S. Engelborghs

Genome-wide association study indentifies variants at CLU and CR1 associated with Alzheimer’s disease

The gene encoding apolipoprotein E (APOE) on chromosome 19 is the only confirmed susceptibility locus for late-onset Alzheimers disease. To identify other risk loci, we conducted a large genome-wide association study of 2,032 individuals from France with Alzheimers disease (cases) and 5,328 controls. Markers outside APOE with suggestive evidence of association (P < 10−5) were examined in collections from Belgium, Finland, Italy and Spain totaling 3,978 Alzheimers disease cases and 3,297 controls. Two loci gave replicated evidence of association: one within CLU (also called APOJ), encoding clusterin or apolipoprotein J, on chromosome 8 (rs11136000, OR = 0.86, 95% CI 0.81–0.90, P = 7.5 × 10−9 for combined data) and the other within CR1, encoding the complement component (3b/4b) receptor 1, on chromosome 1 (rs6656401, OR = 1.21, 95% CI 1.14–1.29, P = 3.7 × 10−9 for combined data). Previous biological studies support roles of CLU and CR1 in the clearance of β amyloid (Aβ) peptide, the principal constituent of amyloid plaques, which are one of the major brain lesions of individuals with Alzheimers disease.

Genetic contribution of FUS to frontotemporal lobar degeneration

Background: Recently, the FUS gene was identified as a new causal gene for amyotrophic lateral sclerosis (ALS) in ∼4% of patients with familial ALS. Since ALS and frontotemporal lobar degeneration (FTLD) are part of a clinical, pathologic, and genetic disease spectrum, we investigated a potential role of FUS in FTLD. Methods: We performed mutational analysis of FUS in 122 patients with FTLD and 15 patients with FTLD-ALS, as well as in 47 patients with ALS. Mutation screening was performed by sequencing of PCR amplicons of the 15 FUS exons. Results: We identified 1 patient with FTLD with a novel missense mutation, M254V, that was absent in 638 control individuals. In silico analysis predicted this amino acid substitution to be pathogenic. The patient did not have a proven family history of neurodegenerative brain disease. Further, we observed the known R521H mutation in 1 patient with ALS. No FUS mutations were detected in the patients with FTLD-ALS. While insertions/deletions of 2 glycines (G) were suggested to be pathogenic in the initial FUS reports, we observed an identical GG-deletion in 2 healthy individuals and similar G-insertions/deletions in 4 other control individuals, suggesting that G-insertions/deletions within this G-rich region may be tolerated. Conclusions: In a first analysis of FUS in patients with frontotemporal lobar degeneration (FTLD), we identified a novel FUS missense mutation, M254V, in 1 patient with pure FTLD. At this point, the biologic relevance of this mutation remains elusive. Screening of additional FTLD patient cohorts will be needed to further elucidate the contribution of FUS mutations to FTLD pathogenesis.

Clinical heterogeneity in 3 unrelated families linked to VCP p.Arg159His

Background: Families associated with missense mutations in the valosin-containing protein (VCP) present with a rare autosomal dominant multisystem disorder of frontotemporal lobar degeneration (FTLD), inclusion body myopathy (IBM), and Paget disease of bone (PDB), referred to as IBMPFD. Methods: We used exon-based genomic DNA sequencing to test for VCP mutations in 123 unrelated Belgian patients with FTLD and their relatives, and the absence of such mutations in 157 control individuals. We analyzed haplotype sharing among mutation carriers by genotyping 8 microsatellite markers in the VCP locus. We obtained family history and clinical and pathologic data using established diagnostic instruments. Results: Mutation analysis of VCP identified 2 Belgian patients with FTLD carrying the p.Arg159His mutation, which segregated in their families. In one family, patients presented with FTLD only, whereas in the other family, patients developed FTLD, PDB, or both without signs of IBM for any of the mutation carriers. We had previously identified p.Arg159His in an Austrian family with patients exhibiting both IBM and PDB. Haplotype sharing analysis indicated that the 3 p.Arg159His families are unrelated. Clinical follow-up of the Austrian family identified dementia symptoms in 1 patient. Autopsy data of 3 patients of the 2 Belgian families revealed FTLD pathology with numerous ubiquitin-immunoreactive, intranuclear inclusions and dystrophic neurites staining positive for TDP-43 protein. Conclusions: In 3 unrelated families with IBMPFD segregating VCP p.Arg159His, we observed a high degree of clinical heterogeneity and variable penetrance of the 3 cardinal clinical phenotypes: inclusion body myopathy, Paget disease of bone, and frontotemporal lobar degeneration. In contrast, the neuropathologic phenotype was consistent with FTLD-TDP type 4.

