Genetic association of ?2-macroglobulin with Alzheimer's disease in a Finnish elderly population

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.

Distribution of Lewy-related pathology in the brain, spinal cord, and periphery: the population-based Vantaa 85 + study

Evolving evidence has supported the existence of two anatomically distinct Lewy-related pathology (LRP) types. Investigation of spinal cord and peripheral LRP can elucidate mechanisms of Lewy body disorders and origins of synuclein accumulation. Still, very few unselected studies have focused on LRP in these regions. Here we analysed LRP in spinal cord, dorsal root ganglion, and adrenal gland in the population-based Vantaa 85 + study, including every ≥ 85 years old citizen living in the city of Vantaa in 1991 (n = 601). Samples from spinal cord (C6-7, TH3-4, L3-4, S1-2) were available from 303, lumbar dorsal root ganglion from 219, and adrenal gland from 164 subjects. Semiquantitative scores of LRP were determined from immunohistochemically stained sections (anti-alpha-synuclein antibody 5G4). LRP in the ventral and dorsal horns of spinal cord, thoracic intermediolateral column, dorsal root ganglion and adrenal gland were compared with brain LRP, previously determined according to DLB Consortium criteria and by caudo-rostral versus amygdala-based LRP classification. Spinal LRP was found in 28% of the total population and in 61% of those who had LRP in the brain. Spinal cord LRP was found only in those subjects with LRP in the brain, and the quantity of spinal cord LRP was associated with the severity of brain LRP (p < 0.001). Unsupervised K-means analysis identified two cluster types of spinal and brain LRP corresponding to caudo-rostral and amygdala-based LRP types. The caudo-rostral LRP type exhibited more frequent and severe pathology in spinal cord, dorsal root ganglion and adrenal gland than the amygdala-based LRP type. Analysis of specific spinal cord regions showed that thoracic intermediolateral column and sacral dorsal horn were the most frequently affected regions in both LRP types. This population-based study on brain, spinal and peripheral LRP provides support to the concept of at least two distinct LRP types.

Primary Age‐Related Tauopathy (PART) in a Finnish Population‐Based Study of the Oldest Old (Vantaa 85+)

Aims

Few studies have investigated primary age‐related tauopathy (PART) in a population‐based setting. Here, we assessed its prevalence, genetic background, comorbidities and features of cognitive decline in an unselected elderly population.

Methods

The population‐based Vantaa 85+ study includes all 601 inhabitants of Vantaa aged ≥ 85 years in 1991. Neuropathological assessment was possible in 301. Dementia (DSM IIIR criteria) and Mini‐Mental State Examination (MMSE) scores were assessed at the baseline of the study and follow‐ups. PART subjects were identified according to the criteria by Crary et al and were compared with subjects with mild and severe Alzheimer's disease (AD) neuropathological changes. The effects of other neuropathologies were taken into account using multivariate and sensitivity assays. Genetic analyses included APOE genotypes and 29 polymorphisms of the MAPT 3′ untranslated region (3′UTR region).

Results

The frequency of PART was 20% (n = 61/301, definite PART 5%). When PART subjects were compared with those with severe AD pathology, dementia was less common, its age at onset was higher and duration shorter. No such differences were seen when compared with those with milder AD pathology. However, both AD groups showed a steeper decline in MMSE scores in follow‐ups compared with PART. APOE ε4 frequency was lower, and APOE ε2 frequency higher in the PART group compared with each AD group. The detected nominally significant associations between PART and two MAPT 3′UTR polymorphisms and haplotypes did not survive Bonferroni correction.

Conclusions

PART is common among very elderly. PART subjects differ from individuals with AD‐type changes in the pattern of cognitive decline, associated genetic and neuropathological features.

Indomethacin Disrupts the Formation of β-Amyloid Plaques via an α2-Macroglobulin-Activating lrp1-Dependent Mechanism

Epidemiological studies have implied that the nonsteroidal anti-inflammatory drug (NSAID) indomethacin slows the development and progression of Alzheimer’s disease (AD). However, the underlying mechanisms are notably understudied. Using a chimeric mouse/human amyloid precursor protein (Mo/HuAPP695swe) and a mutant human presenilin 1 (PS1-dE9) (APP/PS1) expressing transgenic (Tg) mice and neuroblastoma (N) 2a cells as in vivo and in vitro models, we revealed the mechanisms of indomethacin in ameliorating the cognitive decline of AD. By screening AD-associated genes, we observed that a marked increase in the expression of α₂-macroglobulin (A2M) was markedly induced after treatment with indomethacin. Mechanistically, upregulation of A2M was caused by the inhibition of cyclooxygenase-2 (COX-2) and lipocalin-type prostaglandin D synthase (L-PGDS), which are responsible for the synthesis of prostaglandin (PG)H₂ and PGD₂, respectively. The reduction in PGD₂ levels induced by indomethacin alleviated the suppression of A2M expression through a PGD₂ receptor 2 (CRTH2)-dependent mechanism. Highly activated A2M not only disrupted the production and aggregation of β-amyloid protein (Aβ) but also induced Aβ efflux from the brain. More interestingly, indomethacin decreased the degradation of the A2M receptor, low-density lipoprotein receptor-related protein 1 (LRP1), which facilitated the brain efflux of Aβ. Through the aforementioned mechanisms, indomethacin ameliorated cognitive decline in APP/PS1 Tg mice by decreasing Aβ production and clearing Aβ from the brains of AD mice.

