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

Patient with PSEN1 Glu318Gly and Other Possible Disease Risk Mutations, Diagnosed with Early Onset Alzheimer's Disease

In this manuscript, we introduced a French EOAD patient in Korea who carried the presenilin-1 (PSEN1) Glu318Gly mutations with four possible risk variants, including sortilin-related receptor 1 (SORL1) Glu270Lys, ATP-binding cassette subfamily A member 7 (ABCA7) Val1946Met, translocase of outer mitochondrial membrane 40 (TOMM40) Arg239Trp, and granulin (GRN) Ala505Gly. The patient started to present memory decline and behavioral dysfunction in his early 60s. His brain imaging presented amyloid deposits by positron emission tomography (PET-CT). The multimer detection system (MDS) screening test for plasma for amyloid oligomers was also positive, which supported the AD diagnosis. It was verified that PSEN1 Glu318Gly itself may not impact amyloid production. However, additional variants were found in other AD and non-AD risk genes, as follows: SORL1 Glu270Lys was suggested as a risk mutation for AD and could increase amyloid peptide production and impair endosome functions. ABCA7 Val1946Met was a novel variant that was predicted to be damaging. The GRN Ala505Gly was a variant with uncertain significance; however, it may reduce the granulin levels in the plasma of dementia patients. Pathway analysis revealed that PSEN1 Glu318Gly may work as a risk factor along with the SORL1 and ABCA7 variants since pathway analysis revealed that PSEN1 could directly interact with them through amyloid-related and lipid metabolism pathways. TOMM40 and PSEN1 could have common mechanisms through mitochondrial dysfunction. It may be possible that PSEN1 Glu318Gly and GRN Ala505Gly would impact disease by impairing immune-related pathways, including microglia and astrocyte development, or NFkB-related pathways. Taken together, the five risk factors may contribute to disease-related pathways, including amyloid and lipid metabolism, or impair immune mechanisms.

Study of Alzheimer's disease- and frontotemporal dementia-associated genes in the Cretan Aging Cohort

Using exome sequencing, we analyzed 196 participants of the Cretan Aging Cohort (CAC; 95 with Alzheimer's disease [AD], 20 with mild cognitive impairment [MCI], and 81 cognitively normal controls). The APOE ε4 allele was more common in AD patients (23.2%) than in controls (7.4%; p < 0.01) and the PSEN2 p.Arg29His and p.Cys391Arg variants were found in 3 AD and 1 MCI patient, respectively. Also, we found the frontotemporal dementia (FTD)-associated TARDBP gene p.Ile383Val variant in 2 elderly patients diagnosed with AD and in 2 patients, non CAC members, with the amyotrophic lateral sclerosis/FTD phenotype. Furthermore, the p.Ser498Ala variant in the positively selected GLUD2 gene was less frequent in AD patients (2.11%) than in controls (16%; p < 0.01), suggesting a possible protective effect. While the same trend was found in another local replication cohort (n = 406) and in section of the ADNI cohort (n = 808), this finding did not reach statistical significance and therefore it should be considered preliminary. Our results attest to the value of genetic testing to study aged adults with AD phenotype.

Evaluation of the Clinical Features Accompanied by the Gene Mutations: The 2 Novel PSEN1 Variants in a Turkish Early-onset Alzheimer Disease Cohort

INTRODUCTION

Early-onset Alzheimer disease (EOAD) is an earlier Alzheimer disease form which is characterized by the mutations in the amyloid precursor protein, presenilin-1/2 (PSEN1/2), and triggering receptor expressed on myeloid cells 2 (TREM2). However, it is still necessary to report mutational screening in multiethnic groups to improve the genetic background of EOAD due to the variant classification challenge.

METHODS

We performed targeted sequencing for the amyloid precursor protein, PSEN1, PSEN2, and TREM2 genes in 74 patients and 1 family diagnosed with EOAD.

RESULTS

Among the detected variants, 8 were coding and 6 were noncoding in 15 of 74 patients. In PSEN1, 2 pathogenic coding variants (T274K and L364P) detected in 2 patients were novel and 3 coding variants (G183V, E318G, and L219P) detected in 2 patients were previously reported. We found 4 patients with the compound heterozygosity for the PSEN2 A23= and N43= and a family with the coexistence of them, and 1 patient with TREM2 Y38C. The coding variation frequency was 12.1%. In silico analysis indicated pathogenic potentials and clinical interpretations of the detected variants.

