Identification of a protective allele against Alzheimer disease in the APOE gene promoter

Alzheimer disease (AD) risk is significantly influenced by the APOE2 and APOE4 alleles. In turn, the -491AT and TH1/E47cs polymorphisms alter APOE gene expression levels. To determine whether these two alleles exert any significant effect on AD development we have analysed the genotypes of the APOE promoter -491AT and Th1/E47cs polymorphisms in 163 AD patients and 155 controls divided into three age at onset/age dependent subgroups. Our study has detected a Th1/E47cs-T allele accumulation in healthy individuals over 75 years of age, which suggests it plays a protective role against AD. The Th1/E47cs-T allele may provide greater protection against AD than APOE2, although this awaits proof of Th1/E47cs-T allele overrepresentation in healthy individuals of other populations.     

Cholinesterase inhibitors influence APP metabolism in Alzheimer disease patients

Platelets mirror pathogenic alterations in the central nervous system of Alzheimer disease (AD) patients: an alteration of the Amyloid Precursor Protein (APP) forms pattern and decreased alpha-secretase activity--the non-amyloidogenic APP processing enzyme--were demonstrated. Platelets were analysed at baseline and after 30 days of cholinesterase inhibitor (ChEI) treatment (T30). ADAM10 levels, alpha- and beta-secretase activity were assessed measuring ADAM10 immunoreactivity, sAPPalpha release and the membrane-attached C-terminal fragments produced by beta- and alpha-secretase cleavage, that is, CTF99 and CTF83, respectively. ChEIs treatment rescues impaired APP metabolism increasing significantly ADAM10 levels (T30 vs. T0, P < 0.05), alpha-secretase activity (T30 vs. T0, P < 0.05) and reducing beta-secretase cleavage (T30 vs. T0, P < 0.05). Restoration of the balance between the mutually exclusive alpha- and beta-secretase pathway in APP processing caused by short-term ChEIs treatment potentially represents a key event in AD therapy linking in vivo cholinergic effect to APP metabolism. The use of platelets may represent a useful tool to follow molecular aspects of pharmacological response in AD patients.     

A family with Alzheimer disease and strokes associated with A713T mutation of the APP gene

Three members of an Italian family with autosomal dominant dementia and multiple strokes had the A713T mutation of the APP gene. The neuropathologic examination of the proband disclosed Alzheimer disease (AD) with severe cerebral amyloid angiopathy and multiple infarcts. This indicates that the A713T mutation of the APP gene, lying at the gamma-secretase cleavage site, can be responsible for AD with symptomatic cerebral amyloid angiopathy.     

Intracellular APP processing and A beta production in Alzheimer disease.

Senile plaques composed of A beta peptides are a histopathological hallmark of Alzheimer disease (AD). A role for A beta in the etiology of AD has been argued from analysis of mutations associated with a subset of early-onset familial AD (FAD). Expression of autosomal dominant mutations in the genes for the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2) in affected patients, cultured cells, or transgenic mice leads to increased production of total A beta or increased production of A beta ending at residue 42 (A beta42). Since A beta42 is the more amyloidogenic and toxic species in vitro and is the major component of amyloid senile plaques in vivo, overproduction of this peptide may play a crucial role in the pathogenesis of AD. Thus, an understanding of the production of A beta within the cell in normal and pathological conditions is critical to understanding early events in AD. Studies in cell culture have established that processing of APP to form A beta can occur at multiple locations within the cell and leads to the production of 2 pools of A beta: a secreted pool composed predominantly of A beta40 and a nonsecreted, intracellular pool composed preferentially of more amyloidogenic A beta42. The purpose of this review is to provide a summary of our current understanding of APP processing in the generation of the secreted and intracellular pools of A beta and to propose a model linking the intracellular pool to the formation of extracellular plaques and neuronal pathology in AD.     

Stroke and the risk of Alzheimer disease

BACKGROUND: Alzheimer disease (AD) and stroke are common in elderly individuals, but the relation between these 2 disorders remains uncertain. OBJECTIVE: To investigate the association between a clinical history of stroke and subsequent risk of AD. DESIGN: A cohort of 1766 Medicare recipients without dementia participated in a longitudinal follow-up study from 1992 through 1999 in upper Manhattan, New York, NY. History of stroke and presence of cardiovascular risk factors were ascertained at the onset of the study. Incidence rates for AD among those with and without stroke were calculated; proportional hazards ratios were computed using age at onset of the disease as the time-to-event variable. RESULTS: The annual incidence for AD was 5.2% among individuals with stroke vs 4% for those without stroke. The hazards ratio for AD among those with a history of stroke was 1.6 (95% confidence interval, 1.0-2.4) compared with those without stroke. Of the vascular risk factors, hypertension, diabetes, and heart disease, only diabetes related to risk of AD in the absence of stroke. Stroke remained weakly associated with AD in the absence of these factors, but risk significantly increased with the additional factors of hypertension (relative risk, 2.3; 95% confidence interval, 1.4-3.6), diabetes (relative risk, 4.6; 95% confidence interval, 2.2-9.5), or heart disease (relative risk, 2.0; 95% confidence interval, 1.2-3.2). CONCLUSIONS: Stroke is associated with AD among elderly individuals. The relation is strongest in the presence of known vascular risk factors. The observed association between stroke and AD might relate to an underlying systemic vascular disease process, or alternatively, to the additive effects of stroke and AD pathologic features, leading to an earlier age at onset of disease.     