Lewy-related pathology exhibits two anatomically and genetically distinct progression patterns: a population-based study of Finns aged 85

According to a generally accepted concept Lewy-related pathology (LRP) follows hierarchical caudo-rostral progression. LRP is also frequently present concomitantly with Alzheimer’s disease (AD), and it has been hypothesized that AD-associated LRP forms a distinct type of α-synucleinopathy, where LRP originates in the amygdala. The frequency of distinct forms of LRP progression types has not been studied in a population-based setting. We investigated the distribution and progression of LRP and its relation to AD pathology and apolipoprotein (APOE) ε4 in a population-based sample of Finns aged over 85 years (N = 304). Samples from spinal cord to neocortical areas representing 11 anatomical sites without any hierarchical selection were analyzed immunohistochemically (α-synuclein antibody clone 5G4). LRP was present in 124 individuals (41%) and according to DLB Consortium guidelines 19 of them were categorized as brainstem, 10 amygdala-predominant, 41 limbic, and 43 diffuse neocortical type, whereas 11 could not be classified. To determine the LRP progression patterns, a systematic anatomical scoring was carried out by taking into account the densities of the semiquantitative LRP scores in each anatomic site. With this scoring 123 (99%) subjects could be classified into two progression pattern types: 67% showed caudo-rostral and 32% amygdala-based progression. The unsupervised statistical K-means cluster analysis was used as a supplementary test and supported the presence of two progression patterns and had a 90% overall concordance with the systematic anatomical scoring method. Severe Braak NFT stage, high CERAD score and APOE ε4 were significantly (all p < 0.00001) associated with amygdala-based, but not with caudo-rostral progression type (all p > 0.2). This population-based study demonstrates two distinct common LRP progression patterns in the very elderly population. The amygdala-based pattern was associated with APOE ε4 and AD pathology. The results confirm the previous progression hypotheses but also widen the concept of the AD-associated LRP.

Tau accumulation triggers STAT1-dependent memory deficits by suppressing NMDA receptor expression

Intracellular tau accumulation forming neurofibrillary tangles is hallmark pathology of Alzheimer's disease (AD), but how tau accumulation induces synapse impairment is elusive. By overexpressing human full-length wild-type tau (termed hTau) to mimic tau abnormality as seen in the brain of sporadic AD patients, we find that hTau accumulation activates JAK2 to phosphorylate STAT1 (signal transducer and activator of transcription 1) at Tyr701 leading to STAT1 dimerization, nuclear translocation, and its activation. STAT1 activation suppresses expression of N-methyl-D-aspartate receptors (NMDARs) through direct binding to the specific GAS element of GluN1, GluN2A, and GluN2B promoters, while knockdown of STAT1 by AAV-Cre in STAT1^flox/flox mice or expressing dominant negative Y701F-STAT1 efficiently rescues hTau-induced suppression of NMDAR expression with amelioration of synaptic functions and memory performance. These findings indicate that hTau accumulation impairs synaptic plasticity through JAK2/STAT1-induced suppression of NMDAR expression, revealing a novel mechanism for hTau-associated synapse and memory deficits.

Melatonin receptor type 1A gene linked to Alzheimer's disease in old age

Disruption of the circadian rhythms is a frequent preclinical and clinical manifestation of Alzheimer’s disease. Furthermore, it has been suggested that shift work is a risk factor for Alzheimer’s disease. Previously, we have reported association of intolerance to shift work (job-related exhaustion in shift workers) with a variant rs12506228A, which is situated close to melatonin receptor type 1A gene (MTNR1A) and linked to MTNR1A brain expression levels. Here, we studied association of that variant with clinical and neuropathological Alzheimer’s disease in a Finnish whole-population cohort Vantaa 85+ (n = 512, participants over 85 years) and two follow-up cohorts. Rs12506228A was associated with clinical Alzheimer’s disease (p = 0.000073). Analysis of post-mortem brain tissues showed association with higher amount of neurofibrillary tangles (p = 0.0039) and amyloid beta plaques (p = 0.0041). We then followed up the associations in two independent replication samples. Replication for the association with clinical Alzheimer’s disease was detected in Kuopio 75+ (p = 0.012, n = 574), but not in the younger case-control sample (n = 651 + 669). While melatonin has been established in regulation of circadian rhythms, an independent role has been also shown for neuroprotection and specifically for anti-amyloidogenic effects. Indeed, in vitro, RNAi mediated silencing of MTNR1A increased the amyloidogenic processing of amyloid precursor protein (APP) in neurons, whereas overexpression decreased it. Our findings suggest variation close to MTNR1A as a shared genetic risk factor for intolerance to shift work and Alzheimer’s disease in old age. The genetic associations are likely to be mediated by differences in MTNR1A expression, which, in turn, modulate APP metabolism.

C9orf72 hexanucleotide repeat length in older population: normal variation and effects on cognition

The hexanucleotide repeat expansion in C9orf72 is a common cause of amyotrophic lateral sclerosis/frontotemporal dementia and also rarely found in other psychiatric and neurodegenerative conditions. Alleles with >30 repeats are often considered an expansion, but the pathogenic repeat length threshold is still unclear. It is also unclear whether intermediate repeat length alleles (often defined either as 7-30 or 20-30 repeats) have clinically significant effects. We determined the C9orf72 repeat length distribution in 3142 older Finns (aged 60-104 years). The longest nonexpanded allele was 45 repeats. We found 7-45 repeats in 1036/3142 (33%) individuals, 20-45 repeats in 56/3142 (1.8%), 30-45 repeats in 12/3142 (0.38%), and expansion (>45 repeats) in 6/3142 (0.19%). There was no apparent clustering of neurodegenerative or psychiatric diseases in individuals with 30-45 repeats indicating that 30-45 repeats are not pathogenic. None of the 6 expansion carriers had a diagnosis of amyotrophic lateral sclerosis/frontotemporal dementia but 4 had a diagnosis of a neurodegenerative or psychiatric disease. Intermediate length alleles (categorized as 7-45 and 20-45 repeats) did not associate with Alzheimer's disease or cognitive impairment.