CONCLUSION

Our study reveals the rare gene variants including novel ones from the Turkish EOAD cohort and provides to clinicians the list of detected variants in the screened genes, which may also be useful for accurate genetic counseling.

Asymptomatic Carriers of Presenilin-1 E318G Variant Show no Cerebrospinal Fluid Biochemical Signs Suggestive of Alzheimer's disease in a Family with Late-onset Dementia

BACKGROUND

Presenilin-1 (PSEN-1) is a component of the γ-secretase complex involved in β-amyloid Precursor Protein (AβPP) processing. Usually, Alzheimer's disease (AD)-linked mutations in the PSEN-1 gene lead to the early onset and increase the production of the aggregation-prone peptide Aβ42. However, the PSEN-1 E318G variant has an unclear pathogenic role and is recently reported as a genetic risk factor for AD. In particular, E318G variant presence correlated with increased cerebrospinal fluid (CSF) levels of Total Tau (t-tau) and Phosphorylated Tau (p-tau).

OBJECTIVE

We describe a large Italian family, which we followed from January 2003 to January 2018, with the late-onset AD and the E318G variant, with the aim of assessing E318G-associated CSF or plasma biochemical changes in biomarkers of dementia.

METHOD

CSF Aβ42, t-tau and p-tau, plasma Aβ42 and Aβ40 were assessed by ELISA tests, while CSF amyloid peptides profile was investigated by mass spectrometry.

RESULTS

We did not find any changes in CSF biochemical markers (Aβ42, t-tau, p-tau and amyloid peptides) of asymptomatic E318G carriers in 2010 and 2012, but plasma Aβ40 was increased at the same times. From 2003 to 2018, no asymptomatic E318G carrier developed AD.

CONCLUSION

Our follow-up of this family may help elucidate E318G's role in AD and globally points to a null effect of this variant.

PSEN1 gene polymorphisms in Caucasian Alzheimer's disease: A meta-analysis

BACKGROUND

A meta-analysis was performed to assess PSEN1 gene polymorphisms (rs1800839 and rs17125721) in Alzheimer's disease (AD) risk.

METHODS

A systematic electronic search was performed across databases to retrieve studies published before 31 January 2017. The association between the selected PSEN1 polymorphisms and AD was based on five genetic models using DerSimonian and Laird's method or Mantel-Haenszel's method.

RESULTS

A total of 14 case-controlled studies were included. Results showed that rs1800839 polymorphism was significantly associated with AD in allelic OR=0.85 (95% CI [0.72-1.00]) and dominant OR=0.82 (95% CI [0.69-0.98]) genetic models, respectively. However, an insignificant association was found for rs17125721 polymorphism in all genetic models.

CONCLUSIONS

Meta-analysis of PSEN1 gene suggests that the rs1800839 polymorphism has potential influence on AD among Caucasians.

Influence of low frequency PSEN1 variants on familial Alzheimer's disease risk in Brazil

About 30-70% of familial Alzheimer's disease (AD) cases are related to mutations in presenilin-1 gene (PSEN1). Although the role of mutations and common variants in AD had been extensively investigated, the contribution of rare or low frequency PSEN1 variants on AD risk remains unclear. In the current study, we performed a mutational screening of PSEN1 coding exons and flanking intronic sequences among 53 index cases with familial history of AD from Rio de Janeiro (Brazil). Two missense variants (rs63750592; rs17125721), one rare and a low frequency variant, and two intronic variants (rs3025786; rs165932) were identified. In silico tools were used to predict the functional impact of the variants, revealing no changes in protein functionality by exonic variants. Otherwise, all variants were predicted to alter splicing signals. Prediction results, together with previous reports, suggest a correlation between rs17125721 and AD. So, a subsequent case-control study to evaluate the role of rs1712572 on AD risk was performed in an additional sample of 120 AD sporadic cases and in 149 elderly healthy controls by TaqMan Genotyping Assay. Our data indicates a risk association for rs17125721 in familial AD cases (OR=6.0; IC95%=1.06-33.79; p=0.042). In addition, we tested the multiplicative interaction between allele ε4 of the apolipoprotein E (APOE) and rs17125721 and no statistical association was found. Taken together, our findings provide new insight about the genetic relevance of low frequency PSEN1 variants for familial AD development.

