No genetic association between alpha-2 macroglobulin I1000V polymorphism and Japanese sporadic Alzheimer's disease

Alpha 2-Macroglobulin Polymorphisms and Susceptibility to Alzheimer's Disease: A Comprehensive Meta-Analysis Based on 62 Studies

Background

The relationship between alpha 2-macroglobulin (A2M) gene and Alzheimer's disease (AD) has been widely studied across populations; however, the results are inconsistent.

Objective

This study aimed to evaluate the association of A2M gene with AD by the application of meta-analysis.

Methods

Relevant studies were identified by comprehensive searches. The quality of each study was assessed using the Newcastle-Ottawa Scale. Allele and genotype frequencies were extracted from each of the included studies. Odds ratio (OR) with corresponding 95% confidence intervals (CI) was calculated using a random-effects or fixed-effects model. The Cochran Q statistic and I2 metric was used to evaluate heterogeneity, and Egger's test and Funnel plot were used to assess publication bias.

Results

A total of 62 studies were identified and included in the current meta-analysis. The G allele of rs226380 reduced AD risk (OR: 0.64, 95% CI: 0.47-0.87, pFDR = 0.012), but carrier with the TT genotype was more likely to develop AD in Asian populations (OR: 1.56, 95% CI: 1.12-2.19, pFDR = 0.0135). The V allele of the A2M-I/V (rs669) increased susceptibility to AD in female population (OR, 95% CI: 2.15, 1.38-3.35, pFDR = 0.0024); however, the II genotype could be a protective factor in these populations (OR, 95% CI: 0.43, 0.26-0.73, pFDR = 0.003). Sensitivity analyses confirmed the reliability of the original results.

Conclusions

Existing evidence indicate that A2M single nucleotide polymorphisms (SNPs) may be associated with AD risk in sub-populations. Future studies with larger sample sizes will be necessary to confirm the results.

Influence of Alpha-2-Macroglobulin 5 bp I/D and Ile1000Val polymorphisms on the susceptibility of Alzheimer's disease: a systematic review and meta-analysis of 52 studies

Accumulating studies have evaluated the association of Alpha-2-Macroglobulin gene (A2M) 5 bp insertion/deletion (5 bp I/D, rs3832852) and Ile1000Val (rs669) polymorphisms with Alzheimer's disease (AD) risk, but the results remain inconclusive. To investigate whether these two polymorphisms facilitate the susceptibility to AD, we conducted a comprehensive systematic review and meta-analysis. Databases of PubMed, Embase, Web of Science, Medline, CNKI, and Google Scholar were searched to get the genetic association studies. All statistical analyses were conducted with Review Manager 5.2 and STATA11.0. Fifty-two articles were included in the final meta-analysis. We performed meta-analysis of 39 studies involving 8,267 cases and 7,932 controls for the 5 bp I/D polymorphism and 27 studies involving 6,585 cases and 6,637 controls for the Ile/Val polymorphism. Overall results did not show significant association between these two polymorphisms and AD risk in dominant, recessive, and multiplicative genetic models. On the stratification analyses by ethnicity and APOE ε4 status with genotypes of polymorphism sites, similar negative associations were found. The meta-analysis suggests that there is no enough evidence for associations of A2M gene polymorphisms (5 bp I/D, Ile1000Val) with AD risk at present, even after stratification by ethnicity and APOE ε4 with genotypes of polymorphism sites. However, due to the heterogeneity in the meta-analysis, the results should be interpreted with caution.

Candidate genes for late-onset Alzheimer's disease: Focus on chromosome 12

In recent years, there was an increasing interest on candidate genes may play an important role in the development of Alzheimer's disease (AD). Several genome wide screens have undertaken so far or expanded recently, and suggested a number of genomic areas that may contain novel susceptibility genes for AD, in particular most compelling have been the findings on chromosome 12. Polymorphisms in different susceptibility genes on chromosome 12 (A2M, LRP1, CP2 and OLR1) are now being suggested as possible genetic markers for increased risk of developing AD. However, many of these studies are controversial and have shown conflicting results. Thus far, the search for the chromosome 12 Alzheimer's gene must continue and there are several other genes in this region that we are looking at. In this article, we focused on the current knowledge of the genetics of familial late-onset and sporadic AD linked to the chromosome 12, and the future search for other candidate genes.

