alpha 1-Antichymotrypsin as a risk modifier for late-onset Alzheimer's disease in Japanese apolipoprotein E epsilon 4 allele carriers

Novel insights into presenilin 1 mutation associated with a distinctive dementia phenotype and cotton wool plaques

BACKGROUND

The mutations in the presenilin 1 gene (PSEN1) are the main cause of familial Alzheimer's disease. PSEN1 mutations affect amyloid-beta peptide production, which accumulates in the brain as senile plaque and cotton wool plaques (CWPs) and relates to other neurodegenerative disorders. Here we report the second case of the PSEN1 G266S mutation, which showed distinctive neuropathological features, including abundant CWPs. Lewy body pathology, and altered amyloid-beta production.

METHOD

Using the proband's samples, we performed genetic analysis of the PSEN1, APP, MAPT, and APOE genes, histopathological and immunohistochemical analysis of the brain tissue, and biochemical analysis of Aβ production in COS cells transfected with wild-type or mutant PSEN1.

RESULTS

The patient presented with memory loss, abnormal behavior, and visual hallucinations. Brain scans showed reduced blood flow, mild atrophy, and white matter lesions. Genetic analysis revealed a heterozygous mutation at codon 266 (G266S) of PSEN1 and polymorphism of MAPT (Q230R). The brain had many CWPs, severe cerebral amyloid angiopathy (CAA), senile plaque, Lewy bodies, and neurites. Electron microscopy displayed myelinated fiber degeneration, mitochondrial damage, and amyloid fibrils in the white matter. The production level of Aβ42 in PSEN1 G266S-transfected cells significantly increased.

CONCLUSION

Our findings suggest that the PSEN1 G266S mutation may cause a heterogeneous clinical and pathological phenotype, influenced by other genetic or environmental factors.

Using game theory and decision decomposition to effectively discern and characterise bi-locus diseases

In order to gain insight into oligogenic disorders, understanding those involving bi-locus variant combinations appears to be key. In prior work, we showed that features at multiple biological scales can already be used to discriminate among two types, i.e. disorders involving true digenic and modifier combinations. The current study expands this machine learning work towards dual molecular diagnosis cases, providing a classifier able to effectively distinguish between these three types. To reach this goal and gain an in-depth understanding of the decision process, game theory and tree decomposition techniques are applied to random forest predictors to investigate the relevance of feature combinations in the prediction. A machine learning model with high discrimination capabilities was developed, effectively differentiating the three classes in a biologically meaningful manner. Combining prediction interpretation and statistical analysis, we propose a biologically meaningful characterization of each class relying on specific feature strengths. Figuring out how biological characteristics shift samples towards one of three classes provides clinically relevant insight into the underlying biological processes as well as the disease itself.

Epistasis in the risk of human neuropsychiatric disease

Neuropsychiatric disease represents the ideal class of disease to assess the role of epistasis, as more genes are expressed in the brain than in any other tissue. In this chapter, two well-studied neuropsychiatric diseases are examined, Alzheimer's disease (AD) and schizophrenia, which have been shown to have multiple and, often, replicated interactions that associate with clinical endpoints or related phenotypes. In each case, a single gene is represented in a plurality of epistatic interactions, apolipoprotein E (APOE) for AD and catechol-O-methyltransferase for schizophrenia. Interestingly, of the two, only APOE has clear-cut and consistent evidence for a marginal association. Unraveling the underlying reasons is important in understanding both genetic etiology and architecture as well as how to use genetics to provide better personalized treatments.

