Association of apolipoprotein E genotype and intronic polymorphism of the presenilin-1 gene with Alzheimer's disease in elderly Taiwan Chinese

Mutations in SORL1 and MTHFDL1 possibly contribute to the development of Alzheimer's disease in a multigenerational Colombian Family

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, affecting over 50 million people worldwide in 2020 and this number will triple to 152 million by 2050. Much of the increase will be in developing countries like Colombia. In familial forms, highly penetrant mutations have been identified in three genes, APP, PSEN1, and PSEN2, supporting a role for amyloid-β peptide. In sporadic forms, more than 30 risk genes involved in the lipid metabolism, the immune system, and synaptic functioning mechanisms. We used whole-exome sequencing (WES) to evaluate a family of 97 members, spanning three generations, with a familiar AD, and without mutations in APP, PSEN1, or PSEN2. We sequenced two affected and one unaffected member with the aim of identifying genetic variants that could explain the presence of the disease in the family and the candidate variants were validated in eleven members. We also built a structural model to try to determine the effect on protein function. WES analysis identified two rare variants in SORL1 and MTHFD1L genes segregating in the family with other potential risk variants in APOE, ABCA7, and CHAT, suggesting an oligogenic inheritance. Additionally, the structural 3D models of SORL1 and MTHFD1L variants shows that these variants produce polarity changes that favor hydrophobic interactions, resulting in local structural changes that could affect the protein function and may contribute to the development of the disease in this family.

Apolipoprotein E Gene Revisited: Contribution of Rare Variants to Alzheimer's Disease Susceptibility in Southern Chinese

BACKGROUND

APOE ε4 is the best-known risk factor for late-onset alzheimer's disease (AD). Population studies have demonstrated a relatively low prevalence of APOE ε4 among Chinese population, implying additional risk factors that are Chinese-specific may exist. Apart from - alleles, genetic variation profile along the full-length APOE has rarely been investigated.

OBJECTIVE

In this study, we filled this gap by comprehensively determining all genetic variations in APOE and investigated their potential associations with late-onset AD and mild cognitive impairment (MCI) in southern Chinese.

METHODS

Two hundred and fifty-seven southern Chinese participants were recruited, of whom 69 were AD patients, 83 had MCI, and 105 were normal controls. Full-length APOE from promoter to 3'UTR regions were sequenced. Genetic variants were identified and compared among the three groups.

RESULTS

While APOE ε4 was more significantly found in AD patients, the prevalence of APOE ε4 in southern Chinese AD patients was the lowest when compared to other areas of China and nearby regions, as well as other countries worldwide. We further identified 13 rare non-singleton variants in APOE. Significantly more AD patients carried any of the rare non-singleton variants than MCI and normal subjects. Such difference was observed in the non-carriers of ε4-allele only. Among the identified rare variants, the potential functional impact was predicted for rs532314089, rs553874843, rs533904656 and rs370594287.

CONCLUSION

Our study suggests an ethnic difference in genetic risk composition of AD in southern Chinese. Rare variants on APOE are a potential candidate for AD risk stratification biomarker in addition to APOE-ε4.

Accumulation of amyloid in cognitive impairment after mild traumatic brain injury

Recent epidemiology studies have indicated that traumatic brain injury (TBI) can increase the risk of developing neurodegenerative diseases such as Alzheimer's disease (AD). Amyloid-β (Aβ) plaques and neurofibrillary tangles are pathological indicators of AD. The accumulation of Aβ is considered the first step of AD pathophysiology. Compelling studies have supported the hypothesis that TBI accelerates the formation and accumulation of Aβ. These findings could link TBI with AD, although the research that reported these findings had limitations, particularly regarding mild TBI (mTBI) patients. The effects of mTBI on Aβ accumulation remain uncertain because of a lack of mTBI pathology data. Using amyloid-positron emission tomography (amyloid-PET), researchers can help to determine whether mTBI increases the accumulation of Aβ, which might be involved in the pathophysiological mechanisms of mTBI in AD, and could be a target for the treatment of neurodegenerative diseases associated with TBI. In this study, we recruited 27 mTBI patients with mTBI in mean 6years before this study (21 mTBI patients without cognitive impairment, 6 mTBI patients with cognitive impairment,) and 10 controls. All of them underwent mini-mental state examination, apolipoprotein E (APOE) genotyping, and amyloid-PET. The results show an increase of amyloid accumulation and allele frequency of APOE4 in the mTBI patients with cognitive impairment. These findings indicate that amyloid accumulation is an important indicator of cognitive impairment, and amyloid-PET should be a safe and useful tool for diagnosing amyloid-related cognitive impairment. APOE allele might play a role in the occurrence of cognitive impairment after mTBI. The contribution of mTBI to the amyloid accumulation requires further study, and mTBI patients should be recruited for longitudinal research with repeated amyloid-PET studies.

