Alzheimer's disease: diagnostics, prognostics and the road to prevention

Alzheimer's disease (AD) presents one of the leading healthcare challenges of the 21st century, with a projected worldwide prevalence of >107 million cases by 2025. While biomarkers have been identified, which may correlate with disease progression or subtype for the purpose of disease monitoring or differential diagnosis, a biomarker for reliable prediction of late onset disease risk has not been available until now. This deficiency in reliable predictive biomarkers, coupled with the devastating nature of the disease, places AD at a high priority for focus by predictive, preventive and personalized medicine. Recent data, discovered using phylogenetic analysis, suggest that a variable length poly-T sequence polymorphism in the TOMM40 gene, adjacent to the APOE gene, is predictive of risk of AD age-of-onset when coupled with a subject's current age. This finding offers hope for reliable assignment of disease risk within a 5-7 year window, and is expected to guide enrichment of clinical trials in order to speed development of preventative medicines.

Identification of miRNA changes in Alzheimer's disease brain and CSF yields putative biomarkers and insights into disease pathways

MicroRNAs have essential functional roles in brain development and neuronal specification but their roles in neurodegenerative diseases such as Alzheimer's disease (AD) is unknown. Using a sensitive qRT-PCR platform we identified regional and stage-specific deregulation of miRNA expression in AD patient brains. We used experimental validation in addition to literature to reveal how the deregulated brain microRNAs are biomarkers for known and novel pathways in AD pathogenesis related to amyloid processing, neurogenesis, insulin resistance, and innate immunity. We additionally recovered miRNAs from cerebrospinal fluid and discovered AD-specific miRNA changes consistent with their role as potential biomarkers of disease.

Rosiglitazone increases dendritic spine density and rescues spine loss caused by apolipoprotein E4 in primary cortical neurons

Convergent evidence has revealed an association between insulin resistance and Alzheimer's disease (AD), and the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, rosiglitazone, an insulin sensitizer and mitochondrial activator, improves cognition in patients with early or mild-to-moderate AD. Apolipoprotein (apo) E4, a major genetic risk factor for AD, exerts neuropathological effects through multiple pathways, including impairment of dendritic spine structure and mitochondrial function. Here we show that rosiglitazone significantly increased dendritic spine density in a dose-dependent manner in cultured primary cortical rat neurons. This effect was abolished by the PPAR-gamma-specific antagonist, GW9662, suggesting that rosiglitazone exerts this effect by activating the PPAR-gamma pathway. Furthermore, the C-terminal-truncated fragment of apoE4 significantly decreased dendritic spine density. Rosiglitazone rescued this detrimental effect. Thus, rosiglitazone might improve cognition in AD patients by increasing dendritic spine density.

Correlations between apolipoprotein E epsilon4 gene dose and whole brain atrophy rates

OBJECTIVE

The purpose of this study was to characterize the relationship between whole brain atrophy rates and three levels of genetic risk for Alzheimer's disease in cognitively normal persons. The authors previously found accelerated whole brain atrophy rates in patients with probable Alzheimer's disease by computing changes in brain volume from sequential magnetic resonance images (MRIs).

METHODS

The authors assessed 36 late-middle-aged persons from three genetic groups: those with two, one, and no copies of the apolipoprotein E (APOE) epsilon4 allele, a common Alzheimer's disease susceptibility gene. The participants had clinical ratings, neuropsychological tests, and volumetric T1-weighted MRIs during a baseline visit and again approximately 2 years later. Two different image-analysis techniques, brain boundary shift integration and iterative principal component analysis, were used to compute whole brain atrophy rates.

RESULTS

While there were no baseline, follow-up, or between-visit differences in the clinical ratings or neuropsychological test scores among the three subject groups, whole brain atrophy rates were significantly greater in the epsilon4 homozygote group than in noncarriers and were significantly correlated with epsilon4 gene dose (i.e., the number of epsilon4 alleles in a person's APOE genotype).

CONCLUSION

Since APOE epsilon4 gene dose is associated with an increased risk of Alzheimer's disease and a younger median age at dementia onset, this study suggests an association between the risk of Alzheimer's disease and accelerated brain atrophy rates before the onset of cognitive impairment.

APOE2 allele increased in tardive dyskinesia

Ninety-seven inpatients with tardive dyskinesia (average AIMS score = 13), the majority of whom were schizophrenic, were studied. Forty patients were Caucasian, and 57 were African-American. The APOE genotypes of these patients were compared to previously published genotypes of controls and with previously published studies of APOE genotypes in patients with schizophrenia. There were no significant differences in APOE allele frequencies comparing the African-American tardive dyskinesia population and the African-American control groups. In contrast, significant (< 0.05) P values were obtained comparing the Caucasian tardive dyskinesia population to the Caucasian controls, when comparing allele frequencies and genotypic frequencies. This study suggests that Caucasians bearing an APOE2 allele are at increased risk of developing tardive dyskinesia, whereas African-Americans are not. APOE genotype-specific risks of both tardive dyskinesia and Alzheimer's disease that vary across populations could be due to recruitment of patients or controls or could be due to modifying effects of differing genetic or environmental backgrounds. The mechanism by which the APOE2 allele increases risk of tardive dyskinesia is not known. Further information about the mechanisms of increased risk of tardive dyskinesia could result in stratification of prescribing practices weighing the costs of medications against the relative risk of side effects.

Complex disease-associated pharmacogenetics: drug efficacy, drug safety, and confirmation of a pathogenetic hypothesis (Alzheimer's disease)

Safety and efficacy pharmacogenetics can be applied successfully to the drug discovery and development pipeline at multiple phases. We review drug-target screening using high throughput SNP associations with complex diseases testing more than 1,800 candidate targets with approximately 7,000 SNPs. Alzheimer's disease data are provided as an example. The supplementation of target-selected screening with genome-wide SNP association, to also define susceptibility genes and relevant disease pathways for human diseases, is discussed. Applications for determining predictive genetic or genomic profiles, or derived biomarkers, for drug efficacy and safety during clinical development are exemplified by several successful experiments at different phases of development. A Phase I-IIA study of side effects using an oral drug for the treatment of breast cancer is used as an example of early pipeline pharmacogenetics to predict side effects and allow optimization of dosing. References are provided for several other recently published genetic association studies of adverse events during drug development. We illustrate the early identification of gene variant candidates related to efficacy in a Phase IIA obesity drug trial to generate hypotheses for testing in subsequent development. How these genetic data generated in Phase IIA are subsequently incorporated as hypotheses into later Phase clinical protocols is discussed. A Phase IIB clinical trial for Alzheimer's disease is described that exemplifies the major pipeline decision between program attrition and further clinical development. In this case, there was no significant improvement in 511 intention-to-treat patients but, applying a confirmed prognostic biomarker (APOE4) to segment the clinical trial population, all three doses of rosiglitazone demonstrated improvement in patients who did not carry the APOE4 allele. The data for the APOE4 carriers demonstrated no significant improvement but suggested that there may be a need for higher doses. Thus, a development program that would have been terminated progressed to Phase III registration trials based on the results of prospective efficacy pharmacogenetic analyses. The implications of using APOE genotype as a biomarker to predict efficacy and possibly dose, as well as supporting the basic neurobiology and pharmacology that provided the original target validation, is discussed. Citations are provided that support a slow neurotoxic effect over many years of a specific fragment of apoE protein (over-produced by apoE4 substrate compared to apoE3) on mitochondria and the use of rosiglitazone to increase mitochondrial biogenesis and improve glucose utilization. Pharmacogenetics is currently being used across the pipeline to prevent attrition and to create safer and more effective medicines.