Association between α1-antichymotrypsin signal peptide -15A/T polymorphism and the risk of Alzheimer's disease: a meta-analysis

No consensus has been recently reached at the relationship between the α1-antichymotrypsin (ACT) signal peptide -15A/T polymorphism and Alzheimer’s disease (AD) risk. Thus, our study aimed to better assess this association by performing a meta-analysis, including 4,212 cases and 4,039 controls from 29 studies. Odds ratios (ORs) with the 95% confidence interval (CI) were used to assess the strength of relationship between ACT -15A/T polymorphism and AD risk. Overall, a borderline statistically significant association was detected under recessive model comparison in all subjects (AA vs. AT+TT: OR 1.12, 95% CI 1.01-1.25, P = 0.04). But in subgroup analysis by ethnicity, no significant association was found in Caucasians, Asians, or Africans. Moreover, after exclusion of one study which affect the heterogeneity, the ACT A allele and AA genotype were statistically associated with late-onset AD (LOAD) risk (AA vs. TT: OR 1.25, 95% CI 1.06-1.48, P = 0.007, A vs. T: OR 1.12, 95% CI 1.03-1.21, P = 0.008), especially in Caucasians. In conclusion, our study suggests that the common α1-antichymotrypsin signal peptide -15A/T polymorphism may not be a major risk factor for AD. However, the polymorphism is capable of increasing LOAD risk.

Beta-defensins and Crohn's disease: confusion from counting copies

Recent research has suggested that a family of antimicrobial and inflammatory molecules, called beta-defensins, are involved in the etiology of Crohn's disease. In this issue, Bentley and colleagues provide data that disagree with previous studies. They show that the beta-defensins that are copy number polymorphic have, on average, higher genomic copy number in patients when compared with healthy controls. This editorial places these new data in the context of previous research on the genetics of beta-defensin copy number polymorphism and association with Crohn's disease. It also suggests a path allowing this research area to move forward with confidence.

A SNP in the ACT gene associated with astrocytosis and rapid cognitive decline in AD

There is biochemical and animal model evidence supporting a pathological role of the ACT gene in AD. However, direct genetic evidence remains controversial and has been mostly limited to individual single nucleotide polymorphism (SNP) analysis. To resolve this apparent conflict we have used a high-density ACT SNP map, constructed haplotypes and explored correlations with phenotype. SNPs were identified by sequencing and used to construct haplotypes in 668 AD patients and 419 controls and a case-control association study was performed. Five SNPs, comprising five common haplotypes, represented 93% of ACT gene variation. Although no single SNP or haplotype was associated with AD status, a SNP in intron 2 was associated with later onset and more rapid cognitive decline (P=0.04). This SNP was both individually associated with severe astrocytosis (P=0.004) in AD patients and when combined with the signal sequence SNP (P=0.002). This suggests that astrocytosis may have a protective function for a limited period in some patients. These SNP associations either support a direct role for the ACT gene, in AD pathology or alternatively reflect linkage with polymorphisms in other genes nearby.

Meta-analysis of genetic variability in the beta-amyloid production, aggregation and degradation metabolic pathways and the risk of Alzheimer's disease

BACKGROUND

Variants in genes encoding enzymes involved in production, aggregation or degradation of beta-amyloid are potential risk factors for sporadic Alzheimer's disease (AD).

METHODS

Meta-analyses on AD association with BACE1 exon 5, BACE1 intron 5, FE65 intron 13, CYP46 intron 2, alpha(1)-antichymotrypsine Ala17Thr, bleomycin hydrolase I443V, lectin-like oxidized low-density lipoprotein receptor (OLR1) 3'-UTR (+1071) and (+1073), and very-low-density lipoprotein receptor (VLDLR) 5'-UTR (CGG-repeat) polymorphisms.

RESULTS

In BACE1 exon 5, genotype CC+CT acts as a protective factor in Apolipoprotein E (ApoE) epsilon 4 carriers [odds ratio (OR) = 0.57; 95% confidence interval (CI): 0.38-0.88], and as a risk factor in ApoE epsilon 4 non-carriers (OR = 1.33; 95% CI: 1.00-1.78). OLR1 3'-UTR (+1073) allele C is associated with increased risk (OR = 1.23; 95% CI: 1.01-1.50). VLDLR 5'-UTR genotype 2 is associated with increased risk (OR = 1.70; 95% CI: 1.09-2.63) in the Asian population and is protective (OR = 0.48; 95% CI: 0.26-0.86) in the non-Asian population. Other studied polymorphisms are not associated with AD.