Atypical Huntington's disease with the clinical presentation of behavioural variant of frontotemporal dementia

Huntington's disease is an incurable, adult-onset, autosomal dominant inherited disorder caused by an expanded trinucleotide repeat (CAG). In this study, we describe a Huntington's disease patient displaying clinical symptoms of the behavioural variant of frontotemporal dementia in the absence of tremor and ataxia. The clinical onset was at the age of 36 years and the disease progressed slowly (18 years). Genetic testing revealed expanded trinucleotide CAG repeats in the Huntingtin gene, together with a Glu318Gly polymorphism in presenilin 1. Neuropathological assessment revealed extensive amyloid β (Aβ) aggregates in all cortical regions. No inclusions displaying hyperphosphorylated tau or phosphorylated transactive response DNA-binding protein 43 (TDP43) were found. A high number of p62 (sequestosome 1) immunopositive intranuclear inclusions were seen mainly in the cortex, while subcortical areas were affected to a lesser extent. Confocal microscopy revealed that the majority of p62 intranuclear lesions co-localised with the fused-in-sarcoma protein (FUS) immunostaining. The morphology of the inclusions resembled intranuclear aggregates in Huntington's disease. The presented proband suffered from Huntington's disease showed atypical distribution of FUS positive intranuclear aggregates in the cortical areas with concomitant Alzheimer's disease pathology.

Presenilin-1 mutation E318G and familial Alzheimer's disease in the Italian population

Presenilin-1 (PSEN-1) is a component of the gamma-secretase complex involved in beta-amyloid precursor protein (betaAPP) processing. To date about 140 pathogenic mutations in the PSEN-1 gene have been identified and their main biochemical effect is to increase the production of the fibrillogenic peptide Abeta(1-42). An exception is the PSEN-1 [E318G] mutation that does not alter Abeta(1-42) generation and is generally considered a non-pathogenic polymorphism. Nevertheless, this mutation was reported to be a genetic risk factor for familial Alzheimer's disease (FAD) in the Australian population. To independently confirm this indication, we performed a case-control association study in the Italian population. We found a significant association (p<0.05, Fisher's exact test) between the presence of PSEN-1 [E318G] and FAD. In addition, on measuring the Abeta(1-42) and Abeta(1-40) concentrations in fibroblast-conditioned media cultured from PSEN-1 [E318G] carriers and PSEN-1 [wild type] controls we noted a significant decrease (p<0.05, Mann-Whitney test) in the Abeta(1-42)/Abeta(1-40) ratio in PSEN-1 [E318G] carriers, suggesting a peculiar biochemical effect of this mutation.

Familial Alzheimer's disease presenilin 1 mutations cause alterations in the conformation of presenilin and interactions with amyloid precursor protein

Presenilin 1 (PS1) is a critical component of the gamma-secretase complex, an enzymatic activity that cleaves amyloid beta (Abeta) from the amyloid precursor protein (APP). More than 100 mutations spread throughout the PS1 molecule are linked to autosomal dominant familial Alzheimer's disease (FAD). All of these mutations lead to a similar phenotype: an increased ratio of Abeta42 to Abeta40, increased plaque deposition, and early age of onset. We use a recently developed microscopy approach, fluorescence lifetime imaging microscopy, to monitor the relative molecular distance between PS1 N and C termini in intact cells. We show that FAD-linked missense mutations located near the N and C termini, in the mid-region of PS1, and the exon 9 deletion mutation all change the spatial relationship between PS1 N and C termini in a similar way, increasing proximity of the two epitopes. This effect is opposite of that observed by treatment with Abeta42-lowering nonsteroidal anti-inflammatory drugs (NSAIDs) (Lleo et al., 2004b). Accordingly, treatment of M146L PS1-overexpressing neurons with high-dose NSAIDs somewhat offsets the conformational change associated with the mutation. Moreover, by monitoring the relative distance between a PS1 loop epitope and the APP C terminus, we demonstrate that the FAD PS1 mutations are also associated with a consistent change in the configuration of the PS1-APP complex. The nonpathogenic E318G PS1 polymorphism had no effect on PS1 N terminus-C terminus proximity or PS1-APP interactions. We propose that the conformational change we observed may therefore provide a shared molecular mechanism for FAD pathogenesis caused by a wide range of PS1 mutations.