Prediction models for dementia and neuropathology in the oldest old: the Vantaa 85+ cohort study

Background

We developed multifactorial models for predicting incident dementia and brain pathology in the oldest old using the Vantaa 85+ cohort.

Methods

We included participants without dementia at baseline and at least 2 years of follow-up (N = 245) for dementia prediction or with autopsy data (N = 163) for pathology. A supervised machine learning method was used for model development, considering sociodemographic, cognitive, clinical, vascular, and lifestyle factors, as well as APOE genotype. Neuropathological assessments included β-amyloid, neurofibrillary tangles and neuritic plaques, cerebral amyloid angiopathy (CAA), macro- and microscopic infarcts, α-synuclein pathology, hippocampal sclerosis, and TDP-43.

Results

Prediction model performance was evaluated using AUC for 10 × 10-fold cross-validation. Overall AUCs were 0.73 for dementia, 0.64–0.68 for Alzheimer’s disease (AD)- or amyloid-related pathologies, 0.72 for macroinfarcts, and 0.61 for microinfarcts. Predictors for dementia were different from those in previous reports of younger populations; for example, age, sex, and vascular and lifestyle factors were not predictive. Predictors for dementia versus pathology were also different, because cognition and education predicted dementia but not AD- or amyloid-related pathologies. APOE genotype was most consistently present across all models. APOE alleles had a different impact: ε4 did not predict dementia, but it did predict all AD- or amyloid-related pathologies; ε2 predicted dementia, but it was protective against amyloid and neuropathological AD; and ε3ε3 was protective against dementia, neurofibrillary tangles, and CAA. Very few other factors were predictive of pathology.

Conclusions

Differences between predictors for dementia in younger old versus oldest old populations, as well as for dementia versus pathology, should be considered more carefully in future studies.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0450-3) contains supplementary material, which is available to authorized users.

Genetics of dementia in a Finnish cohort

Alzheimer's disease (AD) and frontotemporal dementia (FTD) are the two most common neurodegenerative dementias. Variants in APP, PSEN1 and PSEN2 are typically linked to early-onset AD, and several genetic risk loci are associated with late-onset AD. Inherited FTD can be caused by hexanucleotide expansions in C9orf72, or variants in GRN, MAPT or CHMP2B. Several other genes have also been linked to FTD or FTD with motor neuron disease. Here we describe a cohort of 60 Finnish families with possible inherited dementia. Our aim was to clarify the genetic background of dementia in this cohort by analysing both known dementia-associated genes (APOE, APP, C9ORF72, GRN, PSEN1 and PSEN2) and searching for rare or novel segregating variants with exome sequencing. C9orf72 repeat expansions were detected in 12 (20%) of the 60 families, including, in addition to FTD, a family with neuropathologically verified AD. Twelve families (10 with AD and 2 with FTD) with representative samples from affected and unaffected subjects and without C9orf72 expansions were selected for whole-exome sequencing. Exome sequencing did not reveal any variants that could be regarded unequivocally causative, but revealed potentially damaging variants in UNC13C and MARCH4.

Alzheimer risk loci and associated neuropathology in a population-based study (Vantaa 85+)

Objective

To test the association of distinct neuropathologic features of Alzheimer disease (AD) with risk loci identified in genome-wide association studies.

Methods

Vantaa 85+ is a population-based study that includes 601 participants aged ≥85 years, of which 256 were neuropathologically examined. We analyzed 29 AD risk loci in addition to APOE ε4, which was studied separately and used as a covariate. Genotyping was performed using a single nucleotide polymorphism (SNP) array (341 variants) and imputation (6,038 variants). Participants with Consortium to Establish a Registry for Alzheimer Disease (CERAD) (neuritic Aβ plaques) scores 0 (n = 65) vs score M + F (n = 171) and Braak (neurofibrillary tangle pathology) stages 0–II (n = 74) vs stages IV–VI (n = 119), and with capillary Aβ (CapAβ, n = 77) vs without (n = 179) were compared. Cerebral amyloid angiopathy (CAA) percentage was analyzed as a continuous variable.

Results

Altogether, 24 of the 29 loci were associated (at p < 0.05) with one or more AD-related neuropathologic features in either SNP array or imputation data. Fifteen loci associated with CERAD score, smallest p = 0.0002122, odds ratio (OR) 2.67 (1.58–4.49) at MEF2C locus. Fifteen loci associated with Braak stage, smallest p = 0.004372, OR 0.31 (0.14–0.69) at GAB2 locus. Twenty loci associated with CAA, smallest p = 7.17E-07, β 14.4 (8.88–20) at CR1 locus. Fifteen loci associated with CapAβ smallest p = 0.002594, OR 0.54 (0.37–0.81) at HLA-DRB1 locus. Certain loci associated with specific neuropathologic features. CASS4, CLU, and ZCWPW1 associated only with CAA, while TREM2 and HLA-DRB5 associated only with CapAβ.

Conclusions

AD risk loci differ in their association with neuropathologic features, and we show for the first time distinct risk loci for CAA and CapAβ.

Population-based analysis of pathological correlates of dementia in the oldest old

Objective

The aim of this study was to analyze brain pathologies which cause dementia in the oldest old population.

Methods

All 601 persons aged ≥85 years living in the city of Vantaa (Finland), on April 1st, 1991 formed the study population of the Vantaa85 +  study, 300 of whom were autopsied during follow‐up (79.5% females, mean age‐at‐death 92 ± 3.7 years). Alzheimer's disease (AD) pathology (tau and beta‐amyloid [Aβ]), cerebral amyloid angiopathy (CAA) and Lewy‐related pathologies were analyzed. Brain infarcts were categorized by size (<2 mm, 2–15 mm, >15 mm) and by location. Brain hemorrhages were classified as microscopic (<2 mm) and macroscopic.