CONCLUSIONS

The overall impact on AD risk of the genes for which meta-analyses are now available is rather limited. Additional meta-analyses of other different genes encoding for A beta production, aggregation and degradation mediators might help in determining the risk profile for AD.

A novel alternative splice variant of nicastrin and its implication in Alzheimer disease

Nicastrin interacts with gamma-secretase complex components predominantly via the N-terminal third of the transmembrane domain. The authentic transmembrane domain is critically required for the interaction with gamma-secretase complex components and for formation of an active gamma-secretase complex. In this study, we have identified a novel alternatively spliced transcript of nicastrin in human brain tissue. This transcript (NCSTN-DeltaE16) lacks exon 16 of nicastrin mRNA, which leads to deletion of 71 amino acids just upstream of its transmembrane domain. Its expression pattern was analyzed in the hippocampus of patients with pathologically diagnosed Alzheimer disease (cases) and non-Alzheimer dementia (controls). In patients with the APOE-epsilon4 allele, the frequency of Alzheimer disease appeared to be increased in the NCSTN-DeltaE16-positive group, but the association was not statistically significant. In conclusion, the expression of NCSTN-DeltaE16 transcript may confer some additional risk for developing Alzheimer disease beyond the risk due to ApoE-epsilon4 allele. Further investigation in larger scale population would be necessary to address its potential implication in Alzheimer disease.

Alpha-1-antichymotrypsin (ACT or SERPINA3) polymorphism may affect age-at-onset and disease duration of Alzheimer's disease

In addition to genetic effects on disease risk, age-at-onset (AAO) of Alzheimer's disease (AD) is also genetically controlled. Using AAO as a covariate, a linkage signal for AD has been detected on chromosome 14q32 near the alpha1-antichymotrypsin (ACT) gene. Previously, a signal peptide polymorphism (codon -17A>T) in the ACT gene has been suggested to affect AD risk, but with inconsistent findings. Given that a linkage signal for AAO has been detected near ACT, we hypothesized that ACT genetic variation affects AAO rather than disease risk and this may explain the previous inconsistent findings between ACT genetic variation and AD risk. We examined the impact of the ACT signal peptide polymorphism on mean AAO in 909 AD cases. The ACT polymorphism was significantly associated with AAO and this effect was independent of the APOE polymorphism. Mean AAO among ACT/AA homozygotes was significantly lower than that in the combined AT+TT genotype group (p = 0.019) and this difference was confined to male AD patients (p = 0.002). Among male AD patients, the ACT/AA genotype was also associated with shorter disease duration before death as compared to the ACT/AT+TT genotypes (p = 0.012). These data suggest that the ACT gene may affect AAO and disease duration of AD.

Modifier Genes and Oligogenic Disease

It is now increasingly apparent that modifier genes have a considerable role to play in phenotypic variations of single-gene disorders. Intrafamilial variations, altered penetrance, and altered severity are now common features of single gene disorders because of the involvement of several genes in the expression of the disease phenotype. Oligogenic disorders occur because of a second gene modifying the action of a dominant gene. It is now certain that cancer occurs due to the action of the environment acting in combination with several genes. Although modifier genes make it impossible to predict phenotype from the genotype and cause considerable difficulties in genetic counseling, they have their uses. In the future, it is hoped that modifier genes will allow us to understand cell and protein interactions and thus allow us to understand the pathogenesis of disease.

[ACT/AA polymorphism could duplicate the APOE*epsilon4-associated Alzheimer's disease risk]

BACKGROUND AND OBJECTIVE

The association between the presence of the allele APOE*epsilon4 (apolipoprotein E) and sporadic Alzheimer disease (AD) has been long established. However, the possible influence of other genetic factors is still under debate. This study investigated the role of the a 1-antichymotrypsin (ACT) gene as a susceptibility factor for developing late-onset AD in the population of Navarra.

