Association of MAPT haplotype-tagging polymorphisms with cerebrospinal fluid biomarkers of Alzheimer's disease: A preliminary study in a Croatian cohort

Total tau in cerebrospinal fluid detects treatment responders among spinal muscular atrophy types 1-3 patients treated with nusinersen

AIMS

Considering the substantial variability in treatment response across patients with spinal muscular atrophy (SMA), reliable markers for monitoring response to therapy and predicting treatment responders need to be identified. The study aimed to determine if measured concentrations of disease biomarkers (total tau protein, neurofilament light chain, and S100B protein) correlate with the duration of nusinersen treatment and with scores obtained using functional scales for the assessment of motor abilities.

METHODS

A total of 30 subjects with SMA treated with nusinersen between 2017 and 2021 at the Department of Pediatrics, University Hospital Centre Zagreb, Croatia, were included in this study. Cerebrospinal fluid (CSF) samples were collected by lumbar puncture prior to intrathecal application of nusinersen. Protein concentrations in CSF samples were determined by enzyme-linked immunosorbent assay in 26 subjects. The motor functions were assessed using functional motor scales.

RESULTS

The main finding was significantly decreased total tau correlating with the number of nusinersen doses and motor improvement in the first 18-24 months of treatment (in all SMA patients and SMA type 1 patients). Neurofilament light chain and S100B were not significantly changed after administration of nusinersen.

CONCLUSIONS

The measurement of total tau concentration in CSF is a reliable index for monitoring the biomarker and clinical response to nusinersen therapy in patients with SMA.

Navigating the ALS Genetic Labyrinth: The Role of MAPT Haplotypes

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by wide clinical and biological heterogeneity, with a large proportion of ALS patients also exhibiting frontotemporal dementia (FTD) spectrum symptoms. This project aimed to characterize risk subtypes of the H1 haplotype within the MAPT (microtubule-associated protein tau) gene, according to their possible effect as a risk factor and as a modifying factor in relation to the age of disease onset. One hundred patients from Bulgaria with sporadic ALS were genotyped for the variants rs1467967, rs242557, rs1800547, rs3785883, rs2471738, and rs7521. Haploview 4.2 and SHEsisPlus were used to reconstruct haplotype frequencies using genotyping data from the 1000 Genomes project as controls. Genotype-phenotype correlation was investigated in the context of age of disease onset and risk of disease development. While the individual variants of the subtypes do not influence the age of onset of the disease, a correlation was found between the specific haplotype GGAGCA (H1b) and the risk of developing sALS, with results showing that individuals harboring this haplotype have a nearly two-fold increased risk of developing sALS compared to other H1 subtypes. The results from this study suggest that fine transcriptional regulation at the MAPT locus can influence the risk of ALS.

Serotonin Receptor Gene Polymorphisms Are Associated with Cerebrospinal Fluid, Genetic, and Neuropsychological Biomarkers of Alzheimer's Disease

A decrease in serotonergic transmission throughout the brain is among the earliest pathological changes in Alzheimer's disease (AD). Serotonergic receptors are also affected in AD. Polymorphisms in genes of serotonin (5HT) receptors have been mostly associated with behavioral and psychological symptoms of dementia (BPSD). In this study, we examined if AD patients carrying different genotypes in 5HTR1B rs13212041, 5HTR2A rs6313 (T102C), 5HTR2C rs3813929 (-759C/T), and 5HTR6 rs1805054 (C267T) polymorphisms have a higher risk of faster disease progression (assessed by neuropsychological testing), are more prone to develop AD-related pathology (reflected by levels of cerebrospinal fluid [CSF] AD biomarkers), or have an association with an apolipoprotein E (APOE) haplotype. This study included 115 patients with AD, 53 patients with mild cognitive impairment (MCI), and 2701 healthy controls. AD biomarkers were determined in the CSF of AD and MCI patients using enzyme-linked immunosorbent assays (ELISA), while polymorphisms were determined using either TaqMan SNP Genotyping Assays or Illumina genotyping platforms. We detected a significant decrease in the CSF amyloid β1-42 (Aβ1-42) and an increase in p-tau181/Aβ1-42 ratio in carriers of the T allele in the 5HTR2C rs3813929 (-759C/T) polymorphism. A significantly higher number of APOE ε4 allele carriers was observed among individuals carrying a TT genotype within the 5HTR2A T102C polymorphism, a C allele within the 5HTR1B rs13212041 polymorphism, and a T allele within the 5HTR6 rs1805054 (C267T) polymorphism. Additionally, individuals carrying the C allele within the 5HTR1B rs13212041 polymorphism were significantly more represented among AD patients and had poorer performances on the Rey-Osterrieth test. Carriers of the T allele within the 5HTR6 rs1805054 had poorer performances on the MMSE and ADAS-Cog. As all four analyzed polymorphisms of serotonin receptor genes showed an association with either genetic, CSF, or neuropsychological biomarkers of AD, they deserve further investigation as potential early genetic biomarkers of AD.