Results

195/300 (65%) were demented. 194/195 (99%) of the demented had at least one neuropathology. Three independent contributors to dementia were identified: AD‐type tau‐pathology (Braak stage V‐VI), neocortical Lewy‐related pathology, and cortical anterior 2–15 mm infarcts. These were found in 34%, 21%, and 21% of the demented, respectively, with the multivariate odds ratios (OR) for dementia 5.5, 4.5, and 3.4. Factor analysis investigating the relationships between different pathologies identified three separate factors: (1) AD‐spectrum, which included neurofibrillary tau, Aβ plaque, and neocortical Lewy‐related pathologies and CAA (2) >2 mm cortical and subcortical infarcts, and (3) <2 mm cortical microinfarcts and microhemorrhages. Multipathology was common and increased the risk of dementia significantly.

Interpretation

These results indicate that AD‐type neurodegenerative processes play the most prominent role in twilight cognitive decline. The high prevalence of both neurodegenerative and vascular pathologies indicates that multiple preventive and therapeutic approaches are needed to protect the brains of the oldest old.

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.

Plasma homocysteine, Alzheimer and cerebrovascular pathology: a population-based autopsy study

Elevated plasma total homocysteine is associated with increased risk of dementia/Alzheimer's disease, but underlying pathophysiological mechanisms are not fully understood. This study investigated possible links between baseline homocysteine, and post-mortem neuropathological and magnetic resonance imaging findings up to 10 years later in the Vantaa 85+ population including people aged ≥85 years. Two hundred and sixty-five individuals had homocysteine and autopsy data, of which 103 had post-mortem brain magnetic resonance imaging scans. Methenamine silver staining was used for amyloid-β and modified Bielschowsky method for neurofibrillary tangles and neuritic plaques. Macroscopic infarcts were identified from cerebral hemispheres, brainstem and cerebellum slices. Standardized methods were used to determine microscopic infarcts, cerebral amyoloid angiopathy, and α-synuclein pathology. Magnetic resonance imaging was used for visual ratings of the degree of medial temporal lobe atrophy, and periventricular and deep white matter hyperintensities. Elevated baseline homocysteine was associated with increased neurofibrillary tangles count at the time of death: for the highest homocysteine quartile, odds ratio (95% confidence interval) was 2.60 (1.28-5.28). The association was observed particularly in people with dementia, in the presence of cerebral infarcts, and with longer time between the baseline homocysteine assessment and death. Also, elevated homocysteine tended to relate to amyloid-β accumulation, but this was seen only with longer baseline-death interval: odds ratio (95% confidence interval) was 2.52 (0.88-7.19) for the highest homocysteine quartile. On post-mortem magnetic resonance imaging, for the highest homocysteine quartile odds ratio (95% confidence interval) was 3.78 (1.12-12.79) for more severe medial temporal atrophy and 4.69 (1.14-19.33) for more severe periventricular white matter hyperintensities. All associations were independent of several potential confounders, including common vascular risk factors. No relationships between homocysteine and cerebral macro- or microinfarcts, cerebral amyoloid angiopathy or α-synuclein pathology were detected. These results suggest that elevated homocysteine in adults aged ≥85 years may contribute to increased Alzheimer-type pathology, particularly neurofibrillary tangles burden. This effect seems to be more pronounced in the presence of cerebrovascular pathology. Randomized controlled trials are needed to determine the impact of homocysteine-lowering treatments on dementia-related pathology.

Genetic studies in Alzheimer's disease

Alzheimer's disease (AD), the most common cause of dementia in aged populations, is believed to be caused by both environmental factors and genetic variations. Extensive linkage and association studies have established that a broad range of loci are associated with AD, including both causative and susceptibility (risk factor) genes. So far, at least three genes, APP, PS1, and PS2, have been identified as causative genes. Mutations in these genes have been found to cause mainly early-onset AD. On the other hand, APOE has been identified to be the most common high genetic risk factor for late-onset AD. Polymorphisms in the coding region, intron, and promoter region of certain genes constitute another kind of genetic variation associated with AD. A number of other genes or loci have been reported to have linkage with AD, but many show only a weak linkage or the results are not well reproduced. Currently, the measurable genetic associations account for about 50% of the population risk for AD. It is believed that more new loci will be found to associate with AD, either as causative genes or genetic risk factors, and that eventually the understanding of genetic factors in the pathogenesis of AD will be important for our efforts to cure this illness.

Genome-wide data-mining of candidate human splice translational efficiency polymorphisms (STEPs) and an online database

BACKGROUND

Variation in pre-mRNA splicing is common and in some cases caused by genetic variants in intronic splicing motifs. Recent studies into the insulin gene (INS) discovered a polymorphism in a 5' non-coding intron that influences the likelihood of intron retention in the final mRNA, extending the 5' untranslated region and maintaining protein quality. Retention was also associated with increased insulin levels, suggesting that such variants--splice translational efficiency polymorphisms (STEPs)--may relate to disease phenotypes through differential protein expression. We set out to explore the prevalence of STEPs in the human genome and validate this new category of protein quantitative trait loci (pQTL) using publicly available data.

METHODOLOGY/PRINCIPAL FINDINGS

Gene transcript and variant data were collected and mined for candidate STEPs in motif regions. Sequences from transcripts containing potential STEPs were analysed for evidence of splice site recognition and an effect in expressed sequence tags (ESTs). 16 publicly released genome-wide association data sets of common diseases were searched for association to candidate polymorphisms with HapMap frequency data. Our study found 3324 candidate STEPs lying in motif sequences of 5' non-coding introns and further mining revealed 170 with transcript evidence of intron retention. 21 potential STEPs had EST evidence of intron retention or exon extension, as well as population frequency data for comparison.

