TOMM40 intron 6 poly-T length,age at onset,and neuropathology of AD in individuals with APOE ɛ3/ɛ3

BackgroundThis study investigates the association between TOMM40 poly-T length, age at onset, and neuropathology in individuals with Alzheimer’s disease (AD) with the apolipoprotein E (APOE) ɛ3/ɛ3 allele.MethodsThirty-two presenilin 1 (PSEN1) mutation carriers with AD, 27 presenilin 2 (PSEN2) mutation carriers with AD, 59 participants with late-onset AD (LOAD), and 168 autopsied subjects from a community-based cohort were genotyped for TOMM40 intron 6 poly-T (rs10524523) length using short tandem repeat assays.ResultsAmong AD individuals with PSEN2 mutations, the presence of a long poly-T was associated with an earlier age at onset, whereas there were no such associations for subjects with PSEN1 mutations or LOAD. In community-based participants, the presence of a long poly-T was associated with increased neuritic tangles and a greater likelihood of pathologically diagnosed AD.ConclusionTOMM40 intron 6 poly-T length may explain some of the variation in age at onset in PSEN2 familial AD and may be associated with AD neuropathology in persons with APOE ɛ3/ɛ3.     

Biochemical Studies of Poly-T Variants in the Alzheimer's Disease Associated TOMM40 Gene

The apolipoprotein E (APOE) gene remains the most strongly established risk factor for late onset Alzheimer's disease (LOAD). Recently the gene, TOMM40, which is in linkage disequilibrium with APOE, was identified to be associated with LOAD in genome-wide association studies. One of the identified polymorphisms in TOMM40 is rs10524523, which is located in intron 6 and composed of thymidine repeats varying between 14 to 36 base-pairs in length. Reported results are contradictory in regard to the very long poly-T variant that has been associated with both increased and decreased risk of LOAD. Our study aimed to elucidate the functional implication of rs10524523 in an in vitro model of human fibroblast cells obtained from cognitively healthy APOE ε3/ε4 carriers harboring very long or short poly-T variants coupled to their APOE ε3 allele. We have studied (i) expression levels of TOM40 protein and mRNA, (ii) TOM40 mRNA splicing, and (iii) mitochondrial function and morphology; and we have found no significant differences in regards to very long or short poly-T variant.     

TOMM40 rs10524523 polymorphism's role in late-onset Alzheimer's disease and in longevity

Recently, it has been reported that TOMM40 variable-length poly-T sequence polymorphism (rs10524523) in combination with APOE alleles (E2, E3, E4) significantly influences late-onset Alzheimer's disease (LOAD) age of onset. In a group of 414 LOAD patients, 173 centenarians and 305 neurologically healthy individuals, we investigated the impact of TOMM40 poly-T tracts on LOAD incidence, age of onset, and longevity. TOMM40 allelic variants were classified into four categories: short (S; 14-16T), long a (La; 20-22T), long b (Lb; 26-30T), and very long (VL; 31-39T). Our results demonstrate that La and Lb share similar characteristics in affecting LOAD risk, thus for some analyses they were combined into L category. We observed significantly lower frequency of VL allele (p < 0.0001) and significantly higher frequency of L alleles in the LOAD patients compared to the control individuals (p < 0.0001). S/S, S/VL, and VL/VL genotypes and VL-E2, S-E3, VL-E3 haplotypes are significantly associated with lower LOAD risk. VL-E3 haplotype carriers significantly more frequently developed LOAD when they were ≥79 years old. Additionally, S/L genotype is associated with a significantly increased LOAD risk (p < 0.0001). We conclude that in the carriers of TOMM40-APOE haplotypes comprising E4 allele, the TOMM40 rs10524523 allele does not play substantial role in establishing LOAD risk. Nevertheless, TOMM40 L allele increases the risk when E4 is absent. Finally, L allele, as well as genotypes (S/L, V/L) and haplotypes (L-E3, L-E4) comprising L significantly reduce the likelihood of living up to 100 years.     

