17q21.31 duplication causes prominent tau-related dementia with increased MAPT expression.

To assess the role of rare copy number variations in Alzheimer's disease (AD), we conducted a case-control study using whole-exome sequencing data from 522 early-onset cases and 584 controls. The most recurrent rearrangement was a 17q21.31 microduplication, overlapping the CRHR1, MAPT, STH and KANSL1 genes that was found in four cases, including one de novo rearrangement, and was absent in controls. The increased MAPT gene dosage led to a 1.6-1.9-fold expression of the MAPT messenger RNA. Clinical signs, neuroimaging and cerebrospinal fluid biomarker profiles were consistent with an AD diagnosis in MAPT duplication carriers. However, amyloid positon emission tomography (PET) imaging, performed in three patients, was negative. Analysis of an additional case with neuropathological examination confirmed that the MAPT duplication causes a complex tauopathy, including prominent neurofibrillary tangle pathology in the medial temporal lobe without amyloid-ß deposits. 17q21.31 duplication is the genetic basis of a novel entity marked by prominent tauopathy, leading to early-onset dementia with an AD clinical phenotype. This entity could account for a proportion of probable AD cases with negative amyloid PET imaging recently identified in large clinical series.

Alzheimer disease: modeling an Aß-centered biological network.

In genetically complex diseases, the search for missing heritability is focusing on rare variants with large effect. Thanks to next generation sequencing technologies, genome-wide characterization of these variants is now feasible in every individual. However, a lesson from current studies is that collapsing rare variants at the gene level is often insufficient to obtain a statistically significant signal in case-control studies, and that network-based analyses are an attractive complement to classical approaches. In Alzheimer disease (AD), according to the prevalent amyloid cascade hypothesis, the pathology is driven by the amyloid beta (Aß) peptide. In past years, based on experimental studies, several hundreds of proteins have been shown to interfere with Aß production, clearance, aggregation or toxicity. Thanks to a manual curation of the literature, we identified 335 genes/proteins involved in this biological network and classified them according to their cellular function. The complete list of genes, or its subcomponents, will be of interest in ongoing AD genetic studies.

SORL1 rare variants: a major risk factor for familial early-onset Alzheimer's disease.

The SORL1 protein plays a protective role against the secretion of the amyloid ß peptide, a key event in the pathogeny of Alzheimer's disease. We assessed the impact of SORL1 rare variants in early-onset Alzheimer's disease (EOAD) in a case-control setting. We conducted a whole exome analysis among 484 French EOAD patients and 498 ethnically matched controls. After collapsing rare variants (minor allele frequency ≤1%), we detected an enrichment of disruptive and predicted damaging missense SORL1 variants in cases (odds radio (OR)=5.03, 95% confidence interval (CI)=(2.02-14.99), P=7.49.10(-5)). This enrichment was even stronger when restricting the analysis to the 205 cases with a positive family history (OR=8.86, 95% CI=(3.35-27.31), P=3.82.10(-7)). We conclude that predicted damaging rare SORL1 variants are a strong risk factor for EOAD and that the association signal is mainly driven by cases with positive family history.

De novo deleterious genetic variations target a biological network centered on Aß peptide in early-onset Alzheimer disease.

We hypothesized that de novo variants (DNV) might participate in the genetic determinism of sporadic early-onset Alzheimer disease (EOAD, onset before 65 years). We investigated 14 sporadic EOAD trios first by array-comparative genomic hybridization. Two patients carried a de novo copy number variation (CNV). We then performed whole-exome sequencing in the 12 remaining trios and identified 12 non-synonymous DNVs in six patients. The two de novo CNVs (an amyloid precursor protein (APP) duplication and a BACE2 intronic deletion) and 3/12 non-synonymous DNVs (in PSEN1, VPS35 and MARK4) targeted genes from a biological network centered on the Amyloid beta (Aß) peptide. We showed that this a priori-defined genetic network was significantly enriched in amino acid-altering DNV, compared with the rest of the exome. The causality of the APP de novo duplication (which is the first reported one) was obvious. In addition, we provided evidence of the functional impact of the following three non-synonymous DNVs targeting this network: the novel PSEN1 variant resulted in exon 9 skipping in patient's RNA, leading to a pathogenic missense at exons 8-10 junction; the VPS35 missense variant led to partial loss of retromer function, which may impact neuronal APP trafficking and Aß secretion; and the MARK4 multiple nucleotide variant resulted into increased Tau phosphorylation, which may trigger enhanced Aß-induced toxicity. Despite the difficulty to recruit Alzheimer disease (AD) trios owing to age structures of the pedigrees and the genetic heterogeneity of the disease, this strategy allowed us to highlight the role of de novo pathogenic events, the putative involvement of new genes in AD genetics and the key role of Aß network alteration in AD.