CONCLUSIONS/SIGNIFICANCE

Results suggest that the insulin STEP was not a unique example and that many STEPs may occur genome-wide with potentially causal effects in complex disease. An online database of STEPs is freely accessible at http://dbstep.genes.org.uk/.

Neurofibrillary tau pathology modulated by genetic variation of alpha-synuclein

We analyzed whether genetic variation of alpha-synuclein modulates the extent of neuropathological changes in a population-based autopsied sample of 272 elderly Finns. None of the 11 markers was associated with the extent of neocortical beta-amyloid pathology. The intron 4 marker rs2572324 was associated with the extent of neurofibrillary pathology (p = 0.0006, permuted p = 0.004; Braak stages IV-VI vs 0-II). The same variant also showed a trend for association with neocortical Lewy-related pathology. These results suggest for the first time that variation of alpha-synuclein modulates neurofibrillary tau pathology and support the recent observations of an interaction of alpha-synuclein and tau in neurodegeneration.

Senile systemic amyloidosis affects 25% of the very aged and associates with genetic variation in alpha2-macroglobulin and tau: a population-based autopsy study

BACKGROUND

Senile systemic amyloidosis (SSA) is characterized by deposition of wild-type transthyretin (TTR)-based amyloid in parenchymal organs in elderly individuals. Previously, no population-based studies have been performed on SSA.

METHODS

Here we have studied the prevalence and risk factors for SSA in a Finnish autopsied population aged 85 or over, as part of the population-based Vantaa 85+ Autopsy Study (n = 256). The diagnosis of SSA was based on histological examination of myocardial samples stained with Congo red and anti-TTR immunohistochemistry. The genotype frequencies of 20 polymorphisms in 9 genes in subjects with and without SSA were compared.

RESULTS

The prevalence of SSA was 25%. SSA was associated with age, myocardial infarctions, the G/G (Val/Val) genotype of the exon 24 polymorphism in the alpha2-macroglobulin (alpha2M), and the H2 haplotype of the tau gene (P-values 0.002, 0.004, 0.042, and 0.016).

CONCLUSION

This population-based study shows that SSA is very common in old individuals, affecting one-quarter of people aged over 85 years. Myocardial infarctions and variation in the genes for alpha2M and tau may be associated with SSA.

Population-based neuropathological studies of dementia: design, methods and areas of investigation--a systematic review

Background

Prospective population-based neuropathological studies have a special place in dementia research which is under emphasised.

Methods

A systematic review of the methods of population-based neuropathological studies of dementia was carried out. These studies were assessed in relation to their representativeness of underlying populations and the clinical, neuropsychological and neuropathological approaches adopted.

Results

Six studies were found to be true population-based neuropathological studies of dementia in the older people: the Hisayama study (Japan); Vantaa 85+ study (Finland); CC75C study (Cambridge, UK); CFAS (multicentre, UK); Cache County study (Utah, USA); HAAS (Hawaï, USA). These differ in the core characteristics of their populations. The studies used standardised neuropathological methods which facilitate analyses on: clinicopathological associations and confirmation of diagnosis, assessing the validity of hierarchical models of neuropathological lesion burden; investigating the associations between neuropathological burden and risk factors including genetic factors. Examples of findings are given although there is too little overlap in the areas investigated amongst these studies to form the basis of a systematic review of the results.

Conclusion

Clinicopathological studies based on true population samples can provide unique insights in dementia. Individually they are limited in power and scope; together they represent a powerful source to translate findings from laboratory to populations.

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.

Association study of the A2M and LRP1 Genes with Alzheimer disease in the Han Chinese

BACKGROUND

Low-density lipoprotein receptor-related protein 1 (LRP1) and alpha-2-macroglobulin (A2M) are two plausible candidate genes for Alzheimer disease (AD) based on their important biological function and positional information. To date, numerous studies have investigated their possible association with AD but the results are controversial.

METHODS

To investigate the potential genetic contribution of the two genes in the Han Chinese population, we performed a case-control association study using 10 polymorphisms (4 in LRP1 and 6 in A2M) that span approximately the whole corresponding gene.

RESULTS

Comparison of allele, genotype, and haplotype frequencies for polymorphisms in A2M revealed no significant differences between patients and control subjects. For the LRP1 gene, however, we found an overrepresentation of the CTCG haplotype in the control group (p = .002). The difference was still of statistical significance in the apolipoprotein E (APOE) epsilon 4 negative subjects (p(CTCG) = .003). Multiple logistic regression analysis did not show any evidence of synergism between A2M, LRP1, and APOE.

CONCLUSIONS

Our results indicate that the CTCG haplotype of LRP1 may reduce the risk of late-onset AD, but A2M is not associated with this disease in the Han Chinese population.

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.

