the MPO GG genotype contributes a 1.57-fold increased risk for AD. In Hispanics there was no effect of MPO genotype, or of MPO genotype in interaction with age or gender, on diagnosis of AD.

The genetic association between Cathepsin D and Alzheimer's disease

The aspartyl protease Cathepsin D has previously been suggested to play a role in the Alzheimer's disease (AD) process because of its ability to cleave the beta-amyloid precursor protein and the possibility that it may be one of the 'secretase' enzymes. A functional C-->T polymorphism in the Cathepsin D gene (CATD) has been reported to be associated with increased risk for AD in Caucasian case-control studies; specifically, the T-carrying genotypes confer increased risk. We have examined this association in our own Caucasian dataset of 210 AD cases and 120 controls, and in an additional Hispanic dataset comprising 79 AD cases and 112 controls. In Hispanics we find a modest interaction between CATD genotype and age of onset on risk for AD, such that the non-T-carrying genotype confers increased risk. In our Caucasian dataset we find no evidence for association between the CATD polymorphism and AD, although we do observe a small tendency towards an increase in the T-carrying genotypes in the case group, consistent with previous studies. We conducted an aggregate analysis of the published Caucasian datasets and found evidence that this CATD polymorphism (or another locus in linkage disequilibrium) does contribute significant, but small (<2%) risk for AD.

No association between the very low density lipoprotein receptor gene and late-onset Alzheimer's disease nor interaction with the apolipoprotein E gene in population-based and clinic samples

It is now commonly known that possession of one of the three common alleles of the apolipoprotein E (APOE) gene (allele epsilon 4) confers an increased risk for both familial and sporadic Alzheimer's disease (AD), and that this risk is dose-dependent. Other genes that may play a role in AD, either through independent association with the disease or through modification of the existing APOE risk, are under investigation. One such gene, the very low density lipoprotein receptor (VLDL-R) gene, was reported by Okuizumi et al. to be independently associated with AD in a Japanese population, but not interactive with the APOE4 conferred risk. Their clinic-based data set demonstrated a 2-fold increased risk conferred by the 5-repeat allele of a polymorphism in VLDL-R. As recruitment from a clinic rather than a population-based sample may result in a distortion of allele frequencies, as has been shown with APOE allele frequencies, it is important to investigate this association in a population-based study. We have genotyped both population and clinic-based AD data sets at this VLDL-R polymorphism, and we find no independent association between the VLDL-R gene and the occurrence of AD in either sample. Further, despite the biochemical relationship between the VLDL-R and APOE proteins, we find no significant statistical interaction between the alleles at these loci.

Is APOE--epsilon4 a risk factor for cognitive impairment in normal aging?

OBJECTIVES

To examine the relationship between APOE genotype and cognitive functioning in normal aging, and to determine whether this relationship was moderated by age or the presence of a number of disease conditions, including cardiovascular disease and diabetes.

METHODS

The sample was drawn from the Charlotte County Healthy Aging Study, a community-based, cross-sectional study of randomly selected older adults in Charlotte County, FL. A total of 413 older adults (mean age = 72.90 years) were examined in the current study. Participants completed tasks that indexed a variety of dimensions of cognitive functioning, including episodic memory, implicit memory, psychomotor speed, and attention. In addition, participants provided self-reported and objective indices of health status and were genotyped for APOE.

RESULTS

Mean-level results indicated that groups with and without the APOE-epsilon4 allele performed similarly on all domains of cognitive functioning. Significant age group differences were observed in episodic memory, psychomotor speed, and attention but not implicit memory. Significant gender differences were present for episodic memory and the Stroop test. Analyses also indicated that participants' age did not exert an impact on the relationship between APOE-epsilon4 and cognitive functioning. Further, the presence of cardiovascular disease or diabetes did little to moderate the relationship between APOE-epsilon4 and cognition.

CONCLUSIONS

The authors found no evidence for a relationship between presence of the APOE-epsilon4 allele and cognitive functioning. Further, age or the presence of a number of chronic conditions did not significantly moderate the effect of APOE genotype on cognitive performance. These results indicate that the presence of the epsilon4 allele is not a risk factor for cognitive impairment in normal aging.

Gender-specific association of the angiotensin converting enzyme gene with Alzheimer's disease

Epidemiological studies have demonstrated that risk factors for vascular disease are also risk factors for Alzheimer's disease (AD). The gene for the angiotensin converting enzyme (ACE) has recently been reported to be associated with risk for AD. We have investigated the possibility of such an association in 98 clinic-based and 73 community-based AD cases versus 175 community-based controls and find a gender-specific association of ACE genotype with AD in the female clinic population. These data suggest that gender may interact with genetic factors to influence risk for AD. Gender-specific risk for AD has been previously reported, and a biological rationale for involvement of ACE in the AD process is supported by studies exploring the relationship between AD and vascular risk factors such as hypertension. However, the results may also be a consequence of the known anomalies that arise in genetic association studies as a consequence of sample selection.

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.

The butyrylcholinesterase gene is neither independently nor synergistically associated with late-onset AD in clinic- and community-based populations

The K variant of the butyrylcholinesterase gene (BChE) was recently found to occur at an increased frequency in a late onset Alzheimer's disease (AD) population, specifically in individuals carrying the epsilon4 allele of the apolipoprotein E (APOE) gene. This suggested synergy between these two genes resulting in an increased risk of late-onset AD. We have genotyped 62 community-based and 329 clinic-based AD cases, and 201 community-based controls at BChE and APOE and find no independent association between BChE and AD nor interaction with APOE in risk for AD in either our clinic or community-based samples.

No association between the low density lipoprotein receptor-related protein (LRP) gene and late-onset Alzheimer's disease in a community-based sample

It is now commonly known that possession of the epsilon4 allele of the apolipoprotein E (APOE) gene confers an increased risk for both familial and sporadic Alzheimer's disease (AD), in a dose-dependent way. Other genes that may play a role in AD, either through independent association with the disease or through modification of the existing APOE risk, have been reported with conflicting results. One such gene, the low density lipoprotein receptor-related protein (LRP) gene, was recently reported by two groups to be associated with AD, although the groups identified different risk-conferring alleles. Both studies were based on clinic-derived AD populations (one American, one French), and both reported only marginally significant results. We have genotyped a community-based AD and control population at this LRP polymorphism and find no association between the variants at that polymorphism and the occurrence of AD. Further, despite the biochemical relationship between LRP and the ApoE protein, we find no significant statistical interaction between the alleles at these loci.