Association between H2 haplotype of microtubule associated protein tau gene (deletion / insertion) with Alzheimer Disease in Tunisian patients

It is widely recognized that Alzheimer's disease (AD) is the main cause of dementia in the elderly. AD is typically characterized by the extraneuronal plaque made up essentially of the amyloid β peptide and intraneuronal tangles of hyperphosphorylated microtubule-associated Tau protein. This study investigates the possible interaction between AD and the deletion/insertion polymorphism in intron 9 of the Tau gene haplotype and APOE state in a Tunisian AD cases population (n = 85) and control (n = 91). The H2/H2 genotype was higher in the AD group as compared to the controls (22.4% vs. 7.8%). The frequency of H2 allele is higher in the patients group, and the difference of allele frequency is statistically significant between the two groups (χ2 = 12.220, p < 0.05). H2 allele is correlated with the female gender within the patient group (χ2 = 7.649, p = 0.006) Tau H2 haplotype can be identified as a risk factor of AD in the studied Tunisian population and was associated to female gender. There is no significant correlation between the frequency of Tau gene ins/del polymorphism and cognitive profile distribution in the patient group (p > 0.05).

Neurodegeneration and Glial Activation Related CSF Biomarker as the Diagnosis of Alzheimer's Disease: A Systematic Review and an Updated Meta-analysis

OBJECTIVE

Recently, neuron specific enolase (NSE), Visinin-like protein-1 (VLP-1), neurogranin (Ng), and YKL-40 have been identified as candidates for neuronal degeneration and glial activation biomarkers. Therefore, we perform a comprehensive meta-analysis to assess the diagnostic value of CSF NSE, VLP-1, Ng and YKL-40 in Alzheimer's disease (AD).

METHODS

We searched Pubmed, MEDLINE, EMBASE databases for research about the levels of CSF NSE, VLP-1, Ng and YKL-40 in AD patients compared with controls or other dementia diseases until Dec 2020.

RESULTS

The present meta-analysis contained a total of 51 studies comprising 6248 patients with dementia disorders and 3861 controls. Among them, there were 3262 patients with AD, 2456 patients with mild cognitive impairment (MCI), 173 patients with vascular dementia (VaD), 221 patients with frontotemporal dementia (FTD), and 136 with Lewy bodies dementia (DLB). Our study demonstrated that CSF NSE, VLP-1, Ng and YKL-40 levels were increased in AD as compared to healthy controls. We also observed that the CSF NSE level was higher in AD than VaD, suggesting CSF NSE might act as a key role in distinguishing between AD and VaD. Interestingly, there was a higher VLP-1 expression in AD, and a lower expression in DLB patients. Moreover, we found the CSF Ng level was increased in AD than MCI, implying CSF Ng might be a biomarker for identifying the progression of AD. Additionally, a significantly higher CSF YKL-40 level was detected not only in AD, but also in FTD, DLB, VaD, signifying YKL-40 was not sensitive in the diagnosis of AD.

CONCLUSION

Our study confirmed that CSF levels of NSE, VLP-1, and Ng could be valuable biomarkers for identifying patients who are more susceptible to AD and distinguishing AD from other neurodegenerative dementia disorders.