The effects of the TOMM40 poly-T alleles on Alzheimer's disease phenotypes

The TOMM40 poly-T is a polymorphism in intron 6 of the TOMM40 gene, which is adjacent to and in linkage disequilibrium with APOE. Roses et al. identified the association between the length of TOMM40 poly-T with the risk and age of onset of late-onset Alzheimer's disease (LOAD). Following the original discovery, additional studies found associations between the TOMM40 poly-T and LOAD-related phenotypes independent of APOE genotypes, while others did not replicate these associations. Furthermore, the identity of the TOMM40 poly-T risk allele has been controversial between different LOAD-related phenotypes. Here, we propose a framework to address the conflicting findings with respect to the TOMM40 poly-T allele associations with LOAD phenotypes and their functional effects. The framework is used to interpret previous studies as means to gain insights regarding the nature of the risk allele, very long versus short. We suggest that the identity of the TOMM40 poly-T risk allele depends on the phenotype being evaluated, the ages of the study subjects at the time of assessment, and the context of the APOE genotypes. In concluding remarks, we outline future studies that will inform the mechanistic interpretation of the genetic data.     

Functional relevance of mitochondrial abnormalities in sporadic inclusion body myositis

Cytochrome c oxidase (COX)-deficient fibers and multiple mitochondrial DNA (mtDNA) deletions are frequent findings in sporadic inclusion body myositis (s-IBM). However, the functional impact of these defects is not known. We investigated oxygen desaturation during exercise using the forearm exercise test, accumulation of lactate during exercise using a cycle ergometry test and mitochondrial changes (COX-deficient fibers, biochemical activities of respiratory chain complexes, multiple mtDNA deletions by long-range polymerase chain reaction) in 10 patients with s-IBM and compared the findings with age and sex-matched normal and diseased controls (without mitochondrial disorders) as well as patients with mitochondrial disorder due to nuclear gene defects resulting in multiple mtDNA deletions (MITO group). The mean age of the s-IBM patients was 68.2 ± 5.7 years (range: 56–75). Patients with s-IBM had statistically significantly reduced oxygen desaturation (ΔsO₂) during the handgrip exercise (p < 0.05) and elevated peak serum lactate levels during cycle ergometry compared to normal controls (p < 0.05). The percentage of COX-deficient fibers in s-IBM and MITO patients was significantly increased compared to normal controls (p < 0.01). Five out of nine s-IBM patients had multiple mtDNA deletions. Thirty-three percent of s-IBM patients showed an increased citrate synthase content and decreased activities of complex IV (COX). The biochemical pattern of respiratory chain complexes in patients with s-IBM and MITO was similar. Histopathological analysis showed similar changes in s-IBM and MITO due to nuclear gene defects. Functional tests reflecting mitochondrial impairment suggest a contribution of mitochondrial defects to disease-related symptoms such as fatigue and exertion-induced symptoms.     

TOMM40 and APOE: Requirements for replication studies of association with age of disease onset and enrichment of a clinical trial

A number of recent studies have not replicated the association of the translocase of the outer mitochondrial membrane pore subunit (TOMM40) rs10524523 polymorphism, which is in linkage disequilibrium with apolipoprotein E (APOE), with age of onset of Alzheimer's disease (AD). This perspective describes the differences between these later studies and the original experiments. We highlight the necessity for using standardized and informative assessment tools and processes when determining the age of development of AD or AD symptoms, and also stress that this clinical phenotype is best measured reliably in prospective studies during which subjects are monitored over time. This is true when assessing potential biomarkers for age of onset and when assessing the therapeutic potential of medicines that may delay the onset or progression of this disease.     

Intraneuronal amyloid β accumulation and oxidative damage to nucleic acids in Alzheimer disease

In an analysis of amyloid pathology in Alzheimer disease, we used an in situ approach to identify amyloid-β (Aβ) accumulation and oxidative damage to nucleic acids in postmortem brain tissue of the hippocampal formation from subjects with Alzheimer disease. When carboxyl-terminal-specific antibodies directed against Aβ40 and Aβ42 were used for immunocytochemical analyses, Aβ42 was especially apparent within the neuronal cytoplasm, at sites not detected by the antibody specific to Aβ-oligomer. In comparison to the Aβ42-positive neurons, neurons bearing oxidative damage to nucleic acids were more widely distributed in the hippocampus. Comparative density measurements of the immunoreactivity revealed that levels of intraneuronal Aβ42 were inversely correlated with levels of intraneuronal 8-hydroxyguanosine, an oxidized nucleoside (r = ? 0.61, p < 0.02). Together with recent evidence that the Aβ peptide can act as an antioxidant, these results suggest that intraneuronal accumulation of non-oligomeric Aβ may be a compensatory response in neurons to oxidative stress in Alzheimer disease.     