Association study and meta-analysis of Alzheimer's disease risk and presenilin-1 intronic polymorphism

Numerous studies have tested for associations between an intronic polymorphism (rs165932) of presenilin-1 (PS-1) gene and the risk of Alzheimer's disease (AD), but results have been conflicting. To throw light on this issue, we investigate the possible involvement of PS-1 genotype in a case-control study based on a relatively stable population in Spain and a meta-analysis of published studies. An examination was conducted of 85 patients with probable or possible AD, along with controls from the same community, by using an chi(2) test for homogeneity and a binary logistic regression model. For comparison purposes, a meta-analysis of data from all available published studies was assessed. In our patients, homozygosity of the allele 2 in the PS-1 gene increased for late-onset AD (OR 2.38, 95% CI 1.07-5.29, P<0.05). The presence of at least one allele of apoE was also associated with AD (OR 4.01, 95% CI 1.93-8.34, p<0.05). The regression model showed that, overall, the presence of the apoE epsilon 4 allele and the PS-1 2/2 genotype were independent factors for the development of AD in our sample. In our genotype-based meta-analysis, the PS-1 2/2 genotype was probably related with AD for the European sub-group (fixed effects model, OR 1.19, 95% CI 1.02-1.37, p<0.05), but there are many confusing factors between different studies. Presenilin-1 2/2 genotype is a risk factor for late onset Alzheimer disease in the Spanish population, and probably, for Europeans.

Proteomic identification of lower apolipoprotein A-I in Alzheimer's disease

Many researches have been trying to find the potential biomarkers for Alzheimer's disease (AD). We hereby used the proteomics method to search for protein expression differences in the serum between AD patients and controls. We enrolled 59 AD patients and 74 age- and sex-matched controls in this study. Ten AD patients and 10 controls were selected for proteomic analysis. Apolipoprotein A-I (ApoA-I) was found to have a lower expression in the AD group by a proteomics two-dimensional gel electrophoresis study. We further measured the serum ApoA-I level which was significantly lower in the AD patients (112.29 +/- 21.33 mg/dl) in comparison to the controls (144.53 +/- 19.91 mg/dl; p < 0.0002). Lower serum ApoA-I levels might be a potential biomarker for AD.

The allele interaction between apolipoprotein epsilon2 and epsilon4 in Taiwanese Alzheimer's disease patients

OBJECTIVE

This study aimed to determine the impact of the present of apolipoprotein epsilon (Apoepsilon) 2 on the relationship between Apoepsilon4 and Alzheimer's disease (AD).

METHOD

We examined ApoE genotypes in 428 Taiwanese patients with AD and 807 controls; all participants were older than 65 years.

RESULTS

The allele frequency of Apoepsilon4 was greater in AD patients than controls, but significantly lower than in Caucasians. The presence of an epsilon2 allele alone was not associated with lower risk for AD, but the presence of an epsilon2 allele was associated with an epsilon4 allele frequency similar to that of controls.

CONCLUSION

The low allele frequency of epsilon4 in persons with an epsilon2 allele suggests that this may be part of the protective effect of epsilon2 against AD.

Lack of association between interleukin-1alpha polymorphism and Alzheimer disease or vascular dementia

Recently, a C/T polymorphism in the promoter region of the interleukin 1-alpha (IL-1alpha) gene (position -889) was reported to be associated with Alzheimer disease. In this study, the polymorphism of IL-1alpha was examined in patients with Alzheimer disease, vascular dementia, and nondemented controls in a Chinese population in Taiwan. No difference was found in the IL-1alpha T allele frequency among the three groups. The predominant polymorphic allele ( approximately 90%) of IL-1alpha was the C allele. The APOE4 allele was overrepresented in the AD cohort. The presence of the APOE4 allele did not influence the IL-1alpha genotype or allele distribution. The prevalence of the IL-1alpha T allele, in particular the homozygous form, was lower than in whites and may account for the lack of association between IL-1alpha C/T polymorphism and Alzheimer disease among Chinese in Taiwan. The presence of the heterozygous IL-1alpha T allele cannot be used for distinguishing Alzheimer disease or vascular dementia from controls.