Distinct patterns of APP processing in the CNS in autosomal-dominant and sporadic Alzheimer disease

Autosomal-dominant Alzheimer disease (ADAD) is a genetic disorder caused by mutations in Amyloid Precursor Protein (APP) or Presenilin (PSEN) genes. Studies from families with ADAD have been critical to support the amyloid cascade hypothesis of Alzheimer disease (AD), the basis for the current development of amyloid-based disease-modifying therapies in sporadic AD (SAD). However, whether the pathological changes in APP processing in the CNS in ADAD are similar to those observed in SAD remains unclear. In this study, we measured β-site APP-cleaving enzyme (BACE) protein levels and activity, APP and APP C-terminal fragments in brain samples from subjects with ADAD carrying APP or PSEN1 mutations (n = 18), patients with SAD (n = 27) and age-matched controls (n = 22). We also measured sAPPβ and BACE protein levels, as well as BACE activity, in CSF from individuals carrying PSEN1 mutations (10 mutation carriers and 7 non-carrier controls), patients with SAD (n = 32) and age-matched controls (n = 11). We found that in the brain, the pattern in ADAD was characterized by an increase in APP β-C-terminal fragment (β-CTF) levels despite no changes in BACE protein levels or activity. In contrast, the pattern in SAD in the brain was mainly characterized by an increase in BACE levels and activity, with less APP β-CTF accumulation than ADAD. In the CSF, no differences were found between groups in BACE activity or expression or sAPPβ levels. Taken together, these data suggest that the physiopathological events underlying the chronic Aβ production/clearance imbalance in SAD and ADAD are different. These differences should be considered in the design of intervention trials in AD.     

脑啡肽酶基因多态性与散发性阿尔茨海默病的关系研究

目的探讨脑啡肽酶(neprilysin,NEP)基因单核苷酸多态性与中国北方汉族散发性阿尔茨海默病(sporadic Alzheimer’s disease,SAD)的关系。方法临床确诊的99例中国北方汉族SAD患者及109例正常对照,提取外周血基因组DNA,聚合酶链反应-限制性片段长度多态性结合DNA直接测序法确定NEP基因rs989692位点及rs6776185位点基因型,分析上述两个位点单核苷酸多态性与AD的关系。结果 AD组和正常对照组NEP基因rs989692位点各等位基因频率及基因型分布无显著性差异(P>0.05);AD组NEP基因rs6776185位点A等位基因频率显著高于正常对照组(88.9%vs 81.2%,P=0.029),AA基因型频率显著高于正常对照组(80.8%vs 67.0%,P=0.024);携带A等位基因者,发生AD的风险是不携带A等位基因者的1.85倍(OR=1.85,95%CI 1.07~3.20);经载脂蛋白E基因(apolipoprotein E,Apo E)ε4等位基因及年龄分层比较,携带ε4基因及年龄<75岁组,AD组A等位基因及AA基因型分布频率仍明显高于正常对照组(P<0.05)。结论 NEP基因rs6776185位点A等位基因和AA基因型可能是中国北方汉族人群SAD的危险因素,可使AD发病年龄提前,并与Apo Eε4等位基因可能具有协同作用。     

Loneliness and risk of Alzheimer disease

CONTEXT: Social isolation in old age has been associated with risk of developing dementia, but the risk associated with perceived isolation, or loneliness, is not well understood. OBJECTIVE: To test the hypothesis that loneliness is associated with increased risk of Alzheimer disease (AD). DESIGN: Longitudinal clinicopathologic cohort study with up to 4 years of annual in-home follow-up. PARTICIPANTS: A total of 823 older persons free of dementia at enrollment were recruited from senior citizen facilities in and around Chicago, Ill. Loneliness was assessed with a 5-item scale at baseline (mean +/- SD, 2.3 +/- 0.6) and annually thereafter. At death, a uniform postmortem examination of the brain was conducted to quantify AD pathology in multiple brain regions and the presence of cerebral infarctions. MAIN OUTCOME MEASURES: Clinical diagnosis of AD and change in previously established composite measures of global cognition and specific cognitive functions. RESULTS: During follow-up, 76 subjects developed clinical AD. Risk of AD was more than doubled in lonely persons (score 3.2, 90th percentile) compared with persons who were not lonely (score 1.4, 10th percentile), and controlling for indicators of social isolation did not affect the finding. Loneliness was associated with lower level of cognition at baseline and with more rapid cognitive decline during follow-up. There was no significant change in loneliness, and mean degree of loneliness during the study was robustly associated with cognitive decline and development of AD. In 90 participants who died and in whom autopsy of the brain was performed, loneliness was unrelated to summary measures of AD pathology or to cerebral infarction. CONCLUSION: Loneliness is associated with an increased risk of late-life dementia but not with its leading causes.     