Family history and TOMM40 ‘523 interactive associations with memory in middle-aged and Alzheimer's disease cohorts

Introduction

Family history (FH) of Alzheimer's disease (AD) affects mitochondrial function and may modulate effects of translocase of the outer mitochondrial membrane 40 kDa (TOMM40) rs10524523 (‘523) poly-T length on memory decline.

Changes in brain amyloid-β accumulation after donepezil administration

Recent studies using the mouse model of Alzheimer’s disease (AD) have shown that donepezil administration reduces brain amyloid-β (Aβ) accumulation. This study investigated whether donepezil administration can reduce brain Aβ accumulation in human patients with AD. Ten patients with AD underwent two ¹¹C-Pittsburgh Compound B positron emission tomography sessions approximately one year apart to measure brain Aβ accumulation before and after donepezil treatment. Volumes-of-interest were placed on Aβ-preferred regions, and the standardized uptake value ratio (SUVR) was calculated considering the cerebellum as a reference region. Three and seven patients received 10 mg and 5 mg of donepezil, respectively. SUVR was significantly higher in the second than in the first session (P = 0.026). This study showed that one year of donepezil administration does not reduce brain Aβ accumulation in human patients with AD.     

EEG functional connectivity and ApoE genotype in Alzheimer’s disease and controls

ObjectiveWe examined the relation between Apolipoprotein E ε4 allele (ApoE ε4) genotype and functional connectivity measured by Electroencephalography (EEG) in patients with Alzheimer’s disease (AD) and patients with subjective complaints (SC).MethodsWe included 43 patients with AD (age (SD) = 74.2 (4.0), m/f = 22/21; 30 of ApoE ε4 carriers) and 21 patients with SC (age (SD) = 73.2 (5.2), m/f = 13/8; 7 ApoE ε4 carriers) for this study. Resting state EEGs were recorded in all subjects. Synchronisation likelihood (SL) between local cortical areas was compared in the alpha and beta band according to ApoE ε4 status and diagnosis.ResultsApoE ε4 carriers had higher SL values in lower and upper alpha band, in both diagnostic groups. In upper alpha band and beta band AD patients had lower SL than patients with SC, was irrespective of ApoE status.ConclusionThe effects of AD and ApoE ε4 on functional connectivity are opposite and independent.SignificanceThe observed increase in SL in both AD and patients with SC carrying ApoE ε4 suggests a strong genetic impact of ApoE ε4 on brain function.     

Longitudinal modeling of cognitive aging and the TOMM40 effect

BackgroundTOMM40 (translocase of the outer mitochondrial membrane pore subunit) is in linkage disequilibrium with apolipoprotein E (APOE). APOE e4 is linked to long (L; 21–29 T residues) poly-T variants within intron 6 of TOMM40, whereas APOE e3 can be associated with either a short (S; <21 T residues) or very long (VL; >29 T residues) variant. To assess the possible contribution of TOMM40 to Alzheimer’s disease onset, we compared the effects of TOMM40 and APOE genotype on preclinical longitudinal memory decline.MethodsAn APOE e4–enriched cohort of 639 cognitively normal individuals aged 21 to 97 years with known TOMM40 genotype underwent longitudinal neuropsychological testing every 2 years. We estimated the longitudinal effect of age on memory using statistical models that simultaneously modeled cross-sectional and longitudinal effects of age on the Auditory Verbal Learning Test Long-Term Memory score by APOE, TOMM40, and the interaction between the two.ResultsThere were significant effects overall for both TOMM40 (linear effect, P = .04; quadratic effect, P = .03) and APOE (linear effect, P = .06; quadratic effect, P = .008), with no significant interaction (P = .63). In a piecewise model, there was a significant TOMM40 effect before age 60 years (P = .009), characterized by flattened test–retest improvement (VL/VL subgroup only) but no significant APOE effect, and a significant APOE effect after age 60 years (P = .006), characterized by accelerated memory decline (e4 carriers) but no significant TOMM40 effect.ConclusionBoth TOMM40 and APOE significantly influence age-related memory performance, but they appear to do so independently of each other.     