The utility of α-synuclein as biofluid marker in neurodegenerative diseases: a systematic review of the literature

The discovery of α-synuclein (α-syn) as a major component of Lewy bodies, neuropathological hallmark of Parkinsons disease (PD), dementia with Lewy bodies and of glial inclusions in multiple system atrophy initiated the investigation of α-syn as a biomarker in cerebrospinal fluid (CSF). Due to the involvement of the periphery in PD the quantification of α-syn in peripheral fluids such as serum, plasma and saliva has been investigated as well. We review how the development of multiple assays for the quantification of α-syn has yielded novel insights into the variety of α-syn species present in the different fluids; the optimal preanalytical conditions required for robust quantification and the potential clinical value of α-syn as biomarker. We also suggest future approaches to use of CSF α-syn in neurodegenerative diseases.

Progranulin variability has no major role in Parkinson disease genetic etiology

Background: Different loss-of-function mutations were identified underlying PGRN haploinsufficiency in patients with frontotemporal lobar degeneration. PGRN mutations were also identified in other neurodegenerative brain diseases such as amyotrophic lateral sclerosis and Alzheimer disease, though their biologic contribution to these diseases remains elusive. Because of its apparent role in neuronal survival, we argued that PGRN might also contribute to Parkinson disease (PD) pathogenesis. Methods: We screened PGRN exons for mutations in 255 patients with PD and 459 control individuals by direct genomic sequencing. Genetic association of PGRN with risk for PD was assessed using single nucleotide polymorphisms (SNPs) across the gene. Results: In patients we identified four missense mutations of which p.Asp33Glu and p.Arg514Met were absent in control individuals. Single SNP and haplotype analyses did not detect significant associations with PD. Conclusions: Our results do not support a major role for PGRN in the genetic etiology of Parkinson disease (PD). At this stage and in the absence of functional data, it remains unclear whether p.Asp33Glu and p.Arg514Met are biologically relevant to PD pathogenesis in the mutation carriers.

P2-142: Diagnostic performance of a CSF-biomarker panel in 100 autopsy-confirmed dementia cases as analyzed with single and multiparameter tests

when the disease is at its earliest stages. There are a few CSF biomarkers for AD but their sensitivity and specificity have limited clinical application. Therefore, identification of new and better biomarkers, especially those that could identify AD at its earliest stages will greatly aid us in AD prevention, diagnosis and treatment. Objective(s): To identify new CSF biomarkers for mild AD. Methods: We took a comparative proteomics approach by analyzing the proteomes of 12 CSF samples: 6 from subjects that have mild AD (CDR 1) and 6 from age-matched controls (CDR 0). A pooled sample was made that consisted of an aliquot from each of the 12 samples. After being depleted of high abundant proteins, these CSF samples were analyzed with 2D-DIGE. Each gel had a CSF sample from a subject that was CDR 0 and CDR1 as well as the pooled sample. A subset of protein spots were matched across all gels. MS/MS analyses were performed to identify spots that displayed differential abundance between the two CDR groups. The identified proteins include ones that have already been reported to be changed in AD CSF and/or implicated in AD pathogenesis (e.g. 1-antichymotrypsin (ACT), gelsolin) as well as a number of novel candidates. A few of these candidate biomarkers were selected for validation using ELISA. Their expression levels were first validated using the original 12 CSF samples and then with a much larger sample set that contained CDR 0 (n 55), 0.5 (n 20) and 1(n 17) CSF samples. The levels of two proteins were found to be significantly elevated in the AD vs. control group. Interestingly, their protein levels correlate with each other but do not correlate with that of CSF A 42, a biomarker for amyloid deposition. Validation studies on more candidates are underway. Conclusions: We have identified new CSF candidate biomarkers using novel proteomics approaches and also validated these candidates in a larger sample set. The orthogonal nature of the changes in some biomarker candidates to the existing AD biomarker A 42 suggests additional utility as part of a new protein biomarker panel.