Clusters of adjacent and similarly expressed genes across normal human tissues complicate comparative transcriptomic discovery

Transcriptomic techniques are valuable tools with which to validate genetic and biological hypotheses and are now widely available for research. However, with the exception of tumor biology, comparative genomics analyses have been difficult to use as discovery engines to describe biologically relevant expression changes. We propose that physical proximity of human genes correlates with similar mRNA expression, so that increased expression might include a disease-relevant gene and many other genes in the adjacent region. To increase the efficiency of combining susceptibility gene mapping and interpretation of transcriptomics, we developed a method to identify clusters of adjacent and similarly expressed genes. Gene expression profiles for 28,945 genes across 101 normal human tissues were obtained from the Gene Logic BioExpress system. The expression similarity for genes in sliding-windows was measured using average pair-wise Pearson correlation coefficients. We identified 187 clusters (p < 10e-4) of co-regulated genes, including 2648 genes, or 9.1% of all genes considered and termed these "clusters of adjacent and similarly expressed genes" (CASEGs). Genes in 15 (8.2%) of these clusters demonstrate a significant co-expression enrichment (p < 10e-10). This study demonstrates the coordinate expression of neighboring genes and provides a comprehensive view of expression-based compartmentalization of the human genome, which can be overlaid on genetic susceptibility gene maps.

Efficacy of rosiglitazone in a genetically defined population with mild-to-moderate Alzheimer's disease

Mild-to-moderate AD patients were randomized to placebo or rosiglitazone (RSG) 2, 4 or 8 mg. Primary end points at Week 24 were mean change from baseline in AD Assessment Scale-Cognitive (ADAS-Cog) and Clinician's Interview-Based Impression of Change Plus Caregiver Input global scores in the intention-to-treat population (N=511), and results were also stratified by apolipoprotein E (APOE) genotype (n=323). No statistically significant differences on primary end points were detected between placebo and any RSG dose. There was a significant interaction between APOE epsilon4 allele status and ADAS-Cog (P=0.014). Exploratory analyses demonstrated significant improvement in ADAS-Cog in APOE epsilon4-negative patients on 8 mg RSG (P=0.024; not corrected for multiplicity). APOE epsilon4-positive patients did not show improvement and showed a decline at the lowest RSG dose (P=0.012; not corrected for multiplicity). Exploratory analyses suggested that APOE epsilon4 non-carriers exhibited cognitive and functional improvement in response to RSG, whereas APOE epsilon4 allele carriers showed no improvement and some decline was noted. These preliminary findings require confirmation in appropriate clinical studies.

Correlations between apolipoprotein E epsilon4 gene dose and brain-imaging measurements of regional hypometabolism

Patients with Alzheimer's disease (AD) have abnormally low positron emission tomography (PET) measurements of the cerebral metabolic rate for glucose (CMRgl) in regions of the precuneus and the posterior cingulate, parietotemporal, and frontal cortex. Apolipoprotein E (APOE) epsilon4 gene dose (i.e., the number of epsilon4 alleles in a person's APOE genotype) is associated with a higher risk of AD and a younger age at dementia onset. We previously found that cognitively normal late-middle-aged APOE epsilon4 carriers have abnormally low CMRgl in the same brain regions as patients with probable Alzheimer's dementia. In a PET study of 160 cognitively normal subjects 47-68 years of age, including 36 epsilon4 homozygotes, 46 heterozygotes, and 78 epsilon4 noncarriers who were individually matched for their gender, age, and educational level, we now find that epsilon4 gene dose is correlated with lower CMRgl in each of these brain regions. This study raises the possibility of using PET as a quantitative presymptomatic endophenotype to help evaluate the individual and aggregate effects of putative genetic and nongenetic modifiers of AD risk.

A single-nucleotide polymorphism tagging set for human drug metabolism and transport

Interindividual variability in drug response, ranging from no therapeutic benefit to life-threatening adverse reactions, is influenced by variation in genes that control the absorption, distribution, metabolism and excretion of drugs. We genotyped 904 single-nucleotide polymorphisms (SNPs) from 55 such genes in two population samples (European and Japanese) and identified a set of tagging SNPs that represents the common variation in these genes, both known and unknown. Extensive empirical evaluations, including a direct assessment of association with candidate functional SNPs in a new, larger population sample, validated the performance of these tagging SNPs and confirmed their utility for linkage-disequilibrium mapping in pharmacogenetics. The analyses also suggest that rare variation is not amenable to tagging strategies.

Apolipoprotein E is associated with age at onset of amyotrophic lateral sclerosis

Apolipoprotein E (APOE) is a confirmed risk factor for Alzheimer disease. APOE is also involved in several other neurodegenerative disorders, including Parkinson disease and multiple sclerosis. Previous studies of amyotrophic lateral sclerosis (Lou Gehrig disease, ALS) have investigated the effect of APOE on the risk of developing ALS, age at onset, site of onset, and duration of the disease. The results have been inconsistent, possibly due to small sample sizes and complete reliance on case-control data. No family-based association studies were performed. To address these limitations, we investigated the relationship between APOE functional polymorphisms and age at onset of ALS in a large set of 508 families. We treated age at onset as a quantitative trait and performed family-based association analysis using the TDTQ5 method. APOE-2 is protective against earlier onset (P =0.001) with an average age at onset of APOE-2 carriers approximately 3 years later than that of non-APOE-2 carriers. Similar to our previous report, we did not find APOE associated with ALS risk. Our findings suggest that APOE may express its strongest effect through age at onset rather than on risk.