A homopolymer polymorphism in the TOMM40 gene contributes to cognitive performance in aging

IntroductionA highly polymorphic T homopolymer was recently found to be associated with late-onset Alzheimer’s disease risk and age of onset.ObjectiveTo explore the effects of the polymorphic polyT tract (rs10524523, referred as ‘523’) on cognitive performance in cognitively healthy elderly individuals.MethodsOne hundred eighty-one participants were recruited from local independent-living retirement communities. Informed consent was obtained, and participants completed demographic questionnaires, a conventional paper-and-pencil neuropsychological battery, and the computerized Cambridge Neuropsychological Test Automated Battery (CANTAB). Saliva samples were collected for determination of the TOMM40 ‘523’ (S, L, VL) and the apolipoprotein E (APOE) (ɛ2, 3, 4) genotypes. From the initial sample of 181 individuals, 127 were eligible for the association analysis. Participants were divided into three groups based on ‘523’ genotypes (S/S, S/L-S/VL, and L/L-L/VL-VL/VL). Generalized linear models were used to evaluate the association between the ‘523’ genotypes and neuropsychological test performance. Analyses were adjusted for age, sex, education, depression, and APOE ɛ4 status. A planned subanalysis was undertaken to evaluate the association between ‘523’ genotypes and test performance in a sample restricted to APOE ɛ3 homozygotes.ResultsThe S homozygotes performed better, although not significantly, than the S/L-S/VL and the VL/L-L/VL-VL/VL genotype groups on measures associated with memory (CANTAB Paired Associates Learning, Verbal Recognition Memory free recall) and executive function (CANTAB measures of Intra-Extra Dimensional Set Shift). Follow-up analysis of APOE ɛ3 homozygotes only showed that the S/S group performed significantly better than the S/VL group on measures of episodic memory (CANTAB Paired Associates Learning and Verbal Recognition Memory free recall), attention (CANTAB Rapid Visual Information Processing latency), and executive function (Digit Symbol Substitution). The S/S group performed marginally better than the VL/VL group on Intra-Extra Dimensional Set Shift. None of the associations remained significant after applying a Bonferroni correction for multiple testing.ConclusionsResults suggest important APOE-independent associations between the TOMM40 ‘523’ polymorphism and specific cognitive domains of memory and executive control that are preferentially affected in early-stage Alzheimer’s disease.     

SIRT2 polymorphism rs10410544 is associated with Alzheimer's disease in a Han Chinese population

Sirtuin 2 (SIRT2) is a strong protein deacetylase, which is highly expressed in central nervous system. Recently, an association between SIRT2 rs10410544 polymorphism and late-onset Alzheimer's disease (LOAD) was found in the APOEε4-negative Caucasian population. To investigate the potential association between the rs10410544 C/T polymorphism of SIRT2 and the risk of LOAD, we conducted an independent replication case–control study in a Northern Han Chinese population comprising 1133 cases and 1159 healthy controls being matched for age and gender. The results revealed that there were significant differences in genotype and allele frequencies between LOAD cases and controls (genotype P = 0.008, allele P = 0.009). When compared with the C allele, the T allele of rs10410544 demonstrated a 1.709-fold risk for developing LOAD. After stratification by apolipoprotein E (APOE) ε4-carrying status, only APOEε4 noncarriers (P = 0.035, adjusted OR = 1.656, 95% CI: 1.036–2.647) showed the relation between LOAD and SIRT2 rs10410544 T allele. This study provides the evidence that the rs10410544 C/T polymorphism of SIRT2 was associated with genetic susceptibility to LOAD in a Northern Han Chinese population.     