Coenzyme Q10, antioxidant status and ApoE isoforms

The aim of this study was to inquire the antioxidant status in plasma and lipoproteins isolated from normal subjects possessing different ApoE genotypes. For this purpose we investigated blood samples from 106 healthy blood donors: the distribution of ApoE alleles (E2/E2 = 0.9%, E2/E3 = 10.4%, E2/E4 = 2.8%, E3/E3 = 71.7%, E3/E4 = 12.3% and E4/E4 1.9% with 1, 11, 3, 76, 13, and 2 subjects respectively for each genotype) was in agreement with previous data. Almost no differences were found in the concentrations of both coenzyme Q10 (CoQ10) and vitamin E for the different genotypes. Concentration of CoQ10 in isolated lipoproteins was also similar, in the different genotypes, when referred to cholesterol; CoQ10 in LDL was higher for the E3/E3 subjects when referred to protein. Neither CoQ10 nor vitamin E correlated with paraoxonase (PON) activity or cholesteryl-ester hydroperoxides (CHP). Furthermore, there was no correlation between the same lipophilic antioxidants and CHP levels. The only E2 homozygous subject found had high levels of PON and low levels of CHP; the two E4/E4 subjects had low PON activity together with low levels of CHP.

Genetic risk factors of sporadic Alzheimer's disease among Chinese in Taiwan

To evaluate the genetic factors for AD among a Chinese population in Taiwan, we studied the polymorphisms of six candidate genes of Alzheimer's disease (AD), including the regulatory region of apolipoprotein E (Apo-E, G-186T), the promoter of apolipoprotein E (Apo-E, A-491T), the bleomycin hydrolase gene (BH, A1450G), a mutation of alpha(2)-macroglobulin gene (A2M G2998A), low-density lipoprotein receptor-related protein gene (LRP, C766T), and alpha(1)-antichymotrypsin gene (ACT, -15Ala/Thr) in AD patients and non-affected elder individuals among Taiwanese Chinese. Eighty-two AD patients and 110 non-affected individuals were recruited for this study. We used polymerase chain reaction (PCR) and restriction enzyme digestion to identify their genotypes. The statistical examination was performed by combining the results of our previous reports - apolipoprotein E epsilon4 (ApoE-4), presenilin-1 intronic polymorphism (PS-1, allele 1/2), and the five-nucleotide deletion of alpha(2)-macroglobulin gene (A2M). Among these nine candidate genes of AD, the ApoE-4 allele is the only independent genetic risk factor for AD. The other candidate genes in this study were not associated with the occurrence of AD. In addition, there are no gene-gene interactions.

No association between an intronic polymorphism in the presenilin-1 gene and Alzheimer disease in a German population

A polymorphism in intron 8 of the presenilin-1 (PS-1) gene has been demonstrated to increase the risk for developing late-onset Alzheimer disease (AD). Conflicting results exist for the association between this intronic polymorphism and AD probably due to variations in the PS-1 gene among different ethnic groups. We investigated the genetic association between this intronic polymorphism in the PS-1 gene and AD in a homogenous group of German Caucasians. The control group consisted of healthy subjects and depressed patients. There were no significant differences in the distribution of the PS-1 genotypes and allele frequencies between AD patients and controls. Our data do not support an association between the intronic polymorphism of the PS-1 gene and AD and there was no interaction between the PS-1 genotype and apolipoprotein E epsilon4 allele.

Lack of association of presenilin-1 intron-8 polymorphism with neuropathological features of Alzheimer's disease

Over 45 mutations within the coding region of presenilin-1 (PS-1) are associated with an autosomal dominant form of Alzheimer's disease. Recently allele 1 of a polymorphism within intron-8 was reported to be in disequilibrium with Alzheimer's disease in a group of patients with sporadic Alzheimer's disease. This association has been replicated in some, but not all, studies. To determine whether the PS-1 intronic polymorphism is overrepresented in Alzheimer's disease in an autopsy-proven series, and to examine whether allele 1 is associated with a specific neuropathological phenotype, polymerase chain reaction based technique was used to assess the genotype in 85 cases of Alzheimer's disease. The resulting genotypes were compared with age of onset, duration of illness, and quantitative neuropathological measures of Abeta(total), Abeta(1-40), Abeta(1-42), neurofibrillary tangle number and neuron number. The 1/1 genotype did not associate with any differences in the clinical or neuropathological phenotype. These data suggest that the PS-1 intron-8 polymorphism does not strongly impact the clinical or neuropathologic features of Alzheimer's disease.