Chromosome 21 BACE2 haplotype associates with Alzheimer's disease: A two-stage study

Genetic linkage studies have provided evidence for a late-onset Alzheimer's disease (AD) susceptibility locus on chromosome 21q. We have tested, in a two-stage association study, whether allelic or haplotype variation of the beta-amyloid cleaving enzyme-2 (BACE2) locus on chromosome 21q affects the risk of late-onset AD. In stage-1, an unselected population-based sample of Finns aged 85 years or over (n=515) was analysed. Neuropathologic examination including beta-amyloid load quantification was possible in over 50% (n=264) of these subjects. AD patients (n=100) and controls (n=48) were defined by modified neuropathological NIA-RI criteria. Positive associations were taken as a hypothesis, and tested in stage-2 using 483 AD families from the USA. Four single nucleotide polymorphisms (SNPs) of BACE2 gene were tested in stage-1. A SNP close to exon-6 was associated with neuropathologically verified AD (p=0.02) and also with beta-amyloid load in non-selected autopsied subjects after conditioning with APOE genotype (p=0.001). In haplotype analysis a specific, relatively common haplotype (H5) was found to associate with AD (p=0.004) and a second haplotype (H7) showed a weaker association with protection against AD (p=0.04). In stage-2, the SNP association was not replicated, whereas the haplotype H5 association was replicated (p=0.004) and a trend to association was found with the putative protective haplotype H7 (two-sided p=0.08). BACE2 haplotype association with AD in two independent datasets provides further evidence for an AD susceptibility locus on chromosome 21q within or close to BACE2.

Cholesterol at the crossroads: Alzheimer's disease and lipid metabolism

Alzheimer's Disease (AD) is a devastating disease that affects millions of elderly persons. Despite years of intense investigations, genetic risk factors that affect the majority of AD cases have yet to be determined. Recent studies suggest that cholesterol metabolism has integral part in AD pathogenesis, suggesting that genes that regulate lipid metabolism may also play roles in AD. This review will first describe emerging evidence that links cholesterol to the mechanisms thought to underlie AD. Based on this rationale, candidate genes located in regions implicated in AD that have roles in lipid metabolism will then be discussed.

Reference distributions for alpha2-macroglobulin: a practical, simple and clinically relevant approach in a large cohort

In this 11th article in a series, reference values of serum levels alpha(2)-macroglobulin alpha(2)M) are examined. The study is based on a cohort of 40,420 Caucasian individuals from northern New England that were tested in our laboratory between 1994 and 2000. Measurements were standardized against Certified Reference Material (CRM 470)/Reference Preparation for Proteins in Human Serum (RPPHS) and the results analyzed using a previously described statistical approach. Individuals with unequivocal laboratory evidence of inflammation (C-reactive protein >10 mg/L) were excluded in one leg of the study and included in the other, confirming that alpha(2)M does not respond to acute phase drive in man. Nephrotic syndrome, diabetes mellitus, and chronic liver disease have significant effect on levels of alpha(2)M. Dramatic changes occur during life with males higher from birth to age 12, females thereafter have higher values until the ninth decade. When values were expressed as multiples of the age- and gender-specific median levels, the resulting distributions fitted a log-Gaussian distribution well over a broad range. When patient data are normalized in this manner, the distribution parameters can be used to assign a centile corresponding to an individual's measurement thus simplifying interpretation.

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.

Candidate gene association studies in sporadic Alzheimer's disease

The genetics of Alzheimer's disease (AD) is complex. Three genes (amyloid precursor protein, presenilin 1 and presenilin 2) have been described in the relatively rare, early-onset, autosomal dominant familial form of AD. In the common, non-familial (sporadic) late-onset AD, the major known genetic risk factor is the epsilon4 allele of the apolipoprotein E (APOE) gene. However, at least half of the people who develop AD do not carry this allele, and not all people who do carry this allele develop AD even if they live to an old age. Therefore, approximately 30 other candidate genes involving a protein in a critical pathway in the pathogenesis of disease (principally interaction with amyloid-beta, oxidative stress and inflammation/apoptosis) have been considered as risk factors for sporadic AD. Then these genes have been sequenced in search of genetic variability or polymorphisms, and each putative polymorphism has been reported to alter the risk of AD either directly or by an interaction with the APOE epsilon4 allele. However, positive-association studies with these candidate genes have not been consistently confirmed.

Laminin affects polymerization, depolymerization and neurotoxicity of Abeta peptide

Amyloid deposition in Alzheimer fibrils forms neurotoxic senile plaques in a process that may be modulated by associated proteins. In this work we demonstrate the ability of laminin-1 and laminin-2 to inhibit fibril formation and toxicity on cultured rat hippocampal neurons. We confirm that the laminin-1-derived peptide YFQRYLI inhibits efficiently both fibril formation and neurotoxicity and show that the IKVAV peptide inhibits amyloid neurotoxicity despite its slight inhibition of fibril formation. On other hand, laminin-1 induces disaggregation of preformed fibrils in vitro, characterized as a progressive disassembly of fibrils into protofibrils and further clearance of these latter species, leading to a continual inhibition of amyloid neurotoxicity.

Lack of association of the two polymorphisms in alpha-2 macroglobulin with Alzheimer disease

Alzheimer disease is a complex neurodegenerative disorder that is characterized by cognitive decline and distinct neuropathology. The gene for alpha-2 macroglobulin (A2M) on chromosome 12 has two polymorphisms that, in some cases, are associated with Alzheimer disease. We examined these two polymorphisms in our families in the DNA Bank (a collection of DNA samples from families with Alzheimer disease in Texas). Using both association studies and sib transmission/disequilibrium tests, we found no association of the two polymorphisms with the disease in our collection. In addition, we did not find an association of the disease with the two polymorphisms in A2M in a small subset of National Institute of Mental Health (NIMH) families. Thus, our studies do not support the A2M polymorphisms as a risk factor for Alzheimer disease.