Tau and MAPT genetics in tauopathies and synucleinopathies

MAPT encodes the microtubule-associated protein tau, which is the main component of neurofibrillary tangles (NFTs) and found in other protein aggregates. These aggregates are among the pathological hallmarks of primary tauopathies such as frontotemporal dementia (FTD). Abnormal tau can also be observed in secondary tauopathies such as Alzheimer's disease (AD) and synucleinopathies such as Parkinson's disease (PD). On top of pathological findings, genetic data also links MAPT to these disorders. MAPT variations are a cause or risk factors for many tauopathies and synucleinopathies and are associated with certain clinical and pathological features in affected individuals. In addition to clinical, pathological, and genetic overlap, evidence also suggests that tau and alpha-synuclein may interact on the molecular level, and thus might collaborate in the neurodegenerative process. Understanding the role of MAPT variations in tauopathies and synucleinopathies is therefore essential to elucidate the role of tau in the pathogenesis and phenotype of those disorders, and ultimately to develop targeted therapies. In this review, we describe the role of MAPT genetic variations in tauopathies and synucleinopathies, several genotype-phenotype and pathological features, and discuss their implications for the classification and treatment of those disorders.

Transcriptomic signatures of treatment response to the combination of escitalopram and memantine or placebo in late-life depression

Drugs that target glutamate neuronal transmission, such as memantine, offer a novel approach to the treatment of late-life depression, which is frequently comorbid with cognitive impairment. The results of our recently published double-blind, randomized, placebo-controlled trial of escitalopram or escitalopram/memantine in late-life depression with subjective memory complaints (NCT01902004) indicated no differences between treatments in depression remission, but additional benefits in cognition at 12-month follow-up with combination treatment. To identify pathways and biological functions uniquely induced by combination treatment that may explain cognitive improvements, we generated transcriptional profiles of remission compared with non-remission from whole blood samples. Remitters to escitalopram compared with escitalopram/memantine combination treatment display unique patterns of gene expression at baseline and 6 months after treatment initiation. Functional enrichment analysis demonstrates that escitalopram-based remission associates to functions related to cellular proliferation, apoptosis, and inflammatory response. Escitalopram/memantine-based remission, however, is characterized by processes related to cellular clearance, metabolism, and cytoskeletal dynamics. Both treatments modulate inflammatory responses, albeit via different effector pathways. Additional research is needed to understand the implications of these results in explaining the observed superior effects of combination treatment on cognition observed with prolonged treatment.

The effects of genotype on inflammatory response in hippocampal progenitor cells: A computational approach

Cell culture models are valuable tools to study biological mechanisms underlying health and disease in a controlled environment. Although their genotype influences their phenotype, subtle genetic variations in cell lines are rarely characterised and taken into account for in vitro studies. To investigate how the genetic makeup of a cell line might affect the cellular response to inflammation, we characterised the single nucleotide variants (SNPs) relevant to inflammation-related genes in an established hippocampal progenitor cell line (HPC0A07/03C) that is frequently used as an in vitro model for hippocampal neurogenesis (HN). SNPs were identified using a genotyping array, and genes associated with chronic inflammatory and neuroinflammatory response gene ontology terms were retrieved using the AmiGO application. SNPs associated with these genes were then extracted from the genotyping dataset, for which a literature search was conducted, yielding relevant research articles for a total of 17 SNPs. Of these variants, 10 were found to potentially affect hippocampal neurogenesis whereby a majority (n=7) is likely to reduce neurogenesis under inflammatory conditions. Taken together, the existing literature seems to suggest that all stages of hippocampal neurogenesis could be negatively affected due to the genetic makeup in HPC0A07/03C cells under inflammation. Additional experiments will be needed to validate these specific findings in a laboratory setting. However, this computational approach already confirms that in vitro studies in general should control for cell lines subtle genetic variations which could mask or exacerbate findings.

The role of frontotemporal dementia associated genes in patients with Alzheimer's disease

Alzheimer's disease (AD) and frontotemporal dementia (FTD) overlap clinically and pathologically. However, the role of FTD-associated genes in patients with AD remained unclear. To explore the relationship between FTD-associated genes and AD risk, we investigated 14 FTD-associated genes via targeted next-generation sequencing panel or whole-genome sequencing in a total of 721 AD patients and 1391 controls. Common variant-based association analysis and gene-based association test of rare variants were performed by PLINK 1.9 and Sequence Kernel Association Test-Optimal (SKAT-O test) respectively. As a result, 2 common variants, UBQLN1 rs1044175 (p value = 2.76 × 10^-4) and MAPT rs2258689 (p value = 5.71 × 10^-4), differed significantly between AD patients and controls. Additionally, gene-based analysis aggregating rare variants demonstrated that HNRNPA1 reached statistical significance in the SKAT-O test (p value = 2.24 × 10^-3). Protein-protein interaction analysis showed that UBQLN1, MAPT, and HNRNPA1 interacted with proteins encoded by well-recognized AD-associated genes. Our study indicated that UBQLN1, MAPT, and HNRNPA1 are implicated in the pathogenesis of AD in the mainland Chinese population.