Current knowledge of chromosome 12 susceptibility genes for late-onset Alzheimer's disease

In the last decade, it has become more apparent the important role genes play in the development of late-onset Alzheimer's disease (AD). Great efforts, involving human genome scans and candidate gene studies, have been given towards identifying susceptibility genes for AD. A number of regions on different chromosomes have been reported to demonstrate linkage for AD. Of these, findings on chromosome 12 are some of the most compelling. Worldwide genetic association studies pre-dating and subsequent to recent linkage studies have identified and focused upon a number of genes that map to the areas of reported linkage on chromosome 12, however, analyses of those genes studied to date, on the whole, remain inconclusive and ambiguous. This paper reviews studies that have provided evidence of linkage for AD on chromosome 12 and in turn discusses the work conducted to date on candidate genes that have been identified and map to the chromosome 12 regions of interest.

Association of α2-macroglobulin polymorphisms and Alzheimer disease in Mainland Han Chinese

This study used case-control method to investigate roles of two alpha 2-macroglobulin (A2M) polymorphisms, a 5-bp insertion/deletion (A2M-I/D) and an A-->G substitution (A2M-A/G), in the development of sporadic Alzheimer disease (AD) in Mainland Han Chinese. Our results showed a trend of lower D-carrying genotype frequency in APOE-epsilon 4 carrying AD patients than in corresponding control subjects (chi(2)=3.67, p=0.055). The ID/AA genotype frequency was lower in AD patients comparing with controls (chi(2)=4.04, p=0.044). In AD patients, the G-carrying genotype frequency was significantly higher in APOE-epsilon 4 carrier subgroup than in APOE-epsilon 4 non-carriers (chi(2)=7.38, OR=2.99, 95% CI: 1.33-6.71, p=0.007). These results indicated that A2M-D allele was probably a weak AD protective factor, and there was a possible interaction of APOE-epsilon 4 and A2M-G alleles to increase AD risk in Mainland Han Chinese.

Alpha-2 macroglobulin I1000 V polymorphism in Chinese sporadic Alzheimer's disease and Parkinson's disease

Several lines of evidence have revealed some overlapping pathologies in Alzheimer's disease (AD) and Parkinson's disease (PD). Although the alpha-2 macroglobulin gene (A2M) might be a risk factor of these two neurodegenerative diseases, conclusions from different studies have remained conflicting. Here we studied the role of A2M I1000 V polymorphism in both AD and PD in a Chinese Han population. We found that the A2M I/V genotype is associated with both AD (odds ratio (OR)=2.55, 95% confidential interval (95% CI): 1.20-5.43, attributable fraction (AF)=13.65%) and PD (OR=3.03, 95% CI: 1.30-7.02, AF=16.51%). After classifying according to the age of onset, this association is only detected in early-onset AD patients (OR=3.96, 95% CI: 1.28-12.26) and late-onset PD patients (OR=2.61, 95% CI: 0.97-7.09). Therefore, we conclude that in our samples, the A2M I/V genotype might be a susceptibility variant, even with minor effect, for both sporadic AD and PD.

Alpha2-macroglobulin exon 24 (Val-1000-Ile) polymorphism is not associated with late-onset sporadic Alzheimer's dementia in the Hungarian population

Several lines of biochemical evidence support a role of alpha2-macroglobulin (A2M) in the pathogenesis of Alzheimer's dementia (AD). A2M participates in the general defence mechanism against proteinases and it is supposed to be involved in the degradation of beta-amyloid peptide (betaAP). Furthermore, A2M has been shown to reduce betaAP fibril formation, and it is upregulated in the acute-phase inflammatory response like the process occurring in the AD brain. The exon 18 splice acceptor deletion polymorphism and the exon 24 (Val-1000-Ile) GG genotype were reported to be associated with AD, but the results are contradictory. Since the Hungarian population is genetically distinct from the other European ethnic groups, we examined whether the risk for developing AD is increased in the A2M GG carriers. The interaction of apolipoprotein E (apoE) and A2M polymorphisms was also examined. The distribution of A2M genotypes and alleles in the entire data set was consistent with the previous negative observations in which A and G allelic frequencies were comparable in both groups (72% and 28% in the AD population, and 72% and 28% in the control population, respectively). The GG genotype was over-represented (14%) only in the apoE epsilon4 non-carrier subgroup of AD probands (7% in the control group), but the difference was not significant. Our data suggest that, although A2M has an important role in the AD-specific neurodegenerative process, its exon 24 Val-1000-Ile polymorphism is not likely to be associated with late-onset sporadic AD in the Hungarian population.