Distinct binding sites in the structure of alpha 2-macroglobulin mediate the interaction with beta-amyloid peptide and growth factors

Alpha(2)-macroglobulin (alpha(2)M) and its receptor, low density lipoprotein receptor-related protein (LRP), function together to facilitate the cellular uptake and degradation of beta-amyloid peptide (Abeta). In this study, we demonstrate that Abeta binds selectively to alpha(2)M that has been induced to undergo conformational change by reaction with methylamine. Denatured alpha(2)M subunits, which were immobilized on polyvinylidene difluoride membranes, bound Abeta, suggesting that alpha(2)M tertiary and quaternary structure are not necessary. To determine whether a specific sequence in alpha(2)M is responsible for Abeta binding, we prepared and analyzed defined alpha(2)M fragments and glutathione S-transferase-alpha(2)M peptide fusion proteins. A single sequence, centered at amino acids (aa) 1314-1365, was identified as the only major Abeta-binding site. Importantly, Abeta did not bind to the previously characterized growth factor-binding site (aa 718-734). Although the Abeta binding sequence is adjacent to the binding site for LRP, the results of experiments with mutated fusion proteins indicate that the two sites are distinct. Furthermore, a saturating concentration of Abeta did not inhibit LRP-mediated clearance of alpha(2)M-MA in mice. Using various methods, we determined that the K(D) for the interaction of Abeta with its binding site in the individual alpha(2)M subunit is 0.7-2.4 microm. The capacity of alpha(2)M to bind Abeta and deliver it to LRP may be greater than that predicted by the K(D), because each alpha(2)M subunit may bind Abeta and the bound Abeta may multimerize. These studies suggest a model in which alpha(2)M has three protein interaction sites with distinct specificities, mediating the interaction with Abeta, growth factors, and LRP.

ApoE epsilon3-haplotype modulates Alzheimer beta-amyloid deposition in the brain

ApoE epsilon4 allele increases the risk of late-onset Alzheimer disease (AD) as well as the amount of beta-amyloid deposition in the brain. Because half of AD patients do not have ApoE epsilon4, it is important to search for other determinants of ApoE that modify AD risk. We tested whether the haplotype background of the most common ApoE allele, epsilon3, influences brain amyloid deposition or the risk of neuropathologically verified AD in a population-based sample of elderly Finns. To exclude the effects of ApoE protein polymorphism we focused these analyses on subjects homozygous for epsilon3. Haplotypes were defined using polymorphisms at positions - 491 and -219 of the ApoE promoter and at position +113 of intron-1. We found that epsilon3-haplotypes containing the promoter allele -219T were associated with reduced amyloid deposition and reduced risk of neuropathologically verified AD as compared to epsilon3-haplotypes containing -219G. The functional polymorphism(s) responsible for the haplotypic difference remains to be identified. These results indicate that there is significant allelic variation in the ApoE gene region, which modulates brain amyloid deposition and AD risk, independent of the ApoE protein polymorphism.

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.

Association of lipoprotein lipase Ser447Ter polymorphism with brain infarction: a population-based neuropathological study

BACKGROUND

Variants of the lipoprotein lipase (LPL) gene have been shown to influence serum lipid levels, risk of coronary heart disease and, as found recently, risk of clinical ischaemic cerebrovascular disease. Here we tested for an association between brain infarction and two common polymorphisms of the LPL gene, Ser447Ter and Asn291 Ser.

METHOD

To avoid ascertainment and selection bias involved in many association studies, we compared the distribution of these polymorphisms in neuropathologically verified patients (n = 119) vs controls (n = 133) derived from a prospective, population-based study (the Vantaa 85+ study).

RESULTS

The LPL Ter447 variant was negatively associated with neuropathologically verified brain infarcts (P = 0.006), and even more strongly with small brain infarcts (P = 0.004). In addition, we found that the Ter447 variant was associated with higher serum HDL chblesterol (P = 0.004) and lower triglyceride levels (P= 0.003), and that it was negatively associated with pathologically verified severe coronary artery disease (P=0.001) in the Vantaa 85+ study sample. The Asn291Ser polymorphism was not significantly associated with brain infarction.

CONCLUSION

The Ter447 variant of LPL is associated with decreased risk of brain infarction and coronary artery disease in our very elderly population.

Of replications and refutations: the status of Alzheimer's disease genetic research

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder. To date, mutations in three genes (APP, PSEN1, PSEN2) have been described to cause familial early-onset AD. In addition, a common polymorphism in the gene encoding apolipoprotein E (APOE) has been associated with the more common late-onset form of the disease. However, many studies have shown that genetic factors other than APOE play an important role in late-onset AD. Along these lines, a recent report predicted the existence of at least four additional late-onset AD genes, one of which was estimated to have a much greater contribution to age of onset variation than the APOE epsilon 4-allele. However, most of the nearly three dozen loci that have been proposed as putative AD genes to date have been followed by both replications and refutations, making consensus impossible. In this overview, we discuss the current status of genetic research in AD, including a brief summary of applicable analytic tools, and a summary of recent findings suggesting the existence of novel AD genes on chromosomes 10, 11, and 12.

Analysis of alpha-2-macroglobulin-2 allele as a risk factor in Alzheimer's disease

A correlation between a 5-nucleotide deletion polymorphism in the A2M gene and an enhanced risk of developing Alzheimer's disease (AD) was reported. We studied this polymorphism in sporadic AD patients and patients with frontotemporal dementia (FTD) by using an electrophoretical separation of PCR products on a Metaphor gel. Our results did not show any significant difference between A2M-2 allelic frequency (p = 0.89) or genotype frequency (p = 0.97) in the two different clinical series and in control subjects. The frequencies were not significantly different after stratification by APOE epsilon4 status.