Comprehensive association analysis of APOE regulatory region polymorphisms in Alzheimer disease

Several recent case-control studies have examined the association between single nucleotide polymorphisms (SNPs) in the promoter region of the apolipoprotein E gene (APOE) and risk of Alzheimer disease (AD), with conflicting results. We assessed the relation between five APOE region SNPs and risk of AD in both case-control and family-based analyses. We observed a statistically significant association with the +5361T allele in the overall case-control analysis (P value=0.04) after adjusting for the known effect of the APOE-4 allele. Further analysis revealed this association to be limited to carriers of the APOE-4 allele. Age-stratified analyses in the patients with age at onset of 80 years or greater and age-matched controls showed that the -219T allele (P value=0.009) and the +113C allele (P value=0.03) are associated with increased risk of AD. Despite these findings, haplotype and family-based association analyses were unable to provide evidence that the APOE region SNPs influenced risk of AD independent of the APOE-4 allele. In addition to risk, we tested for association between the SNPs and age at onset of AD, but found no association in the case-control or family based analyses. In conclusion, SNPs +5361, or a SNP in strong linkage disequilibrium, may confer some additional risk for developing AD beyond the risk due to APOE-4; however, the effect independent of APOE-4 is likely to be small.

A Gilbert's syndrome UGT1A1 variant confers susceptibility to tranilast-induced hyperbilirubinemia

Tranilast (N-(3'4'-demethoxycinnamoyl)-anthranilic acid (N-5)) is an investigational drug for the prevention of restenosis following percutaneous transluminal coronary revascularization. An increase in bilirubin levels was observed in 12% of patients upon administration of tranilast in a phase III clinical trial. To identify the potential genetic factors that may account for the drug-induced hyperbilirubinemia, we examined polymorphisms in the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene in over a thousand patients. Our results suggested that the TA repeat polymorphism in UGT1A1, which predisposes some individuals to Gilbert's syndrome, predicted the susceptibility to tranilast-induced hyperbilirubinemia. The (TA)(7)/(TA)(7) genotype was present in 39% of the 127 hyperbilirubinemic patients vs 7% of the 909 controls (P=2 x 10(-22)). Rapid identification of genetic factors accounting for the observed adverse effect during the course of a double-blind clinical trial demonstrated the potential application of pharmacogenetics in the clinical development of safe and effective medicines.

Analysis of European mitochondrial haplogroups with Alzheimer disease risk

We examined the association of mtDNA variation with Alzheimer disease (AD) risk in Caucasians (989 cases and 328 controls) testing the effect of individual haplogroups and single nucleotide polymorphisms (SNPs). Logistic regression analyses were used to assess risk of haplogroups and SNPs with AD in both main effects and interaction models. Males classified as haplogroup U showed an increase in risk (OR = 2.30; 95% CI, 1.03-5.11; P = 0.04) of AD relative to the most common haplogroup H, while females demonstrated a significant decrease in risk with haplogroup U (OR = 0.44 ; 95% CI, 0.24-0.80; P = 0.007). Our results were independent of APOE genotype, demonstrating that the effect of mt variation is not confounded by APOE4 carrier status. We suggest that variations within haplogroup U may be involved in AD expression in combination with environmental exposures or nuclear proteins other than APOE.

Periventricular leukomalacia is common after neonatal cardiac surgery

OBJECTIVES

Periventricular leukomalacia is necrosis of the cerebral white matter adjacent to the lateral ventricles and results from injury to immature oligodendroglia. In infants without congenital heart disease, periventricular leukomalacia is associated with an increased incidence of developmental delay and attention deficit/hyperactivity disorder. The incidence of periventricular leukomalacia and the risk factors for development of periventricular leukomalacia after infant cardiac surgery are not known.

METHODS

Magnetic resonance imaging of the brain was performed 6 to 14 days after cardiac surgery utilizing cardiopulmonary bypass with or without deep hypothermic circulatory arrest in 105 neonates and infants < or = 6 months of age.

RESULTS

Median age at surgery was 6 days (range 1-178), with 82 neonates (age < or = 30 days). Periventricular leukomalacia was found in 44 of the neonates (54%) compared with 1 of 23 infants (4%). Forward logistic regression using age at surgery as a continuous variable identified a model containing longer total support time (cardiopulmonary bypass plus deep hypothermic circulatory arrest), lower systolic blood pressure at cardiac intensive care unit admission postoperatively, lower minimum diastolic blood pressure, and Po(2) in the first 48 hours after surgery. When age at surgery was considered as a dichotomous variable (neonate versus infant), younger age at surgery replaced systolic blood pressure, Po(2), and total support time in the model. Lower minimum diastolic blood pressure was a significant risk factor in both models.

CONCLUSIONS

Periventricular leukomalacia was found in >50% of neonates after cardiac surgery but rarely in older infants. Hypoxemia and hypotension in the early postoperative period, particularly diastolic hypotension, may be important risk factors for periventricular leukomalacia.

Functional brain abnormalities in young adults at genetic risk for late-onset Alzheimer's dementia

Fluorodeoxyglucose positron emission tomography (PET) studies have found that patients with Alzheimer's dementia (AD) have abnormally low rates of cerebral glucose metabolism in posterior cingulate, parietal, temporal, and prefrontal cortex. We previously found that cognitively normal, late-middle-aged carriers of the apolipoprotein E epsilon4 allele, a common susceptibility gene for late-onset Alzheimer's dementia, have abnormally low rates of glucose metabolism in the same brain regions as patients with probable AD. We now consider whether epsilon4 carriers have these regional brain abnormalities as relatively young adults. Apolipoprotein E genotypes were established in normal volunteers 20-39 years of age. Clinical ratings, neuropsychological tests, magnetic resonance imaging, and PET were performed in 12 epsilon4 heterozygotes, all with the epsilon3/epsilon4 genotype, and 15 noncarriers of the epsilon4 allele, 12 of whom were individually matched for sex, age, and educational level. An automated algorithm was used to generate an aggregate surface-projection map that compared regional PET measurements in the two groups. The young adult epsilon4 carriers and noncarriers did not differ significantly in their sex, age, educational level, clinical ratings, or neuropsychological test scores. Like previously studied patients with probable AD and late-middle-aged epsilon4 carriers, the young epsilon4 carriers had abnormally low rates of glucose metabolism bilaterally in the posterior cingulate, parietal, temporal, and prefrontal cortex. Carriers of a common Alzheimer's susceptibility gene have functional brain abnormalities in young adulthood, several decades before the possible onset of dementia.