PATIENTS AND METHODS

The study group included 98 patients with late-onset AD and 188 control individuals 70-71 years of age. APOE*epsilon2,*epsilon3,*epsilon4 and ACT codon -17*A,*T polymorphisms were analyzed by PCR-RFLP. Statistical analyses were performed determining the chi-square test, using 2 x 2 contingency tables and logistic regression to calculate odds ratios.

RESULTS

APOE*epsilon4 allele frequency was significantly higher in AD patients than in controls (odds ratio [OR] = 3.02; 95% confidence interval [CI], 1.59-5.73; p < 0.001 in heterozygous carriers, and OR = 9.40; 95% CI, 1.84-64.43; p = 0.001 in homozygous individuals). We found no significant differences in the distribution of ACT polymorphisms between AD cases and controls. However, APOE*epsilon4 carriers had a 2.5-fold increased risk of developing AD in the presence of the ACT/AA genotype (OR = 10.13; 95% CI, 1.98-97.81; p < 0.001). The risk difference, however, did not reach statistical significance (p = 0.271).

CONCLUSIONS

APOE*epsilon4 heterozygous and homozygous carriers have a 3 and 9 times higher risk, respectively, of developing AD. We could not demonstrate an effect of ACT polymorphisms as a independent risk factor for this disease; however, the ACT/AA genotype seems to act as an additional susceptibility factor, duplicating the APOE*epsilon4-associated AD risk.

Amyloid precursor protein (APP) and the biology of proteolytic processing: relevance to Alzheimer's disease

The processing of amyloid precursor protein (APP) generates amyloid-beta (Abeta) peptides 1-40 and 1-42. The latter is neurotoxic and its accumulation results in amyloid fibril formation and the generation of senile plaques, the hallmark of Alzheimer's disease (AD). Whilst there has been considerable progress made in understanding the generation of Abeta by alpha-, beta- and gamma-secretase activity on APP, recently enzymes involved in the degradation of Abeta have been identified including neprilysin and insulin-degrading enzyme (IDE). We review the pathways involved in proteolytic processing of APP and discuss the potential implications of aberrant proteolysis on neurodegeneration. It is conceivable that single nucleotide polymorphisms (SNPs) in the regulatory regions of genes in these proteolytic cascades, which alter their expression, could contribute to some of the age-related changes seen in AD.

Causative and susceptibility genes for Alzheimer's disease: a review

Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.

Plasma and cerebrospinal fluid alpha1-antichymotrypsin levels in Alzheimer's disease: correlation with cognitive impairment

alpha-1-Antichymotrypsin (ACT) is present in neuritic plaques in which it participates in the inflammatory cascade of Alzheimer's disease (AD). Reports of blood ACT levels in AD, and its usefulness as a disease biomarker, have been conflicting. In an effort to clarify this, we measured plasma ACT levels in 516 white subjects including 359 subjects with probable or possible AD, 44 subjects with other late-life dementias, and 113 nondemented people. Subjects with systemic inflammatory diseases or who were taking antiinflammatory medications were excluded. All patients underwent extensive medical and detailed neuropsychological examinations at the time their blood was drawn. We found that plasma ACT levels were elevated in AD patients compared with the control group (p = 0.01) and were associated with severity of AD dementia; there was a negative association with the Mattis Dementia Rating Scale (a global measure of cognition) and a positive association with the Clinical Dementia Rating Scale (a global functional assessment). These relationships remained significant after controlling for demographic and genetic variables. When AD subjects were stratified into subgroups by dementia severity, matched by age, education, and gender, increased serum ACT correlated with Clinical Dementia Rating Scale (p = 0.0041) or Mattis Dementia Rating Scale (p = 0.0031) scores. ACT measurements in cerebrospinal fluid from an additional 34 AD cases and 16 controls showed elevated levels (p = 0.02) in AD. There was a negative correlation (p = 0.037) between cerebrospinal fluid ACT levels and clinical severity as measured by the Mini-Mental State Examination. Our results demonstrate that peripheral ACT levels are elevated in AD, but not in dementias other than AD, and they increase with progression of AD dementia. Although not useful as a diagnostic biomarker, ACT may reflect disease severity and may be helpful as a within subject biomarker in interventions (particularly with antiinflammatory agents) directed at slowing or halting progression of disease.