Common polymorphisms in LRP and A2M do not affect genetic risk for Alzheimer disease in Northern Ireland

Genetic variation in one of the major APOE receptors in the brain has been associated with increased risk for Alzheimer disease (AD). A C/T polymorphism in exon 3 and a tetranucleotide repeat polymorphism in the 5' region of the low-density lipoprotein receptor-related protein gene have been reported to increase risk in some studies but these reports have not been universally replicated. In addition, genetic variation in another ligand of LRP, alpha-2 macroglobulin (A2M), has also been associated with increased AD risk. However, these reports also remain controversial. We have genotyped both LRP polymorphisms and two polymorphisms in the A2M gene in a large group of clinically well-defined AD cases and controls from the relatively genetically homogeneous Northern Ireland population. Comparison of genotype and allele frequencies for polymorphisms in LRP revealed no significant differences between cases and controls. Multiple logistic regression analysis performed to assess any possible interaction between LRP and APOE revealed little evidence for genetic interaction despite the obvious biological interaction. Genotype and allele comparisons between the groups for the A2M polymorphisms also gave no evidence that either polymorphism increased risk for disease. The results from this study indicate that polymorphisms in LRP and A2M are not associated with increased risk for AD in Northern Ireland.

Alzheimer's disease: genes, proteins, and therapy

Rapid progress in deciphering the biological mechanism of Alzheimer's disease (AD) has arisen from the application of molecular and cell biology to this complex disorder of the limbic and association cortices. In turn, new insights into fundamental aspects of protein biology have resulted from research on the disease. This beneficial interplay between basic and applied cell biology is well illustrated by advances in understanding the genotype-to-phenotype relationships of familial Alzheimer's disease. All four genes definitively linked to inherited forms of the disease to date have been shown to increase the production and/or deposition of amyloid beta-protein in the brain. In particular, evidence that the presenilin proteins, mutations in which cause the most aggressive form of inherited AD, lead to altered intramembranous cleavage of the beta-amyloid precursor protein by the protease called gamma-secretase has spurred progress toward novel therapeutics. The finding that presenilin itself may be the long-sought gamma-secretase, coupled with the recent identification of beta-secretase, has provided discrete biochemical targets for drug screening and development. Alternate and novel strategies for inhibiting the early mechanism of the disease are also emerging. The progress reviewed here, coupled with better ability to diagnose the disease early, bode well for the successful development of therapeutic and preventative drugs for this major public health problem.

Delirium in the non-demented oldest old in the general population: risk factors and prognosis

BACKGROUND

The oldest old are prone to develop delirium. Studies into risk factors for delirium have been carried out predominantly in younger age groups. The aim of this population-based follow-up study was to investigate the risk factors for delirium requiring medical attention and subsequent prognosis in the non-demented general population aged > or = 85 years.

METHOD

The study included the non-demented subjects in the population-based Vantaa 85+ study. After the 3-year observation period, 199 subjects (91% of those surviving) were re-examined and their medical records were evaluated for episodes of delirium. The subjects were followed up with respect to mortality for another 2 years.

RESULTS

During the 3-year observational period, 20 subjects (10%) had been diagnosed as having had an episode of delirium. A Mini-Mental State Examination score of < 24 (odds ratio (OR) 3.44, confidence interval (CI = 95%) 1.27-9.32) and high systolic blood pressure (OR 3.08, CI 1.08-8.79) were identified as independent risk factors for delirium. The association between the delirium episode and a new diagnosis of dementia was significant ( p = 0.001). The mortality rate was greater among those subjects who experienced delirium than among subjects without this syndrome ( p = 0.008).

CONCLUSIONS

Mild cognitive impairment and high systolic blood pressure were found to be risk factors for delirium requiring medical attention in the general non-demented population aged > or = 85 years. The study also highlights the significant association between delirium and a new dementia diagnosis in this age group.

Alpha2-macroglobulin polymorphisms in Italian sporadic and familial Alzheimer's disease

A 5-bp deletion and a Val1000 polymorphism at the alpha(2)-macroglobulin (A2M) gene have recently been reported to be associated with late onset Alzheimer's disease (AD). As recently it has been suggested that the effect of the A2M gene on AD susceptibility may be limited to certain populations or families, we analyzed the segregation of A2M and apolipoprotein E polymorphisms in Italian sporadic and familial AD. We analyzed the two polymorphisms in a total of 346 subjects including 98 controls by polymerase chain reaction-restriction fragment length polymorphism method. Our data do not confirm these associations, in particular we found a significant decrease of the deletion allele in AD with respect to controls. Our data do not support a role for the A2M gene as genetic risk factor for AD.

Association of alpha-2-macroglobulin deletion polymorphism with sporadic Alzheimer's disease in Koreans

Alpha-2-macroglobulin (A2M) deletion polymorphism was recently reported to be associated with Alzheimer's disease (AD) in a way comparable to apolipoprotein E (APOE) polymorphism in a family-based study. However, the association of A2M deletion polymorphism with AD has not been consistently replicated in successive case-controlled studies. In order to evaluate whether this A2M polymorphism is associated with AD in Koreans, we examined the frequencies of the A2M deletion (D) allele and D-bearing genotypes in a group of Koreans composed of 100 sporadic AD patients and 203 control subjects. The frequency of the deletion (D) allele (P=0.046) was significantly different between the total group of AD patients and the controls, although the frequency of the D-bearing genotypes did not attain significance (P=0.078). When the subjects were stratified according to age at onset, there was significant difference in the frequencies of the D allele (P=0.044) and D-bearing genotypes (P=0.041) between late-onset AD patients (> or =65 years) and the controls. However, no significant difference was observed between early-onset AD patients (<65 years) and the control group. Additionally, when we divided the late-onset AD and control subjects by APOE epsilon4 status, the difference of the A2M D allelic frequency was significant only in the APOE epsilon4 negative subjects (P=0.015). In conclusion, our data suggests that the A2M D allele is a modest risk factor for late-onset sporadic AD in Koreans, and the AD risk conferred by the A2M D allele increases in APOE epsilon4 negative subjects.