Absence of association of alpha1-antichymotrypsin polymorphisms with Alzheimer's disease: a report on autopsy-confirmed cases

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.

Complement activation as a biomarker for Alzheimer's disease

There is increasing evidence from genetic, immunohistochemical, proteomic and epidemiological studies as well as in model systems that complement activation has an important role in the pathogenesis of Alzheimer's disease (AD). The complement cascade is an essential element of the innate immune response. In the brain complement proteins are integral components of amyloid plaques and complement activation occurs at the earliest stage of the disease. The complement cascade has been implicated as a protective mechanism in the clearance of amyloid, and in a causal role through chronic activation of the inflammatory response. In this review we discuss the potential for complement activation to act as a biomarker for AD at several stages in the disease process. An accurate biomarker that has sufficient predictive, diagnostic and prognostic value would provide a significant opportunity to develop and test for effective novel therapies in the treatment of AD.

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.

[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.

Lack of association between alpha1-antichymotrypsin polymorphism and late-onset depressive disorder

Late-onset depressive disorder (LOD) has been thought to be associated with dementia. Recently, it was reported that the position-15 (alanine) polymorphism of the alpha1-antichymotrypsin gene (ACT*A) was a risk factor for Alzheimer's disease. We wondered whether the ACT*A allele frequency might be elevated in LOD. ACT genotyping was performed as described by Kamboh et al. (Kamboh, M.I., Sanghera D.K., Ferrell R.E., DeKosky, S.T., 1995. APO* E4-associated Alzheimer's disease risk is modified by alpha1-antichymotrypsin polymorphism. Nature Genetics 10, 486-488) in 153 patients with depressive disorders and 107 healthy controls. The patients were subdivided into those with early-onset and late-onset, using 50 years as the cut-off age. There was no statistically significant difference in the age of onset of depressive disorders according to the ACT genotype. There was also no significant association between early-/late-onset depressive disorders and the ACT genotype. In addition, there was no association between the apolipoprotein E epsilon 4 allele and the ACT genotype in LOD. Our results suggest that there is no association between the ACT*A allele and LOD.