IL-1β, IL-6, IL-10, and TNFα Single Nucleotide Polymorphisms in Human Influence the Susceptibility to Alzheimer's Disease Pathology

BACKGROUND

Neuroinflammation plays an important role in Alzheimer's disease (AD). During this process, activated microglia release pro-inflammatory cytokines such as interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor α (TNFα) that participate in neuron damage, but also anti-inflammatory cytokines (such as IL-10), which maintain homeostasis of immune response. Previous studies showed the association of IL-1α -889C/T (rs1800587), IL-1β-1473G/C (rs1143623), IL-6 -174C/G (rs1800795), IL-10 -1082G/A (rs1800896), and TNFα -308A/G (rs1800629) polymorphisms with AD.

OBJECTIVE

We aimed to investigate whether people with certain IL-1α, IL-1β, IL-6, IL-10, and TNFα genotypes in these polymorphisms are more prone to develop AD-related pathology, reflected by pathological levels of cerebrospinal fluid (CSF) AD biomarkers including amyloid-β1-42, total tau (t-tau), tau phosphorylated at Thr 181 (p-tau181), Ser 199 (p-tau199), and Thr 231 (p-tau231), and visinin-like protein 1 (VILIP-1).

METHODS

The study included 115 AD patients, 53 patients with mild cognitive impairment, and 11 healthy controls. The polymorphisms were determined using real-time polymerase chain reaction. Levels of CSF biomarkers were determined by enzyme-linked immunosorbent assay.

RESULTS

A significant increase in p-tau CSF levels was found in patients with the AA IL-10 -1082G/A and GG TNFα -308A/G genotypes, and in carriers of a G allele in IL-1β -1473C/G and IL-6 -174C/G polymorphisms. t-tau levels were increased in carriers of a G allele in IL-1β -1473C/G polymorphism. An increase in VILIP-1 levels was observed in patients with CG and GG IL-1β -1473C/G, GC IL-6 -174C/G, and GG TNFα -308A/G genotype.

CONCLUSION

These results suggest that persons carrying certain genotypes in IL10 (-1082G/A), IL1β (1473C/G), IL6 (-174C/G), and TNFIα (-308A/G) could be more vulnerable to development of neuroinflammation, and consequently of AD.

Relationships of Cerebrospinal Fluid Alzheimer's Disease Biomarkers and COMT, DBH, and MAOB Single Nucleotide Polymorphisms

The noradrenergic and dopaminergic systems are affected in Alzheimer’s disease (AD). Polymorphisms in genes encoding enzymes and proteins that are components of these systems can affect products of transcription and translation and lead to altered enzymatic activity and alterations in overall dopamine and noradrenaline levels. Catechol-O-methyltransferase (COMT) and monoamine oxidase B (MAOB) are the enzymes that regulate degradation of dopamine, while dopamine β-hydroxylase (DBH) is involved in synthesis of noradrenaline. COMT Val158Met (rs4680), DBH rs1611115 (also called –1021C/T or –970C/T), and MAOB rs1799836 (also called A644G) polymorphisms have been previously associated with AD. We assessed whether these polymorphisms are associated with cerebrospinal fluid (CSF) AD biomarkers including total tau (t-tau), phosphorylated tau proteins (p-tau₁₈₁, p-tau₁₉₉, and p-tau₂₃₁), amyloid-β₄₂ (Aβ₄₂), and visinin-like protein 1 (VILIP-1) to test possible relationships of specific genotypes and pathological levels of CSF AD biomarkers. The study included 233 subjects: 115 AD, 53 mild cognitive impairment, 54 subjects with other primary causes of dementia, and 11 healthy controls. Significant decrease in Aβ₄₂ levels was found in patients with GG compared to AG COMT Val158Met genotype, while t-tau and p-tau₁₈₁ levels were increased in patients with AA compared to AG COMT Val158Met genotype. Aβ₄₂ levels were also decreased in carriers of A allele in MAO-B rs1799836 polymorphism, while p-tau₁₈₁ levels were increased in carriers of T allele in DBH rs1611115 polymorphism. These results indicate that COMT Val158Met, DBH rs1611115, and MAOB rs1799836 polymorphisms deserve further investigation as genetic markers of AD.