Glutathione S-transferase omega-1 modifies age-at-onset of Alzheimer disease and Parkinson disease

We previously reported genetic linkage of loci controlling age-at-onset in Alzheimer disease (AD) and Parkinson's disease (PD) to a 15 cM region on chromosome 10q. Given the large number of genes in this initial starting region, we applied the process of 'genomic convergence' to prioritize and reduce the number of candidate genes for further analysis. As our second convergence factor we performed gene expression studies on hippocampus obtained from AD patients and controls. Analysis revealed that four of the genes [stearoyl-CoA desaturase; NADH-ubiquinone oxidoreductase 1 beta subcomplex 8; protease, serine 11; and glutathione S-transferase, omega-1 (GSTO1)] were significantly different in their expression between AD and controls and mapped to the 10q age-at-onset linkage region, the first convergence factor. Using 2814 samples from our AD dataset (1773 AD patients) and 1362 samples from our PD dataset (635 PD patients), allelic association studies for age-at-onset effects in AD and PD revealed no association for three of the candidates, but a significant association was found for GSTO1 (P=0.007) and a second transcribed member of the GST omega class, GSTO2 (P=0.005), located next to GSTO1. The functions of GSTO1 and GSTO2 are not well understood, but recent data suggest that GSTO1 maybe involved in the post-translational modification of the inflammatory cytokine interleukin-1beta. This is provocative given reports of the possible role of inflammation in these two neurodegenerative disorders.

Apolipoprotein E genotype and neurodevelopmental sequelae of infant cardiac surgery

BACKGROUND

There has been increasing recognition of adverse neurodevelopmental sequelae in some children after repair of congenital heart defects. Even among children with the same cardiac defect, significant interindividual variation exists in developmental outcome. Polymorphisms of apolipoprotein E have been identified as a risk factor for worse neurologic recovery after central nervous system injury.

METHODS

A single-institution prospective study of patients <or=6 months of age undergoing cardiopulmonary bypass for repair of congenital heart defects was undertaken to evaluate the association between apolipoprotein E genotype and postoperative neurodevelopmental dysfunction. Developmental outcomes were evaluated at 1 year of age by using the Bayley Scales of Infant Development.

RESULTS

One-year evaluation was performed in 244 patients. After adjustment for preoperative and postoperative covariates-including gestational age, age at operation, sex, race, socioeconomic status, cardiac defect, and use of deep hypothermic circulatory arrest-the apolipoprotein E epsilon2 allele was associated with a worse neurologic outcome as assessed by the Psychomotor Developmental Index of the Bayley Scales of Infant Development (P =.036). Patients with the apolipoprotein E epsilon2 allele had approximately a 7-point decrease in the Psychomotor Developmental Index.

CONCLUSIONS

Apolipoprotein E epsilon2 allele carriers had significantly lower Psychomotor Development Index scores at 1 year of age after infant cardiac surgery. The effect was independent of ethnicity, socioeconomic status, cardiac defect, and use of deep hypothermic circulatory arrest. An effect of the apolipoprotein E epsilon4 allele was not detected. Genetic polymorphisms that decrease neuroresiliency and impair neuronal repair after central nervous system injury are important risk factors for neurodevelopmental dysfunction after infant cardiac surgery.

Ordered-subsets linkage analysis detects novel Alzheimer disease loci on chromosomes 2q34 and 15q22

Alzheimer disease (AD) is a complex disorder characterized by a wide range, within and between families, of ages at onset of symptoms. Consideration of age at onset as a covariate in genetic-linkage studies may reduce genetic heterogeneity and increase statistical power. Ordered-subsets analysis includes continuous covariates in linkage analysis by rank ordering families by a covariate and summing LOD scores to find a subset giving a significantly increased LOD score relative to the overall sample. We have analyzed data from 336 markers in 437 multiplex (>/=2 sampled individuals with AD) families included in a recent genomic screen for AD loci. To identify genetic heterogeneity by age at onset, families were ordered by increasing and decreasing mean and minimum ages at onset. Chromosomewide significance of increases in the LOD score in subsets relative to the overall sample was assessed by permutation. A statistically significant increase in the nonparametric multipoint LOD score was observed on chromosome 2q34, with a peak LOD score of 3.2 at D2S2944 (P=.008) in 31 families with a minimum age at onset between 50 and 60 years. The LOD score in the chromosome 9p region previously linked to AD increased to 4.6 at D9S741 (P=.01) in 334 families with minimum age at onset between 60 and 75 years. LOD scores were also significantly increased on chromosome 15q22: a peak LOD score of 2.8 (P=.0004) was detected at D15S1507 (60 cM) in 38 families with minimum age at onset >/=79 years, and a peak LOD score of 3.1 (P=.0006) was obtained at D15S153 (62 cM) in 43 families with mean age at onset >80 years. Thirty-one families were contained in both 15q22 subsets, indicating that these results are likely detecting the same locus. There is little overlap in these subsets, underscoring the utility of age at onset as a marker of genetic heterogeneity. These results indicate that linkage to chromosome 9p is strongest in late-onset AD and that regions on chromosome 2q34 and 15q22 are linked to early-onset AD and very-late-onset AD, respectively.

The Q7R Saitohin gene polymorphism is not associated with Alzheimer disease

Previous studies have reported conflicting results regarding the association of the Q7R polymorphism in the Saitohin gene with late-onset Alzheimer disease (AD). Given that AD is a tauopathy but no mutations or polymorphisms in Tau have been consistently associated with AD, and that Saitohin is nested in intron 9 of Tau and shares a similar expression pattern, we tested this association in 690 multiplex AD families and in a case-control sample (903 patients and 320 controls). We found no evidence of significant association of this polymorphism with risk of AD using family-based and case-control tests of association.

ApoE genotype-specific inhibition of apoptosis

Endothelial cell apoptosis can be initiated by withdrawing growth factors or serum, and is inhibited by HDL. Our results show that the total lipoprotein population from apolipoprotein E 4/4 (APOE4/4) sera is less anti-apoptotic than total lipoproteins from other APOE genotypes, as measured by caspase 3/7 activity. Moreover, APOE4/4 VLDL antagonizes the antiapoptotic activity of HDL by a mechanism requiring binding of apoE4 on VLDL particles to an LDL family receptor. This ability of APOE4/4 VLDL to inhibit the antiapoptotic effects of HDL presents a potential mechanism by which the expression of several diseases, including atherosclerosis, is enhanced by the APOE4 genotype.

APOE genotype is a risk factor for neuropathy severity in diabetic patients

This cross-sectional study tested the hypothesis that APOE genotype is a risk factor for diabetic neuropathy severity. A model with age, duration of diabetes, and APOE genotype was found to predict (p = 0.0083) severity on the Neuropathy Impairment Score in the Lower Limbs (NISLL). Considering genotype alone, patients with APOE 3/4 and 4/4 genotypes had 3 more NISLL points than patients with other genotypes. This impact on severity is equivalent to having 15 extra years of age or diabetes duration.