High frequency of potentially pathogenic SORL1 mutations in autosomal dominant early-onset Alzheimer disease.

Performing exome sequencing in 14 autosomal dominant early-onset Alzheimer disease (ADEOAD) index cases without mutation on known genes (amyloid precursor protein (APP), presenilin1 (PSEN1) and presenilin2 (PSEN2)), we found that in five patients, the SORL1 gene harbored unknown nonsense (n=1) or missense (n=4) mutations. These mutations were not retrieved in 1500 controls of same ethnic origin. In a replication sample, including 15 ADEOAD cases, 2 unknown non-synonymous mutations (1 missense, 1 nonsense) were retrieved, thus yielding to a total of 7/29 unknown mutations in the combined sample. Using in silico predictions, we conclude that these seven private mutations are likely to have a pathogenic effect. SORL1 encodes the Sortilin-related receptor LR11/SorLA, a protein involved in the control of amyloid beta peptide production. Our results suggest that besides the involvement of the APP and PSEN genes, further genetic heterogeneity, involving another gene of the same pathway is present in ADEOAD.

Establishment of induced pluripotent stem cells IRMBi005-A from a patient with sporadic Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurological disorder and the most common form of dementia worldwide. Sporadic Alzheimer's disease (sAD) cases are the main forms, over 95% of AD cases, but still poorly understood. Thereby there is a crucial need to develop in vitro models for studying this multifactorial disorder. Here, we report the reprogramming of skin fibroblasts from a 57-years-old male donor. The new generated iPSC cell line has a normal karyotype and, is pluripotent since it demonstrates the ability to differentiate in vitro into the three germ layers. This iPSC line will be used to understand pathological mechanisms of sAD.

Generation of induced pluripotent stem cell lines IRMBi003-A and IRMBi003-B from a healthy donor to model Alzheimer's disease.

Induced Pluripotent Stem Cell (iPSC) lines derived from healthy individuals are helpful and essential tools for disease modelling. Here, we described the reprogramming of skin fibroblasts obtained from a healthy 59-year-old individual without Alzheimer's disease. The generated iPSC lines have a normal karyotype, expressed pluripotency markers, and demonstrated the ability to differentiate into the three germ layers. The iPSC lines will be used as controls to study Alzheimer's disease mechanisms.

Generation of induced pluripotent stem cells (IRMBi001-A) from an Alzheimer's disease patient carrying a G217D mutation in the PSEN1 gene.

Induced pluripotent stem cells (iPSC) were generated from skin fibroblasts obtained from a 50 year-old patient suffering from Alzheimer's disease and carrying a G217D causal mutation on presenilin 1 (PSEN1). iPSCs were obtained following reprogramming using the integration-free Sendai Virus system which allows expression of the Yamanaka factors. Verification of their pluripotency was achieved by demonstrating the expression of pluripotency markers and their differentiation potential into the three primary germ layers. iPS cells carry the patient G217D mutation and present a normal karyotype. The reported PS1-G217D iPSC line may be used to model and study human AD pathology in vitro.

Generation of induced pluripotent stem cells (iPSCs) IRMBi002-A from an Alzheimer's disease patient carrying a D694N mutation in the APP gene.

Induced pluripotent stem cells (iPSC) were generated from skin fibroblasts obtained from a 58 year-old woman suffering from Alzheimer's disease and carrying a D694N mutation on Amyloid precursor protein (APP). Fibroblasts were reprogrammed into iPSC using the integration-free Sendai Virus which allows the expression of the Yamanaka factors. Verification of their pluripotency was achieved by demonstrating the expression of pluripotency markers and their differentiation potential into the three primary germ layers. The cells have the corresponding mutation and present a normal karyotype. The reported APP-D694N iPSC line may be used to model and study human AD pathology in vitro.

Variations in the APP gene promoter region and risk of Alzheimer disease.

We genotyped five polymorphisms, including two polymorphisms with known effects on transcriptional activity, in a large cohort of 427 Alzheimer disease (AD) cases and 472 control subjects. An association between rs463946 (-3102 G/C) and AD was found and was confirmed in a replication sample of a similar size. By contrast, analysis of three recently described rare mutations influencing APP transcription did not confirm their association with AD risk.