A meta-analysis on the levels of VILIP-1 in the CSF of Alzheimer's disease compared to normal controls and other neurodegenerative conditions

Alzheimer's disease (AD) is a progressing neurodegenerative disorder and the main cause of serious irreversible cognitive decline in elderly people. Visinin-like protein 1 (VILIP-1) is a member of the family of calcium-binding proteins and plays a crucial role in AD pathophysiology. Multiple studies have shown that CSF levels of VILIP-1 are increased in AD patients compared to normal controls, or other neurodegenerative conditions. We searched online databases for studies on the levels of VILIP-1 in the CSF of AD patients in comparison to normal controls, mild cognitive impairment (MCI) patients and Dementia with Lewy bodies (DLB) patients. A total of ten studies were used for the comparison between AD and controls, three studies for the comparison between AD and MCI, two studies for AD and DLB and two studies for the comparison between stable MCI and MCI progressed to AD. We found that VILIP-1 levels are significantly higher in AD compared to normal controls, but not to the other groups, and furthermore, they are significantly higher in patient with MCI progressed to AD, than in stable MCI patients.

Comprehensive Integrative Analyses Identify TIGD5 rs75547282 as a Risk Variant for Autism Spectrum Disorder

Although recent genome-wide association studies have identified risk loci that strongly associates with autism spectrum disorder (ASD), how to pinpoint the causal genes remains a challenge. We aimed to pinpoint the potential causal genes and explore the possible susceptibility and mechanism. A convergent functional genomics (CFG) method was used to prioritize the candidate genes by combining lines of evidence, including Sherlock analysis, spatio-temporal expression patterns, expression analysis, protein-protein interactions, co-expression and association with brain structure. A higher score in the CFG approach suggested that more evidence supported this gene as an ASD risk gene. We screened genes with higher CFG scores for candidate functional single nucleotide polymorphisms (SNPs). A genotyping experiment (602 ASD children and 604 healthy sex-matched children) and the dual-luciferase reporter gene assay were followed to validate the effects of SNPs. We identified three genes (MAPT, ZNF285, and TIGD5) as candidate causal genes using the CFG approach. The genotyping experiment showed that TIGD5 rs75547282 was associated with an increased risk of ASD under the dominant model (OR = 1.37, 95% CI = 1.09-1.72, P = 0.006) though the statistical power was limited (5.2%). The T allele of rs75547282 activated the expression of TIGD5 compared with the C allele in the dual-luciferase reporter assay. Our study indicates that such comprehensive integrative analyses may be an effective way to explore promising ASD susceptibility variants and needs to be further investigated in future research. Genotyping experiments should, however, be based on a larger population sample to increase statistical power. LAY SUMMARY: We set out to pinpoint the potential causal genes of ASD and explore the possible susceptibility and mechanism by combining lines of evidence from different analyses. Our results show that TIGD5 rs75547282 is associated with the risk of ASD in the Han Chinese population. In addition, a similar framework to seek promising ASD risk variants could be further investigated in future research Autism Res 2021, 14: 631-644. © 2021 International Society for Autism Research and Wiley Periodicals LLC.

Novel tau biomarkers phosphorylated at T181, T217 or T231 rise in the initial stages of the preclinical Alzheimer's continuum when only subtle changes in Aβ pathology are detected

In Alzheimer's disease (AD), tau phosphorylation in the brain and its subsequent release into cerebrospinal fluid (CSF) and blood is a dynamic process that changes during disease evolution. The main aim of our study was to characterize the pattern of changes in phosphorylated tau (p-tau) in the preclinical stage of the Alzheimer's continuum. We measured three novel CSF p-tau biomarkers, phosphorylated at threonine-181 and threonine-217 with an N-terminal partner antibody and at threonine-231 with a mid-region partner antibody. These were compared with an automated mid-region p-tau181 assay (Elecsys) as the gold standard p-tau measure. We demonstrate that these novel p-tau biomarkers increase more prominently in preclinical Alzheimer, when only subtle changes of amyloid-β (Aβ) pathology are detected, and can accurately differentiate Aβ-positive from Aβ-negative cognitively unimpaired individuals. Moreover, we show that the novel plasma N-terminal p-tau181 biomarker is mildly but significantly increased in the preclinical stage. Our results support the idea that early changes in neuronal tau metabolism in preclinical Alzheimer, likely in response to Aβ exposure, can be detected with these novel p-tau assays.