Enhanced biological phosphorus removal in a sequencing batch reactor using propionate as the sole carbon source

An enhanced biological phosphorus removal (EBPR) system was developed in a sequencing batch reactor (SBR) using propionate as the sole carbon source. The microbial community was followed using fluorescence in situ hybridization (FISH) techniques and Candidatus 'Accumulibacter phosphatis' were quantified from the start up of the reactor until steady state. A series of SBR cycle studies was performed when 55% of the SBR biomass was Accumulibacter, a confirmed polyphosphate accumulating organism (PAO) and when Candidatus 'Competibacter phosphatis', a confirmed glycogen-accumulating organism (GAO), was essentially undetectable. These experiments evaluated two different carbon sources (propionate and acetate), and in every case, two different P-release rates were detected. The highest rate took place while there was volatile fatty acid (VFA) in the mixed liquor, and after the VFA was depleted a second P-release rate was observed. This second rate was very similar to the one detected in experiments performed without added VFA.A kinetic and stoichiometric model developed as a modification of Activated Sludge Model 2 (ASM2) including glycogen economy, was fitted to the experimental profiles. The validation and calibration of this model was carried out with the cycle study experiments performed using both VFAs. The effect of pH from 6.5 to 8.0 on anaerobic P-release and VFA-uptake and aerobic P-uptake was also studied using propionate. The optimal overall working pH was around 7.5. This is the first study of the microbial community involved in EBPR developed with propionate as a sole carbon source along with detailed process performance investigations of the propionate-utilizing PAOs.

The effect of GAOs (glycogen accumulating organisms) on anaerobic carbon requirements in full-scale Australian EBPR (enhanced biological phosphorus removal) plants

Glycogen-accumulating organisms (GAOs) were present in six full-scale plants investigated and in all but one made a significant contribution to the amount of volatile fatty acid (VFA) taken up anaerobically. While most plants surveyed contain GAOs, it was demonstrated that it is possible for a full-scale plant to operate with an insignificant GAO population. "Candidatus Accumulibacter phosphatis" were the significant polyphosphate-accumulating organisms (PAOs) in all plants surveyed. "Candidatus Competibacter phosphatis" were found in all plants along with other possible GAOs that were observed but not identified. A significant GAO population will increase the carbon requirements by removing VFA that could otherwise have been used by PAOs. Process optimization minimizing GAOs in full-scale plants would lead to a more efficient use of VFA.

APOE and the regulation of microglial nitric oxide production: a link between genetic risk and oxidative stress

The mechanism linking the APOE4 gene with increased susceptibility for Alzheimer's disease (AD) and poorer outcomes following closed head injury and stroke is unknown. One potential link is activation of the innate immune system in the CNS. Our previously published data demonstrated that apolipoprotein E regulates production of nitric oxide, a critical cytoactive factor released by immune active macrophages. To determine if immune regulation is different in the presence of apolipoprotein E4 compared to apolipoprotein E3, we have measured NO production by peritoneal and CNS macrophages (microglia) cultured from transgenic mice that only express the human apoE4 or apoE3 protein isoform. Significantly more NO was produced in APOE4 mice compared to APOE3 transgenic mice that only express human apoE3 protein. Similarly, monocyte derived macrophages from humans carrying APOE4 gene alleles also produce significantly greater NO than those individuals with APOE3. The mechanism for this isoform-specific difference in NO production is not known and multiple sites in the NO production pathway may be affected. Expression of inducible nitric oxide synthase (iNOS) mRNA and protein are not significantly different between the APOE3 and APOE4 mice, suggesting that induction of iNOS is not a primary cause of the increased NO production in APOE4 animals. One alternative regulatory mechanism that demonstrates isoform specificity is arginine transport, which is greater in microglia from APOE4 transgenic mice compared to microglia from APOE3 mice. Increased transport is consistent with an increased production of NO and may reflect a direct or indirect effect of the APOE genotype on microglial arginine uptake and microglial activation in general. Overall, greater NO production in APOE4 carriers where characteristically high levels of oxidative/nitrosative stress are found in diseases such as AD provides a mechanism that potentially explains the genetic association between APOE4 and human diseases.

Apolipoprotein E epsilon4 and risk of mortality in African American and white older community residents

PURPOSE

The goal of this study was to determine whether the epsilon4 allele of apolipoprotein E is predictive of mortality in a community-based sample.

DESIGN AND METHODS

Of the stratified random household sample of 4,162 participants age 65 years and older enrolled in the Duke site of the Established Populations for Epidemiologic Studies of the Elderly, those included in the present study were the 1,998 who were genotyped for apolipoprotein E (alleles epsilon2, epsilon3, and epsilon4) six years after baseline, and for whom survival status eight years later was known by search of the National Death Index. Information on demographic characteristics, physical and mental health status, functional status, and health services use was determined by structured questionnaires administered in person in the home.

RESULTS

The epsilon4 allele did not predict mortality for the group as a whole, or for those who were cognitively impaired. It did predict mortality for those who reported having had a heart attack or stroke.

IMPLICATIONS

The apolipoprotein epsilon4 allele-although a risk factor for Alzheimer's disease, heart disease, and stroke-was only found to be a risk factor for mortality for those community residents who had had a heart attack or stroke. Otherwise, for this community-based sample, 71 years of age and older, it did not predict time to death and was not a risk factor for mortality.

FH, Goetz CG, Mastaglia F, Stajich JM, Gibson RA, Middleton LT, Saunders AM, Scott BL, Small GW, Nicodemus KK, Reed AD, Schmechel DE, Welsh-Bohmer KA, Conneally PM, Roses AD, Gilbert JR, Vance JM, Haines JL, Pericak-Vance MA. Age at onset in two common neurodegenerative diseases is genetically controlled

To identify genes influencing age at onset (AAO) in two common neurodegenerative diseases, a genomic screen was performed for AAO in families with Alzheimer disease (AD; n=449) and Parkinson disease (PD; n=174). Heritabilities between 40%--60% were found in both the AD and PD data sets. For PD, significant evidence for linkage to AAO was found on chromosome 1p (LOD = 3.41). For AD, the AAO effect of APOE (LOD = 3.28) was confirmed. In addition, evidence for AAO linkage on chromosomes 6 and 10 was identified independently in both the AD and PD data sets. Subsequent unified analyses of these regions identified a single peak on chromosome 10q between D10S1239 and D10S1237, with a maximum LOD score of 2.62. These data suggest that a common gene affects AAO in these two common complex neurodegenerative diseases.