Association of polymorphisms in the LRP1 and A2M genes with Alzheimer’s disease in the Northern Chinese Han population

Low-density lipoprotein receptor-related protein1 (LRP1) and alpha-2-macroglobulin (A2M) are candidate genes for sporadic Alzheimer’s disease (SAD). It is not clear whether the LRP1 exon 3 and A2M exon 24 polymorphisms are associated with SAD. In the present study, we used direct sequencing to genotype the LRP1 C766T (rs1799986) polymorphism in exon 3 and the A2M I1000V (rs669) polymorphism in exon 24 in 364 patients with SAD and 291 healthy control subjects from the Northern Chinese Han population. The distributions of LRP1 genotypes (chi-squared [χ²] = 7.25, degrees of freedom [d.f.] = 2, p = 0.027) and alleles (χ² = 8.154, d.f. = 1, p = 0.004) were significantly different between patients and controls who were apolipoprotein E (APOE) ε4 positive. The T allele and TT+TC genotype were associated with a reduced risk of developing SAD (T allele: odds ratio [OR] = 0.541, 95% confidence interval [CI] = 0.368–0.859, p = 0.005; TT+TC genotype: OR = 0.613, 95% CI = 0.315–0.725, p = 0.012). There was no statistically significant difference in allele and genotype frequencies between patients with SAD and control subjects for the A2M I1000V polymorphism, even after stratification by age of onset, gender, and APOE ε4 status. We found an interaction between LRP1 and APOE genotypes (p = 0.001), but no interaction between LRP1 and A2M genotypes. Our results suggest that the T allele of the LRP1 C766T polymorphism is associated with a decreased risk of SAD in APOE ε4 carriers from the Northern Han Chinese population.     

Effects of gender and dementia severity on Alzheimer's disease caregivers' sleep and biomarkers of coagulation and inflammation

Background: Being a caregiver for a spouse with Alzheimer’s disease is associated with increased risk for cardiovascular illness, particularly for males. This study examined the effects of caregiver gender and severity of the spouse’s dementia on sleep, coagulation, and inflammation in the caregiver.Methods: Eighty-one male and female spousal caregivers and 41 non-caregivers participated (mean age of all participants 70.2 years). Full-night polysomnography (PSG) was recorded in each participants home. Severity of the Alzheimer’s disease patient’s dementia was determined by the Clinical Dementia Rating (CDR) scale. The Role Overload scale was completed as an assessment of caregiving stress. Blood was drawn to assess circulating levels of D-dimer and Interleukin-6 (IL-6).Results: Male caregivers who were caring for a spouse with moderate to severe dementia spent significantly more time awake after sleep onset than female caregivers caring for spouses with moderate to severe dementia (p = .011), who spent a similar amount of time awake after sleep onset to caregivers of low dementia spouses and to non-caregivers. Similarly, male caregivers caring for spouses with worse dementia had significantly higher circulating levels of D-dimer (p = .034) than females caring for spouses with worse dementia. In multiple regression analysis (adjusted R² = .270, p < .001), elevated D-dimer levels were predicted by a combination of the CDR rating of the patient (p = .047) as well as greater time awake after sleep onset (p = .046).Discussion: The findings suggest that males caring for spouses with more severe dementia experience more disturbed sleep and have greater coagulation, the latter being associated with the disturbed sleep. These findings may provide insight into why male caregivers of spouses with Alzheimer’s disease are at increased risk for illness, particularly cardiovascular disease.     

Immune profiling of Alzheimer patients

Alzheimer's disease (AD) is characterized by extracellular senile plaques in the brain, containing amyloid-β peptide (Aβ). We identify immunological differences between AD patients and age-matched controls greater than those related to age itself. The biggest differences were in the CD4 + rather than the CD8 + T cell compartment resulting in lower proportions of naïve cells, more late-differentiated cells and higher percentages of activated CD4 + CD25 + T cells without a Treg phenotype in AD patients. Changes to CD4 + cells might be the result of chronic stimulation by Aβ present in the blood. These findings have implications for diagnosis and understanding the aetiology of the disease.     