Neurogranin and VILIP-1 as Molecular Indicators of Neurodegeneration in Alzheimer's Disease: A Systematic Review and Meta-Analysis

Neurogranin (Ng) and visinin-like protein 1 (VILIP-1) are promising candidates for Alzheimer's Disease (AD) biomarkers closely related to synaptic and neuronal degeneration. Both proteins are involved in calcium-mediated pathways. The meta-analysis was performed in random effects based on the ratio of means (RoM) with calculated pooled effect size. The diagnostic utility of these proteins was examined in cerebrospinal fluid (CSF) of patients in different stages of AD compared to control (CTRL). Ng concentration was also checked in various groups with positive (+) and negative (-) amyloid beta (Aβ). Ng highest levels of RoM were observed in the AD (n = 1894) compared to CTRL (n = 2051) group (RoM: 1.62). Similarly, the VILIP-1 highest values of RoM were detected in the AD (n = 706) compared to CTRL (n = 862) group (RoM: 1.34). Concentrations of both proteins increased in more advanced stages of AD. However, Ng seems to be an earlier biomarker for the assessment of cognitive impairment. Ng appears to be related with amyloid beta, and the highest levels of Ng in CSF was observed in the group with pathological Aβ+ status. Our meta-analysis confirms that Ng and VILIP-1 can be useful CSF biomarkers in differential diagnosis and monitoring progression of cognitive decline. Although, an additional advantage of the protein concentration Ng is the possibility of using it to predict the risk of developing cognitive impairment in normal controls with pathological levels of Aβ1-42. Analyses in larger cohorts are needed, particularly concerning Aβ status.

Variants in PPP2R2B and IGF2BP3 are associated with higher tau deposition

Tau deposition is a key biological feature of Alzheimer’s disease that is closely related to cognitive impairment. However, it remains poorly understood why certain individuals may be more susceptible to tau deposition while others are more resistant. The recent availability of in vivo assessment of tau burden through positron emission tomography provides an opportunity to test the hypothesis that common genetic variants may influence tau deposition. We performed a genome-wide association study of tau-positron emission tomography on a sample of 754 individuals over age 50 (mean age 72.4 years, 54.6% men, 87.6% cognitively unimpaired) from the population-based Mayo Clinic Study of Aging. Linear regression was performed to test nucleotide polymorphism associations with AV-1451 (¹⁸F-flortaucipir) tau-positron emission tomography burden in an Alzheimer’s-signature composite region of interest, using an additive genetic model and covarying for age, sex and genetic principal components. Genome-wide significant associations with higher tau were identified for rs76752255 (P = 9.91 × 10⁻⁹, β = 0.20) in the tau phosphorylation regulatory gene PPP2R2B (protein phosphatase 2 regulatory subunit B) and for rs117402302 (P  = 4.00 × 10⁻⁸, β = 0.19) near IGF2BP3 (insulin-like growth factor 2 mRNA-binding protein 3). The PPP2R2B association remained genome-wide significant after additionally covarying for global amyloid burden and cerebrovascular disease risk, while the IGF2BP3 association was partially attenuated after accounting for amyloid load. In addition to these discoveries, three single nucleotide polymorphisms within MAPT (microtubule-associated protein tau) displayed nominal associations with tau-positron emission tomography burden, and the association of the APOE (apolipoprotein E) ɛ4 allele with tau-positron emission tomography was marginally nonsignificant (P  = 0.06, β = 0.07). No associations with tau-positron emission tomography burden were identified for other single nucleotide polymorphisms associated with Alzheimer’s disease clinical diagnosis in prior large case–control studies. Our findings nominate PPP2R2B and IGF2BP3 as novel potential influences on tau pathology which warrant further functional characterization. Our data are also supportive of previous literature on the associations of MAPT genetic variation with tau, and more broadly supports the inference that tau accumulation may have a genetic architecture distinct from known Alzheimer’s susceptibility genes, which may have implications for improved risk stratification and therapeutic targeting.

