Małgorzata Chodakowska-Żebrowska

Mutations in presenilin 1, presenilin 2 and amyloid precursor protein genes in patients with early-onset Alzheimer's disease in Poland

Mutations in three causative genes have been identified in patients with an autosomal-dominant form of early-onset Alzheimers disease (EOAD). To determine the spectrum of mutations in a group consisting of 40 Polish patients with clinically diagnosed familial EOAD and 1 patient with mild cognitive impairment (MCI) and family history of AD, we performed a screening for mutations in the presenilin 1 (PSEN1), presenilin 2 (PSEN2) and amyloid precursor protein (APP) genes. Four previously recognized pathogenic mutations in PSEN1 gene (H163R, M139V) and APP gene (T714A, V715A), and three novel putative mutations in PSEN1 gene (P117R and I213F) and PSEN2 gene (Q228L) were identified. The 34 patients with no mutations detected were older than the patients with mutations. A frequency of APOE4 allele was higher in this group. Frequency of mutations is relatively low (17%), possibly due to used operational definition of a patient with familial EOAD (a patient having at least one relative with early-onset dementia). It could be concluded that screening for mutations in the three genes could be included in a diagnostic program directed at patients with a positive family history or age of onset before 55 years.

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 Alzheimers 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.

A Novel MAPT Mutation, G55R, in a Frontotemporal Dementia Patient Leads to Altered Tau Function

Over two dozen mutations in the gene encoding the microtubule associated protein tau cause a variety of neurodegenerative dementias known as tauopathies, including frontotemporal dementia (FTD), PSP, CBD and Picks disease. The vast majority of these mutations map to the C-terminal region of tau possessing microtubule assembly and microtubule dynamics regulatory activities as well as the ability to promote pathological tau aggregation. Here, we describe a novel and non-conservative tau mutation (G55R) mapping to an alternatively spliced exon encoding part of the N-terminal region of the protein in a patient with the behavioral variant of FTD. Although less well understood than the C-terminal region of tau, the N-terminal region can influence both MT mediated effects as well as tau aggregation. The mutation changes an uncharged glycine to a basic arginine in the midst of a highly conserved and very acidic region. In vitro, 4-repeat G55R tau nucleates microtubule assembly more effectively than wild-type 4-repeat tau; surprisingly, this effect is tau isoform specific and is not observed in a 3-repeat G55R tau versus 3-repeat wild-type tau comparison. In contrast, the G55R mutation has no effect upon the abilities of tau to regulate MT growing and shortening dynamics or to aggregate. Additionally, the mutation has no effect upon kinesin translocation in a microtubule gliding assay. Together, (i) we have identified a novel tau mutation mapping to a mutation deficient region of the protein in a bvFTD patient, and (ii) the G55R mutation affects the ability of tau to nucleate microtubule assembly in vitro in a 4-repeat tau isoform specific manner. This altered capability could markedly affect in vivo microtubule function and neuronal cell biology. We consider G55R to be a candidate mutation for bvFTD since additional criteria required to establish causality are not yet available for assessment.

The E318G substitution in PSEN1 gene is not connected with Alzheimer's disease in a large Polish cohort

Mutations in the presenilin 1 (PSEN1) gene are known to cause nearly 50% of early-onset, familial Alzheimers disease (AD) cases. To determine whether E318G mutation is related causally to AD in the Polish population E318G mutation frequency was assessed using PCR-RFLP method in a total of 659 subjects: 256 AD patients, 210 healthy, age-matched control subjects, 100 Parkinsons disease patients and 93 centenarians. When the mutation frequencies were compared to healthy controls, no significant differences between the groups were found. It could be concluded that E318G mutation is not related causally to AD in the Polish population, either as a risk factor or a disease causing mutation.

Identification of a Late Onset Alzheimer's Disease Candidate Risk Variant at 9q21.33 in Polish Patients

Late onset Alzheimers disease (LOAD) accounts for about 95% of all Alzheimers disease cases. While the APOE ε4 variant seems to have unparalleled influence on increased LOAD risk, it does not explain all of the heritability of LOAD. In this study, we present the application of a cost-effective, pooled DNA genome-wide association study (GWAS) to uncover genetic risk variants associated with LOAD in Polish women diagnosed with either mild cognitive impairment (MCI) or well-defined LOAD. A group of 141 patients (94 LOAD and 47 MCI), as well as 141 controls, were assayed using Affymetrix Genome-Wide Human SNP 6.0 arrays. Allele frequency distributions were compared using χ(2)-tests, and significantly associated SNPs at p < 0.0001 with a proxy SNP were selected. GWAS marker selection was conducted using PLINK, and selected SNPs were validated on DNA samples from the same cohort using KASPar Assays. In addition, to determine the genotype of APOE variants (rs429358, rs7412), a multiplex tetra-primer amplification refractory mutation system was applied. The GWAS revealed nine SNPs associated with MCI and/or LOAD. Of these, the association of seven SNPs was confirmed by genotyping of individual patients. Furthermore, the APOE ε4 appeared to be a risk variant for LOAD, while the APOE ε3 showed a protective effect. Multivariate analysis showed association between rs7856774 and LOAD, independently from the effect of APOE variation. Pooled DNA GWAS enabled the identification of a novel LOAD candidate risk variant, rs7856774 (9q21.33), tagging a possible genomic enhancer affecting proximal transcribed elements including DAPK1 gene.

Association between Cerebrospinal Fluid Biomarkers for Alzheimer's Disease, APOE Genotypes and Auditory Verbal Learning Task in Subjective Cognitive Decline, Mild Cognitive Impairment, and Alzheimer's Disease

In the course of Alzheimers disease (AD), early pathological changes in the brain start decades before any clinical manifestation. The concentration levels of AD cerebrospinal fluid (CSF) biomarkers, such as amyloid-β1-42 (Aβ1-42), total tau (T-tau), and phosphorylated tau (P-tau), may reflect a cerebral pathology facilitating an early diagnosis of the disease and predicting a cognitive deterioration. The aim of this study was to estimate the prevalence of AD CSF biomarkers in those individuals with a subjective cognitive decline (SCD), a mild cognitive impairment (MCI), and Alzheimers dementia (AD-D), together with the relationships between the biomarkers, an APOE ɛ4 presence, and a verbal episodic memory performance. We included 252 patients from the memory clinic with a diagnosis of SCD (n = 85), MCI (n = 87), and AD-D (n = 80). A verbal episodic memory performance level was assessed and was based on a delayed recall trial from the 10-word list of an auditory verbal learning task (AVLT). We found that the patients with more severe cognitive impairments had significantly lower levels of Aβ1-42 and higher levels of T-tau and P-tau. This pattern was also typical for the APOE ɛ4 carriers, who had lower levels of Aβ1-42 than the noncarriers in the AD-D and MCI groups. The levels of T-tau and P-tau were significantly higher in the APOE ɛ4 carriers than in the noncarriers, but only in the MCI patients. The AVLT performance in the whole study samples was predicted by age, Aβ1-42, and the T-tau CSF biomarkers, but not by the APOE genotyping.