Apolipoprotein E and alpha-1-antichymotrypsin genotypes do not predict time to psychosis in Alzheimer's disease

Psychotic symptoms occurring in Alzheimer's disease (AD + psychosis, AD + P) are a marker for a more rapidly deteriorating phenotype. We have developed a polygenic model of AD + P risk, conditioned on the presence of AD. Whether risk genes for AD itself contribute to AD + P risk is not established, although our model predicts they will not. The most important identified genetic determinant of sporadic, late-onset AD is the apolipoprotein E epsilon 4 allele (APOE4). The effect of APOE4 on AD phenotype is to reduce the age of onset of AD. Prior studies examining the association of APOE4 with AD + P have reported conflicting results. However, no prior studies have examined if APOE4 reduces time to onset of psychosis in AD. The objective of this study was to examine the effect of APOE4 and alpha1-antichymotrypsin/AA (ACT/AA) genotypes on time to psychosis onset in subjects with AD. A longitudinal study of psychosis incidence in 316 subjects with AD with no history of current or prior psychotic symptoms at entry was undertaken. APOE and ACT genotyping was conducted per established protocols. Data were analyzed by survival analysis and Cox proportional hazards models. There were no significant associations of APOE or ACT genotypes with time to psychosis onset and no significant interaction of these genotypes with time to psychosis onset. There remained no significant associations after covarying for age, age of AD onset, degree of cognitive impairment, gender, race, and education. This is the first study to examine the genetic prediction of psychosis onset in AD. The findings support the hypothesis that these two genetic determinants of AD risk do not contribute to the risk of development of psychotic symptoms in AD.

Molecular evidence of presenilin 1 mutation in familial early onset dementia

Early onset familial Alzheimer disease (FAD) has been associated with mutations in three genes, of which presenilin 1 (PSEN1) mutations are the most frequent. We reported previously a variant form of FAD, due to deletion of exon 9 of PSEN1, with spastic paralysis and rigidity. We describe a novel PSEN1 mutation in a family of Japanese origin with six affected individuals of both genders in two generations. The disease is characterized by presenile dementia, which is preceded by spastic paraparesis and apraxia. This mutation, which is predicted to cause a missense substitution of serine for glycine, occurred at codon 266 in exon 8 of PSEN1. The mutation was not found in 200 controls and 200 sporadic AD patients. On this basis alone, it seems this mutation is pathogenic. Our findings provide a new clue to the etiology of the familial early onset dementia.

Gene dose effect of the APOE-epsilon4 allele on plasma HDL cholesterol level in patients with Alzheimer's disease

It has been reported that decreased serum high density lipoprotein (HDL) cholesterol level is related with severity of Alzheimer's disease (AD). Here, 82 patients with AD and 40 non-demented individuals were examined to determine how the APOE-epsilon4 allele modifies plasma cholesterol fractions. In adjusting for age, sex and plasma albumin level, plasma HDL cholesterol level was inversely correlated with the APOE-epsilon4 dose only in the patients (P = 0.0048), while plasma low density lipoprotein (LDL) cholesterol level tended to be correlated with the APOE-epsilon4 dose in both groups, although this was not significant. The ratio of LDL to HDL cholesterol in the patients showed a similar correlation with the APOE-epsilon4 dose to that in the controls, and this correlation was evident (P = 0.0069) after putting all subjects into one group. However, neither HDL nor LDL cholesterol levels showed significant differences between the groups. These results indicated that the APOE-epsilon4 dose affects the composition of plasma cholesterol, and suggested that the genetic effect on plasma lipid metabolism could be distinctive in patients with AD.