Association of polymorphisms in the apolipoprotein E region with susceptibility to and progression of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system, with a complex etiology that includes a strong genetic component. The contribution of the major histocompatibility complex (MHC) has been established in numerous genetic linkage and association studies. In addition to the MHC, the chromosome 19q13 region surrounding the apolipoprotein E (APOE) gene has shown consistent evidence of involvement in MS when family-based analyses were conducted. Furthermore, several clinical reports have suggested that the APOE-4 allele may be associated with more-severe disease and faster progression of disability. To thoroughly examine the role of APOE in MS, we genotyped its functional alleles, as well as seven single-nucleotide polymorphisms (SNPs) located primarily within 13 kb of APOE, in a data set of 398 families. Using family-based association analysis, we found statistically significant evidence that an SNP haplotype near APOE is associated with MS susceptibility (P=.005). An analysis of disease progression in 614 patients with MS from 379 families indicated that APOE-4 carriers are more likely to be affected with severe disease (P=.03), whereas a higher proportion of APOE-2 carriers exhibit a mild disease course (P=.02).

Apolipoprotein E and intellectual achievement

OBJECTIVES

To determine whether apolipoprotein E (apo E) genotype influences intellectual achievement in cognitively normal individuals.

DESIGN

Between 1994 and 1999 we performed apo E testing on 1,000 self-described cognitively normal residents of Maricopa County and detailed neuropsychological testing on a subset of 250.

SETTING

Tertiary care academic medical center.

PARTICIPANTS

Cognitively normal adults genotyped for apo E.

MEASUREMENTS

Measures of intellectual background included years of education and a demographically based estimate of intellectual capacity (demographic intellectual quotient (DIQ)). Measures of intellectual achievement, which included Wechsler Adult Intelligence Scale revised (WAIS-R), information (WAISI), and vocabulary (WAISV) scores, occupational intellectual requirements (OIR), and census-derived estimates of household income, were compared between apo E genetic subgroups while adjusting for intellectual background and demographic variables.

RESULTS

WAISI, WAISV, OIR, and income correlated with age, sex, education, and DIQ, but after controlling for these variables there were no clinically significant differences between apo E-e4 homozygotes and noncarriers on any measure.

CONCLUSIONS

No clinically significant differences between genotypes were observed for the effects of education and DIQ on WAISI, WAISV, OIR, or income, although a larger sample size would be required to exclude smaller, clinically insignificant differences.

Dementia with Lewy bodies and Alzheimer's disease

To investigate similarities and differences between Alzheimer's disease (AD) and dementia with Lewy bodies (DLB), we undertook a demographic analysis of 277 patients from the Kathleen Price Bryan Brain Bank with an antemortem diagnosis of probable AD. Patients with additional, possibly confounding clinical and pathologic diagnoses such as infarcts, hematomas, neoplasms, and other neurodegenerative disorders, were excluded from the analysis. Neuropathologically, AD alone was present in 192 subjects (69%), and DLB was found in 85 subjects (31%). All of the DLB cases had neuropathologic evidence of AD sufficient to meet CERAD criteria for a diagnosis of definite AD plus nigral Lewy bodies. Gender, apolipoprotein E (APOE) genotype, brain weight, age at death, duration of disease and Braak stage were compared between the two groups. Statistical analyses were performed using Fisher's exact test for comparisons of categorical data and Student's t-test for comparison of means for continuous outcomes. The proportion of males and females was balanced in the combined AD and DLB populations. There was a highly statistically significant increased frequency of APOE 3/4 in males with DLB (P = 0.007). We found higher brain weights in males with DLB versus males with AD (P = 0.012). AD was more frequent in females and DLB was more frequent in males (P = 0.019). Our findings with respect to age at death, duration of disease and Braak stage within diagnostic groups confirm previously reported findings. These data suggest that Lewy bodies are more common in males affected with dementia, especially those with the APOE 3/4 genotype.

The relationship of APOE genotype to cognitive functioning in older African-American and Caucasian community residents

OBJECTIVES

To determine whether cognitive decline associated with the apolipoprotein E (APOE) epsilon4 allele is different in older African Americans than it is in Caucasians.

DESIGN

Performance on a brief screen of cognitive functioning was examined at baseline (N = 1,891) and 4 years later (N = 1,389) to determine the extent to which the presence of APOE epsilon4 affected level of and change in performance, and whether this differed as a function of race, age, initial score, and change in score.

SETTING

Five adjacent counties in the Piedmont area of North Carolina.

PARTICIPANTS

In 1986, a stratified random household sample of community residents age 65 and older (n = 4,162; 54% African-American, 45% Caucasian, 1% other race) formed the Duke Established Populations for Epidemiologic Studies of the Elderly. Of those available at the sixth annual wave, 76% were genotyped, with 1,891 providing baseline data on this wave, and the available survivors (n = 1,389) providing longitudinal data 4 years later.

MEASUREMENTS

The Short Portable Mental Status Questionnaire (SPMSQ), a brief screen of cognitive functioning, was administered to all subjects on both occasions. We examined score at baseline and cognitive decline (i.e., increase of 2+ errors) at follow-up. Control measures included demographic characteristics, health behaviors, health and functional status, and medication use. APOE status was coded as epsilon4 present versus absent.

RESULTS

APOE epsilon4 was significantly and uniquely related to lower score at baseline and significantly increased the odds of cognitive decline by 59%. There was no statistically significant interaction between APOE epsilon4 and age, race, initial SPMSQ score, or SPMSQ score at follow-up.

CONCLUSION

APOE epsilon4 is modestly, if significantly, related to poorer cognitive functioning and to decline in cognitive functioning. No differences were found by age or race in this community representative sample.

Preclinical cognitive decline in late middle-aged asymptomatic apolipoprotein E-e4/4 homozygotes: a replication study

In a previous cross-sectional study of 100 asymptomatic individuals aged 49-69, we reported age-related decline in immediate and delayed memory that was steeper in apolipoprotein E (apoE)-e4/4 homozygotes than in members of other genetic subgroups. These findings were preliminarily based upon the statistical problem of multiple comparisons. We therefore sought to replicate these findings in a new cohort. From 1998 to 2000, 80 asymptomatic residents of Maricopa County, AZ were recruited through newspaper ads. 20 apoE-e4/4 homozygotes, 20 e3/4 heterozygotes, and 40 e4 noncarriers were matched (1:1:2) by age, gender, and years of education. All had normal neurologic and psychiatric examinations, including Folstein minimental status exam (MMSE) and Hamilton depression scale, and underwent a battery of neuropsychological tests identical to those in our previous study. The groups were well-matched for age (55.9+/-5.9 years), gender (60% women), and education (15.9+/-2.2 years), and were demographically similar to our previous cohort. Complex figure test recall was lower in e3/4 heterozygotes than noncarriers, but there was no significant difference between e4/4 homozygotes and noncarriers. There were no other significant differences in mean test scores between groups, but Wechsler adult intelligence scale-revised (WAIS-R) digit span showed a significant negative correlation with age in the e4/4 homozygote group relative to e4 noncarriers (p=0.008) as we had found in our previous study. In conclusion, we found a significant negative correlation of WAIS-R digit span with age in apoE-e4/4 homozygotes relative to e4 noncarriers in two separate cohorts, possibly reflecting an age-related effect on frontal lobe function in this genetic subgroup.