APOE and APOC1 promoter polymorphisms and the risk of Alzheimer disease in African American and Caribbean Hispanic individuals

BACKGROUND: The APOE epsilon4 allele is a genetic risk factor for Alzheimer disease (AD), though the strength of the association varies by ethnic group. Polymorphisms in regulatory sequences of APOE have also been related to AD, but the effects are inconsistent across studies. METHODS: We examined the association between AD and variants in 3 APOE promoters and in the promoter of the adjacent APOC1 gene in African American and Caribbean Hispanic individuals. Polymorphisms tested were the -491A/T, -427T/C, and -219G/T (Th1/E47cs) in the APOE promoter and the HpaI variant in the APOC1 promoter. Using standard research criteria for AD, overall odds ratios were computed and repeated stratified by presence or absence of APOE epsilon4. RESULTS: The APOC1 HpaI+ variant was associated with AD in Caribbean Hispanic individuals, but strong linkage disequilibrium with the APOE epsilon4 allele indicated that this was not an independent effect. No promoter variant in APOE or APOC1 was associated with AD before or after adjusting for age, education, sex, and multiple comparisons. Estimated haplotypes including -219G/T, APOE, and APOC1 differed significantly in Caribbean Hispanic patients and controls but not in African American participants. This effect was primarily owing to the -219G/T-APOE haplotype, but we did not detect significant allele-specific differences in promoter activity comparing reporter constructs containing the APOE -219G and -219 T alleles. CONCLUSION: These findings exclude a strong or independent influence of APOE or APOC1 promoter polymorphisms on the variation in APOE-related risk of AD in African American and Caribbean Hispanic individuals.     

Caloric intake and the risk of Alzheimer disease

BACKGROUND: Diet may play a role in Alzheimer disease (AD). OBJECTIVE: To examine the association between caloric intake and AD. METHODS: Elderly individuals free of dementia at baseline (N = 980) were followed for a mean of 4 years. Daily intake of calories, carbohydrates, fats, and protein were recalled using a semiquantitative food frequency questionnaire administered between the baseline and first follow-up visits. Proportional hazards models were used to examine the associations of quartiles of intake and incident AD, adjusting for confounders. RESULTS: There were 242 incident cases of AD during 4023 years of follow-up (6 cases per 100 person-years). Compared with individuals in the lowest quartile of caloric intake, those in the highest quartile had an increased risk of AD (hazard ratio, 1.5; 95% confidence interval [CI], 1.0-2.2). Among individuals with the apolipoprotein E epsilon4 allele, the hazard ratios of AD for the highest quartiles of calorie and fat intake were 2.3 (95% CI, 1.1-4.7) and 2.3 (95% CI, 1.1-4.9), respectively, compared with the lowest quartiles. The hazard ratios of AD for the highest quartiles of calorie and fat intake compared with the lowest quartiles in individuals without the apolipoprotein E epsilon4 allele were close to 1 and were not statistically significant (P =.83 and P =.61, respectively). CONCLUSION: Higher intake of calories and fats may be associated with higher risk of AD in individuals carrying the apolipoprotein E epsilon4 allele.     

Platelet APP, ADAM 10 and BACE alterations in the early stages of Alzheimer disease

Amyloid precursor protein (APP), ADAM 10, and beta-site-APP cleaving enzyme (BACE) alterations were evaluated in platelets of 31 patients with Alzheimer disease (AD) and 15 age-matched controls. A significant modification of these proteins and enzymes involved in the amyloid cascade was detected from the earliest clinically detectable disease stage. This observation suggests that AD is associated with an early metabolic derangement toward amyloidogenic pathways and supports the potential value of APP and secretase measurements for early diagnosis of AD.     

Conjugal Alzheimer disease: risk in children when both parents have Alzheimer disease

BACKGROUND: There is limited information regarding children's risk of Alzheimer disease (AD) if both parents are affected. OBJECTIVE: To determine the risk of AD in families in which both parents have AD. DESIGN: Retrospective study. SETTING: University research center. PARTICIPANTS: A total of 111 families in which both parents had a clinical diagnosis of AD. Main Outcome Measure Frequency of AD in the children of spouses with AD. RESULTS: The 111 couples with AD had 297 children surviving to adulthood; 22.6% of these adult children have developed AD. The risk of AD in these children increases with age, being 31.0% (58 of 187) in those older than 60 years and 41.8% (41 of 98) in those older than 70 years. Many children (79.0%) at risk in these families are still younger than 70 years, meaning that the occurrence of AD will increase in the coming years. A family history of AD beyond the parents did not change the risk of AD in the children but did reduce the median age at onset in affected children. The apolipoprotein E epsilon4 allele played an important part in this phenomenon but did not explain all cases of AD in the children. CONCLUSIONS: When both parents have AD, there is an increased risk of AD in their children beyond that of the general population. The role of family history and the specific genes involved in this phenomenon require a better definition.