Effect of cytokines, dexamethasone and the A/T-signal peptide polymorphism on the expression of alpha(1)-antichymotrypsin in astrocytes: significance for Alzheimer's disease

Proinflammatory cytokines and acute phase proteins, such as alpha(1)-antichymotrypsin, are over expressed in microglia and astrocytes in brain regions with abundant mature amyloid plaques, suggesting a glial cell-led brain acute phase response in the Alzheimer neuropathology. In this paper, we show that alpha(1)-antichymotrypsin gene expression in human astrocytes is elevated by interleukin-1 and interleukin-6, and further enhanced by glucocorticoid, while the homologous contrapsin gene in rat astrocytes is unaffected by these cytokines. These distinct gene regulation mechanisms might help to explain the differential susceptibility of humans and rodents to amyloid formation of the Alzheimer's type. In addition, we demonstrate that the alpha(1)-antichymotrypsin A-allele that encodes a different signal peptide and is a suggested risk factor for Alzheimer's disease gives rise to a reduced level of immature alpha(1)-antichymotrypsin in transfected cells. The physiological result would be an enhanced ability of the A-encoded alpha(1)-antichymotrypsin protein to become secreted and promote extracellular amyloid formation. We discuss our findings in terms of a model in which cytokine-induced alpha(1)-antichymotrypsin synthesis in astrocytes constitutes a specific inflammatory pathway that accelerates the development of Alzheimer's disease and could at least partly underlie the regional specificity and species restriction of the neuropathology.

Potential genetic markers of sporadic Alzheimer's dementia

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

No association between DLST gene and Alzheimer's disease or Wernicke-Korsakoff syndrome

Among many candidate genes for the genetically heterogeneous Alzheimer's disease (AD), only apolipoprotein E (ApoE) has been confirmed. Another candidate is the dihydrolipoyl succinyltransferase (DLST) gene, one of three components of thiamine-dependent mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC), because KGDHC activity is reported reduced in AD patients. Also characterized by reduced KGDHC activity is another neuropsychiatric disease, Wernicke-Korsakoff syndrome (WKS), which results from thiamine deficiency. Examination of specific DLST gene polymorphism in 247 Japanese AD patients, 53 alcoholic WKS patients, and 368 nondemented Japanese control subjects revealed no significant differences in DLST genotypes and failed to replicate the findings of earlier studies indicating an association between DLST gene polymorphism and AD.

Investigation of association of 13 polymorphisms in eight genes in southeastern African American Alzheimer disease patients as compared to age-matched controls

Alzheimer disease (AD) is an emotionally devastating and exceptionally costly disease. Apolipoprotein E (APOE) is a major risk factor gene for AD regardless of age of onset or family history. However, this association may not be as strong or consistent in ethnic groups such as African Americans, raising the possibility of other modifier gene(s). In a group of African American AD patients, a significantly increased risk of AD was associated with two E4 alleles (OR = 5.6; 95% CI = 1.5-21.0) or one E4 allele (OR = 2.5; 95% CI = 1.3-5.0) when compared to E3/E3 genotype, and there was a significant lowering of age of onset for affecteds with E4/E4 genotype as compared to one E2 allele (P = 0.02) or all others (P = 0.03). We also found a significant increase in age of onset with the -308 #2 (A) allele of TNF when compared to AD cases with no #2 allele. A significant increase in age was also demonstrated with the #2 allele (99 base pairs) of the microsatellite TNFa, located approximately 10.5 kb upstream of TNF. When these two alleles were combined with the TNF -238G (#1) allele to give a haplotype, the significant increase in age was still demonstrated. Polymorphisms in the APOE promoter and six other candidate genes did not appear to demonstrate any significant association with our African American AD patients. Our results confirm the established association of APOE4 to AD observed in several ethnic groups, including African Americans. In addition, TNF appears to have some modifying effect in AD, primarily on age of onset, or it could be in linkage disequilibrium with a modifier locus nearby.