Gene identification in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in the elderly population. Three genes have been identified that cause the less common early-onset, familial cases of the disease: the amyloid precursor (APP) protein gene on chromosome 21, the presenilin 1 (PSEN1) gene on chromosome 14 and the presenilin 2 (PSEN2) gene on chromosome 1. Mutations in these genes account for << 2% of the total number of AD cases. More than 50% of the cases are late-onset and related to the apolipoprotein E (APOE) gene on chromosome 19. The apolipoprotein E locus is a susceptibility gene, with polymorphisms affecting both risk and age-of-onset of the disease. Intense efforts are underway to identify additional susceptibility genes and promising regions on chromosomes 6, 9, 10 and 12 have been identified through whole genome scans. In addition, the genetic basis of several other non-AD inherited dementias has been unravelled. Discovery of the genetically relevant genes will aid in the elucidation of the pathogenesis of AD. The high-throughput tools of pharmacogenomics for gene-to-function-to-target studies can provide a quicker means of monitoring how mutations and polymorphisms affect model systems' adaptations to the altered genes, possibly identifying signal transduction or biochemical pathways. This relevant information can then be used for drug target selection and pharmacogenetics.

Apolipoprotein E polymorphisms and age at first coronary artery bypass graft

Apolipoprotein E (apoE) polymorphisms are heritable determinants of total and low-density lipoprotein cholesterol. The impact of apoE4 genotypes on the severity of atherosclerosis has been debated; however, recent studies have identified a correlation between apoE4 genotype and atherosclerosis. We assessed the impact of apoE4 genotype on age at first coronary artery bypass graft (CABG), hypothesizing that patients with the apoE4 allele are predisposed to coronary artery disease and present earlier for coronary revascularization. We assessed individual apoE genotypes and age in 560 patients undergoing primary CABG, by using analysis of variance (ANOVA) and controlling for gender. Because of the small number of patients in individual genotype groups, we compared patients with one or more copies of the apoE4 allele with those having no copies of the allele, again controlling for gender. A comparison of patients with one or more copies of the apoE4 allele with patients without the allele showed an earlier age at first CABG for those with the allele (P: = 0.032). Gene-dose analysis was also significant (P: = 0.012); patients with two copies of the allele presented at 54.2 +/- 6.9 yr. We report that the apoE4 allele is linked to age at first CABG. Identifying at-risk individuals may help prevent atherosclerosis. Further study is needed to define the mechanism of this association, and to define which coronary intervention is appropriate, based on long-term outcome.

IMPLICATIONS

A correlation exists between apolipoprotein E (apoE) genotypes and the severity of atherosclerosis. We hypothesized that patients with the apoE4 allele are predisposed to coronary artery disease and present earlier for coronary artery bypass graft (CABG). Individuals with the apoE4 allele presented earlier for CABG, and the apoE4 allele is linked to age at first CABG.

Association of the apolipoprotein E gene with age-related macular degeneration: possible effect modification by family history, age, and gender

PURPOSE

Age-related macular degeneration (AMD) is a complex disorder affecting older adults in which genetic factors are likely to play a role. It has been previously suggested that the e4 allele of the apolipoprotein E (APOE) gene may have a protective effect on AMD risk and that the e2 allele may increase disease risk. The purpose of our study was to examine whether an independent data set would support the proposed role of APOE in AMD etiology.

METHODS

We compared AMD cases (n=230) to controls (n=372) with respect to APOE genotypes using c2 tests and logistic regression analysis. We also conducted separate analyses for familial (n=129) and sporadic (n=101) AMD cases since these groups may have a different disease etiology.

RESULTS

We did not find evidence for the risk-increasing effect attributed to the e2 allele in either familial or sporadic AMD. No evidence for a protective effect of the e4 allele was obtained for sporadic AMD. The age- and sex-adjusted odds ratio (OR) for e4 carriers among familial AMD cases compared to controls was 0.66 (95% confidence interval: 0.38-1.12, p=0.13). In the subgroup of individuals younger than 70 years of age, an OR of 0.24 (95% confidence interval: 0.08-0.72, p=0.004) was obtained.

CONCLUSIONS

Our data modestly support a protective effect of the APOE-e4 allele on AMD risk, but emphasize the need to investigate more thoroughly whether the effect could be restricted to cases with a family history of AMD and whether it varies across age and sex groups.

Identification of novel genes in late-onset Alzheimer's disease

Four genes affecting Alzheimer's Disease (AD)(AP, PS1, PS2, and APOE) have been identified and a fifth potential gene localized to chromosome 12. Collectively, these genes explain at most half of the genetic effect in AD. Understanding the genetics of AD is critical to developing new treatments. The quest to find the remaining AD genes led us to undertake a large genomic screen using over 466 families (730 affected sibpairs) in late-onset AD. In conjunction with this increase in power, we initiated several novel approaches to identify potential AD-related genes. This included stratification of the data into an autopsy-confirmed subset of 199 AD families. Each of these targeted analyses resulted in the identification of novel regions containing potential AD genetic risk factors. Our most significant finding was on chromosome 9 in the autopsy-confirmed subset where we obtained an MLS of 4.31. These approaches, together with new methodologies such as conditional linkage analysis, generalized family-based association tests (PDT), and a new generation of genetic markers (SNPs), opens the door for additional AD gene discovery. Such strategies are necessary if we are to understand the subtle and complex threads that, woven together, create the intricate tapestry of AD.

Genotypes and Phenotypes for Apolipoprotein E and Alzheimer Disease in the Honolulu-Asia Aging Study

Background: The utility of apolipoprotein E (ApoE) type as an indicator of genetic susceptibility to Alzheimer disease (AD) depends on the reliability of typing. Although ApoE protein isoform phenotyping is generally assumed equivalent to genotyping from DNA, phenotype-genotype differences have been reported.

Methods: ApoE genotype and phenotype results were examined for 3564 older (ages 71–93 years) Japanese-American male participants of the Honolulu-Asia Aging Study, an ongoing population-based study of aging and dementia.

Results: Both methods demonstrated similar associations of ApoE type with AD: a direct association with ApoE4 and a less dramatic inverse association ApoE2. Advanced age did not appear to influence the ApoE4-AD association. The association with AD among ApoE4 homozygotes [odds ratio (OR) = 14.7] was higher than expected based on an observed OR of 2.0 in heterozygotes. Phenotype-genotype nonconcordance was more frequent for ApoE2 than for ApoE4. The ApoE2 phenotype occurred at a frequency of 7.9% vs a genotype frequency of 4.9%, corresponding to a probability of 56% that an individual with ApoE2 phenotype had the same genotype.