rs2070424 of the SOD1 gene is associated with risk of Alzheimer's disease

ObjectiveOxidative stress plays an important role in Alzheimer's disease (AD) etiopathogenesis. There were several studies that showed impaired antioxidant defense system (ADS) enzymes expression or activity in AD patients. There are only few studies evaluating the importance of ADS gene single nucleotide polymorphisms (SNPs) as risk factors of AD. We evaluated association between chosen SNPs of the enzymes of the ADS and risk of AD.MethodsWe included 400 AD patients and 402 healthy controls. We studied rs1041740, rs4998557 and rs2070424 of the SOD1 gene, rs2855116, rs5746136 and rs4880 of the SOD2 gene and rs3448, rs1050450 and rs1800668 of the GPx-1 gene (real time PCR). To determine the APOE gene common polymorphism, two single-nucleotide polymorphisms (SNPs; NCBI SNPs rs429358 and rs7412) were genotyped (TaqMan assays, Applied Biosystems [ABI], Foster City, CA, USA). The genotype and gender frequencies were compared between the studied groups by the χ² test and mean age by the t-Student test.ResultsAmong all studied SNPs only rs2070424 of the SOD1 gene was a protective factor for AD in an additive (OR = 0.47; 95% CI = 0.30–0.74, p = 0.001) and recessive (OR = 0.47; 95% CI = 0.30–0.75, p = 0.002) models including age, gender and APOE gene status.Conclusionsrs2070424 polymorphism of the SOD1 gene is a risk factor for AD in Polish population. Allel G and genotype AG and GG are protective factors for AD.     

The effect of schooling on reported age of onset of cognitive decline: A collaborative study

Higher education has been reported to be a protective factor against dementia. We suggest that the strength of a risk factor may be measured by the length of time by which it delays disease onset; therefore, we examined whether people with lower education develop cognitive decline at an earlier age than people with more schooling. The study population was based on patients referred to our Memory Clinics from 1994 to 2004. Analysis of covariance was used to evaluate the effect of schooling on the reported age of memory decline, in patients with mild cognitive impairment (MCI) and in patients diagnosed with Alzheimer’s disease (AD). The mean reported age of onset of cognitive decline was unexpectedly lower in patients with higher education than in patients with fewer schooling years, with a relatively small effect size (beta = −0.6), and the effect was more marked in the MCI group. Every year of schooling advanced the reported age of onset by 6 months among patients with MCI (t = −6.18, p < .001) and by 3 months among patients with AD (t = −2.4, p = 0.017). Education may affect the reported age of onset of cognitive decline, but its magnitude is small. It is possible that increased awareness in more educated people leads them to consult earlier; this could explain the paradoxical finding of earlier reported age of onset of cognitive decline in patients with higher education.     

Arg972 insulin receptor substrate-1 polymorphism and risk and severity of Alzheimer’s disease

We explored the association between the Arg972 insulin receptor substrate-1 (IRS1) polymorphism and the risk and severity of Alzheimer’s disease (AD). We genotyped the Arg972 IRS1 (rs1801278) polymorphism in 1123 pairs of age, sex, body mass index, residence area and education level-matched Han Chinese AD patients and controls. AD severity was assessed with Mini-Mental State Examination (MMSE) scores. The AA (homozygous Arg972 IRS1) and GA (heterozygous Arg972 IRS1) genotypes were associated with an increased risk of AD after adjustment for comorbidities including type 2 diabetes mellitus, coronary heart disease, and hypertension (p < 0.001; adjusted odds ratio [OR] 3.93 and 2.90, respectively). The A allele was associated with an increased risk of AD after adjustment for comorbidities (p < 0.001; adjusted OR 2.26; 95% confidence interval 1.92–2.80). The percentage of Arg972 IRS1 AA homozygotes was higher in the MMSE score ⩽14 category than in the MMSE score 15–26 category overall and in each age group (p < 0.001), while the wild type IRS1 GG homozygotes were predominantly found in the MMSE score 15–26 category overall and in each age group. The GG homozygote group had higher MMSE score than the GA heterozygote group, which in turn had higher MMSE score than the AA homozygote group overall and in each age group (p < 0.05). In conclusion, the Arg972 IRS1 polymorphism is an independent risk factor for AD and the A allele has a gene dosage effect on AD severity in Han Chinese. This study adds fresh insights into the pathogenesis of AD.