Low density lipoprotein receptor-related protein gene polymorphisms and risk for late-onset Alzheimer's disease in a Japanese population

Low density lipoprotein (LDL) receptor-related protein (LRP) gene polymorphisms located in the 5' region and in exon 3, and the apolipoprotein E (APOE) genotype were determined in 100 Japanese patients affected by late-onset Alzheimer's disease (AD). We matched 246 controls for age and found no association between the polymorphism located in the 5' region of the LRP gene. The distribution of LRP exon 3 genotypes and alleles did not differ between AD and the control groups. However, the frequency of T allele in the Alzheimer's group having APOE-epsilon4 was lower than that in the control group having APOE-epsilon4, but it was only marginally significant (p = 0.022). Age of onset was significantly younger in the patients with CC genotype than those carrying the T allele (p = 0.03), and this trend was more evident among non-APOE-epsilon4 carriers (p = 0.008). These results support the possibility that ApoE and LRP may contribute to the development of AD.

Deficiency in mitochondrial aldehyde dehydrogenase increases the risk for late-onset Alzheimer's disease in the Japanese population

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) deficiency is caused by a mutant allele in the Mongoloids. To examine whether genetic constitutions affecting aldehyde metabolism influence the risk for late-onset Alzheimer's disease (LOAD), we performed a case-control study in the Japanese population on the deficiency in ALDH2 caused by the dominant-negative mutant allele of the ALDH2 gene (ALDH2*2). In a comparison of 447 patients with sex, age, and region matched nondemented controls, the genotype frequency carrying the ALDH2*2 allele was significantly higher in the patients than in the controls (48.1% vs 37.4%, P = 0.001). Logistic regression analysis indicates that carriage of the ALDH2*2 allele is an independent risk for LOAD of the epsilon4 allele of the apolipoprotein E gene (APOE-epsilon4) (P = 0.002). Moreover, the odds ratio for LOAD in carriers of the ALDH2*2 allele was almost twice that in noncarriers, irrespective of status with regard to the APOE-epsilon4 allele. Among patients homozygous for the APOE-epsilon4 allele, age at onset of LOAD was significantly lower in those with than without the ALDH2*2 allele. In addition, dosage of the ALDH2*2 allele significantly affected age at onset of patients homozygous for the APOE-epsilon4 allele. These results indicate that the ALDH2 deficiency is a risk for LOAD, synergistically acting with the APOE-epsilon4 allele.

Association of serum AACT levels and AACT signal polymorphism with late-onset Alzheimer's disease in Northern Ireland

alpha1-antichymotrypsin (AACT) is a serine protease inhibitor that has been associated with amyloid plaques in the brains of patients with Alzheimer's disease (AD). It has been reported that AACT serum levels are higher in AD patients than in age and sex matched controls. In addition, polymorphisms in the signal peptide and 5' of the AACT gene have been reported to increase the risk of developing AD. Serum AACT has also been suggested to be associated with cognitive decline in elderly subjects. Our objective was to investigate whether a relationship existed between serum AACT levels, AACT genotypes and risk for AD in a case control association study using 108 clinically well defined late onset AD cases and 108 age and sex matched controls from Northern Ireland. We also wished to determine whether higher serum AACT affected levels of cognition as had been previously reported. Serum AACT levels were found to be significantly raised in cases compared to controls (t=3.8, df=209, p<0.001). However, we detected no relationship between serum AACT levels and cognitive decline. We report allelic association of the AACT signal polymorphism with AD (chi(2)=3.70, df=1, p=0.04) but we failed to show any correlation between AACT serum levels and genotype.

Alzheimer's disease

This article reviews the clinical and neuropathological features of Alzheimer's disease, its known genetic and non-genetic risk factors, procedures used to make the diagnosis and rule out other reversible and non-reversible forms of dementia, and the treatment strategies used to help patients and their families cope with the problem. In addition, it considers how neuroimaging techniques promise to characterize the brain changes which precede the onset of cognitive impairment in persons at risk for Alzheimer's disease and identify treatments to prevent the onset of dementia.

Recent advances in dementia research in Japan: Alzheimer-type dementia

In a previous article, recent reports by Japanese researchers on non-Alzheimer-type degenerative dementias were reviewed. In the present article, recent Japanese reports on Alzheimer-type dementia (ATD) are reviewed. Alzheimer-type dementia has received great attention and has been studied from various viewpoints in Japan as well as in Europe and the Americas. In Japan, although it was believed that vascular dementia was the most frequent dementia in the elderly, ATD has recently been shown to be the most predominant type of dementia. Such a great number of papers on ATD have been reported in Japan that mainly the clinical, neuropathological, biochemical and molecular biological research papers alone are reviewed here.