Conclusions: Whereas E4 and E2 phenotypes and genotypes were comparably associated with AD, neither method would be expected to substantially improve the efficiency of case finding in the context of population screening beyond prediction based on age and education. Nonconcordance of phenotype and genotype was substantial for E2 and modest for E4 in this population. The ApoE4-AD association was independent of age.

Genotypes and phenotypes for apolipoprotein E and Alzheimer disease in the Honolulu-Asia aging study

BACKGROUND

The utility of apolipoprotein E (ApoE) type as an indicator of genetic susceptibility to Alzheimer disease (AD) depends on the reliability of typing. Although ApoE protein isoform phenotyping is generally assumed equivalent to genotyping from DNA, phenotype-genotype differences have been reported.

METHODS

ApoE genotype and phenotype results were examined for 3564 older (ages 71-93 years) Japanese-American male participants of the Honolulu-Asia Aging Study, an ongoing population-based study of aging and dementia.

RESULTS

Both methods demonstrated similar associations of ApoE type with AD: a direct association with ApoE4 and a less dramatic inverse association ApoE2. Advanced age did not appear to influence the ApoE4-AD association. The association with AD among ApoE4 homozygotes [odds ratio (OR) = 14.7] was higher than expected based on an observed OR of 2.0 in heterozygotes. Phenotype-genotype nonconcordance was more frequent for ApoE2 than for ApoE4. The ApoE2 phenotype occurred at a frequency of 7.9% vs a genotype frequency of 4.9%, corresponding to a probability of 56% that an individual with ApoE2 phenotype had the same genotype.

CONCLUSIONS

Whereas E4 and E2 phenotypes and genotypes were comparably associated with AD, neither method would be expected to substantially improve the efficiency of case finding in the context of population screening beyond prediction based on age and education. Nonconcordance of phenotype and genotype was substantial for E2 and modest for E4 in this population. The ApoE4-AD association was independent of age.

Apolipoprotein E and Alzheimer disease: an update on genetic and functional analyses

Exceptional advances have been made in understanding the genetics of how common polymorphisms of the apolipoprotein E gene influence the risk and age of onset of Alzheimer disease (AD). The major genetic susceptibility locus for the common forms of AD, there are 3 common alleles, designated epsilon2, epsilon3, and epsilon4. The inheritance of each dose of APOE4 increases the risk of disease and decreases the age of onset; conversely, the APOE2 allele appears to be protective, by lowering the risk of disease and increasing the age of onset. Testing for the APOE4 allele can be a clinically useful tool in the early diagnosis of cognitively impaired patients suspected of having AD. The APOE4 allele also negatively influences functional recovery following a variety of brain insults. What remains in the study of apolipoprotein E is an explanation of how minor changes in a protein can produce such striking differences in risk and age of onset. In vitro and animal model studies strongly suggest that brain apolipoprotein E is a multifunctional molecule, with potential roles in amyloid deposition and clearance, microtubule stability, intracellular signaling, immune modulation, glucose metabolism, oxidative stress, and other cellular processes. While the relevance of these proposed functions to the etiology of AD remains a mystery, these and other hypotheses will be tested as the field of apoE neurobiology grows, adding relevant new data to the functions of apoE in health and in the pathogenic mechanisms leading to AD.

Patterns of brain activation in people at risk for Alzheimer's disease

BACKGROUND

The epsilon4 allele of the apolipoprotein E gene (APOE) is the chief known genetic risk factor for Alzheimer's disease, the most common cause of dementia late in life. To determine the relation between brain responses to tasks requiring memory and the genetic risk of Alzheimer's disease, we performed APOE genotyping and functional magnetic resonance imaging (MRI) of the brain in older persons with intact cognition.

METHODS

We studied 30 subjects (age, 47 to 82 years) who were neurologically normal, of whom 16 were carriers of the APOE epsilon4 allele and 14 were homozygous for the APOE epsilon3 allele. The mean age and level of education were similar in the two groups. Patterns of brain activation during functional MRI scanning were determined while subjects memorized and recalled unrelated pairs of words and while subjects rested between such periods. Memory was reassessed in 14 subjects two years later.

RESULTS

Both the magnitude and the extent of brain activation during memory-activation tasks in regions affected by Alzheimer's disease, including the left hippocampal, parietal, and prefrontal regions, were greater among the carriers of the APOE epsilon4 allele than among the carriers of the APOE epsilon3 allele. During periods of recall, the carriers of the APOE epsilon4 allele had a greater average increase in signal intensity in the hippocampal region (1.03 percent vs. 0.62 percent, P<0.001) and a greater mean (+/-SD) number of activated regions throughout the brain (15.9+/-6.2 vs. 9.4+/-5.5, P=0.005) than did carriers of the APOE epsilon3 allele. Longitudinal assessment after two years indicated that the degree of base-line brain activation correlated with degree of decline in memory.

CONCLUSIONS

Patterns of brain activation during tasks requiring memory differ depending on the genetic risk of Alzheimer's disease and may predict a subsequent decline in memory.

Lewy body and Alzheimer pathology in a family with the amyloid-beta precursor protein APP717 gene mutation

Mutations in the amyloid precursor protein (APP) gene cause one form of early onset familial Alzheimer's disease (AD). One such family has been studied genetically and neuropathologically and represents the basis of the present report. Four siblings with the APP717 Val to Ile mutation, aged 59, 65, 61 and 64 years, apolipoprotein E (APOE) genotyped 2,4 (first three) and 2,3 respectively, had severe AD, Braak stage VI with frequent neurofibrillary tangles in the primary visual cortex, Brodmann area 17. The first one also met McKeith criteria for the limbic stage of dementia with Lewy bodies but did not have substantia nigra Lewy bodies. The second two met McKeith criteria for the neocortical stage of dementia with Lewy bodies and both had substantia nigra Lewy bodies. The fourth had AD but no Lewy bodies. A cousin without the APP717 mutation who was APOE 3, 4, developed dementia at age 60 and died at age 75. She had severe cerebrovascular atherosclerosis, less severe AD, Braak stage V, with sparing of area 17. She also had Lewy bodies in the substantia nigra and in the cortex and met McKeith criteria for neocortical stage of dementia with Lewy bodies. Extrapyramidal features were present in all five. Lewy bodies have been described in 53% of reported autopsies on individuals with the APP717 Val to Ile mutation coincident with dementia and AD neuropathologic changes. These observations suggest an association between the chromosome 21 APP mutation and Lewy body formation, possibly mediated by other environmental or genetic factors.