The MAPT H1 Haplotype Is a Risk Factor for Alzheimer's Disease in APOE ε4 Non-carriers

An ancestral inversion of 900 kb on chromosome 17q21, which includes the microtubule-associated protein tau (MAPT) gene, defines two haplotype clades in Caucasians (H1 and H2). The H1 haplotype has been linked inconsistently with AD. In a previous study, we showed that an SNP tagging this haplotype (rs1800547) was associated with AD risk in a large population from the Dementia Genetics Spanish Consortium (DEGESCO) including 4435 cases and 6147 controls. The association was mainly driven by individuals that were non-carriers of the APOE ε4 allele. Our aim was to replicate our previous findings in an independent sample of 4124 AD cases and 3290 controls from Spain (GR@ACE project) and to analyze the effect of the H1 sub-haplotype structure on the risk of AD. The H1 haplotype was associated with AD risk (OR = 1.12; p = 0.0025). Stratification analysis showed that this association was mainly driven by the APOE ε4 non-carriers (OR = 1.15; p = 0.0022). Pooled analysis of both Spanish datasets (n = 17,996) showed that the highest AD risk related to the MAPT H1/H2 haplotype was in those individuals that were the oldest [third tertile (>77 years)] and did not carry APOE ε4 allele (p = 0.001). We did not find a significant association between H1 sub-haplotypes and AD. H1c was nominally associated but lost statistical significance after adjusting by population sub-structure. Our results are consistent with the hypothesis that genetic variants linked to the MAPT H1/H2 are tracking a genuine risk allele for AD. The fact that this association is stronger in APOE ε4 non-carriers partially explains previous controversial results and might be related to a slower alternative causal pathway less dependent on brain amyloid load.

Role of Microglial Cells in Alzheimer's Disease Tau Propagation

Uncontrolled immune response in the brain contributes to the progression of all neurodegenerative disease, including Alzheimer's disease (AD). Recent investigations have documented the prion-like features of tau protein and the involvement of microglial changes with tau pathology. While it is still unclear what sequence of events is causal, it is likely that tau seeding potential and microglial contribution to tau propagation act together, and are essential for the development and progression of degenerative changes. Based on available evidence, targeting tau seeds and controlling some signaling pathways in a complex inflammation process could represent a possible new therapeutic approach for treating neurodegenerative diseases. Recent findings propose novel diagnostic assays and markers that may be used together with standard methods to complete and improve the diagnosis and classification of these diseases. In conclusion, a novel perspective on microglia-tau relations reveals new issues to investigate and imposes different approaches for developing therapeutic strategies for AD.

Association of MAPT haplotype-tagging polymorphisms with cerebrospinal fluid biomarkers of Alzheimer's disease: A preliminary study in a Croatian cohort

INTRODUCTION

Alzheimer's disease (AD) is the world leading cause of dementia. Early detection of AD is essential for faster and more efficacious usage of therapeutics and preventive measures. Even though it is well known that one ε4 allele of apolipoprotein E gene increases the risk for sporadic AD five times, and that two ε4 alleles increase the risk 20 times, reliable genetic markers for AD are not yet available. Previous studies have shown that microtubule-associated protein tau (MAPT) gene polymorphisms could be associated with increased risk for AD.

METHODS

The present study included 113 AD patients and 53 patients with mild cognitive impairment (MCI), as well as nine healthy controls (HC) and 53 patients with other primary causes of dementia. The study assessed whether six MAPT haplotype-tagging polymorphisms (rs1467967, rs242557, rs3785883, rs2471738, del-In9, and rs7521) and MAPT haplotypes are associated with AD pathology, as measured by cerebrospinal fluid (CSF) AD biomarkers amyloid β1-42 (Aβ1-42 ), total tau (t-tau), tau phosphorylated at epitopes 181 (p-tau181 ), 199 (p-tau199 ), and 231 (p-tau231 ), and visinin-like protein 1 (VILIP-1).

RESULTS

Significant increases in t-tau and p-tau CSF levels were found in patients with AG and AA MAPT rs1467967 genotype, CC MAPT rs2471738 genotype and in patients with H1H2 or H2H2 MAPT haplotype.

CONCLUSIONS

These results indicate that MAPT haplotype-tagging polymorphisms and MAPT haplotypes should be further tested as potential genetic biomarkers of AD.