Genetic risk factors in Alzheimer's disease

Following a brief introduction and discussion of the pathological features of Alzheimer's disease, the main emphasis of this review article will be the genetic factors that have been implicated in this disease. These can be divided into two main categories. First, the three genes in which mutations are known to result in early onset autosomal dominant familial Alzheimer's disease will be discussed. These are well characterised but account for only a small proportion of Alzheimer's disease cases. Late onset, sporadic Alzheimer's disease is more common and evidence suggests that there is a genetic component to this type of disease. A number of genetic risk factors have been implicated that might increase the risk of developing sporadic disease. Many of these are controversial and studies have shown conflicting results, which are discussed in this section. Finally, a brief discussion of some of the mechanisms suggested to play a role in the pathogenesis of Alzheimer's disease is included. It is hoped that this will show why particular genes have been implicated in Alzheimer's disease and how they might be able to influence the development of the disease.

Genetic association of two chromosome 14 genes (presenilin 1 and alpha 1-antichymotrypsin) with Alzheimer's disease

We have investigated the association of two candidate genes on chromosome 14, presenilin 1 (PS1) and alpha1-antichymotrypsin (ACT), with the risk of sporadic Alzheimer's disease (AD) by using 427 AD cases and 250 controls. The frequency of the ACT*A allele was significantly higher in cases than controls (0.550 vs 0.466). The stratification of the ACT data by PS1 genotypes showed that the risk associated with the ACT*A allele was confined to PS1*1 carriers only. The two-site haplotype data for PS1 and ACT showed that the A1 haplotype, carrying the ACT*A and PS1*1 alleles, was more frequent in cases than controls (0.310 vs 0.251), whereas the frequency of the T2 haplotype, carrying the ACT*T and PS1*2 alleles, was lower in cases than controls (0.177 vs 0.237). These data indicate a possible synergistic effect of these two loci on the risk of AD.

Association of alpha1-antichymotrypsin polymorphism with cerebral amyloid angiopathy

In search of genetic risk factors of sporadic cerebral amyloid angiopathy (CAA), we investigated the association of a polymorphism in the signal peptide sequence of alpha1-antichymotrypsin (ACT) with the severity of CAA in 155 autopsy cases of the elderly, including 48 patients with Alzheimer's disease. In the total cases, there was no significant association of the ACT genotypes (AA, AT, and TT) with the severity of CAA. Within the Alzheimer's disease group, however, a significant correlation was found between the ACT A allele frequency and the severity of CAA.

Genetic association studies between Alzheimer's disease and two polymorphisms in the low density lipoprotein receptor-related protein gene

The E*4 allele of apolipoprotein E (APOE) is a major risk factor for Alzheimer's disease (AD) but the underlying mechanism is unknown. The low density lipoprotein receptor-related protein (LRP) is directly involved in APOE metabolism and therefore may alter the risk of AD associated with APOE. Two common polymorphisms, a tetranucleotide repeat in the 5'-region and a same-sense mutation in exon 3, are present in the LRP gene. Three studies have reported conflicting association of the tetranucleotide polymorphism with AD. The only study of the exon 3 polymorphism found a significant association with AD. In this study we examined the association of these two LRP polymorphisms with sporadic late-onset AD. No significant association was observed between the tetranucleotide polymorphism and AD. While the overall genotype and allele frequencies for the LRP exon 3 polymorphism were comparable between AD cases and controls, the frequency of the TT genotype was significantly higher in controls than AD (5.7% vs. 2.5%; P < 0.01). Stratification of the data by APOE genotypes indicated that the protective effect associated with the TT genotype was confined to APOE*4 carriers. Although the effect of the exon 3 polymorphism in our sample is small compared to the previous study, this warrants additional studies to confirm this putative association.