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Dementie met Lewy Bodies (DLB) is na de ziekte van Alzheimer (AD) de meest voorkomende dementie op oudere leeftijd. Er is bij DLB veel overlap met symptomen die bij zowel AD als de ziekte van Parkinson (PD) voorkomen. De diagnose wordt daardoor dan ook vaak laat gesteld. De oorzaken van DLB zijn nog onvoldoende bekend en biomarkers om de diagnose vroeg te stellen ontbreken vooralsnog. Om meer duidelijkheid te krijgen over ziektemechanismen bij DLB onderzoeken we genen en eiwitten bij patiënten met een erfelijke vorm van DLB. We doen dit door met nieuwe technieken van erfelijkheidsonderzoek (exome sequencing) en eiwitstudies (proteomics) in hersenvocht en hersenweefsel naar veranderde genen en eiwitten te kijken.

Resultaten
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resultaten uit de genetische en proteomics analyse van het hersenvocht worden momenteel uitgewerkt in verschillende artikelen en worden na publicatie gedeeld.

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Background

Dementia with Lewy Bodies (DLB) is the second most common dementia after Alzheimer’s Disease in the elderly. Recognizing DLB remains challenging due to the highly variable clinical presentation (varying from cognitive fluctuations, parkinsonism, hallucinations, to sleep disorders) and considerable overlap with AD and Parkinson’s Disease (PD). The early diagnosis is further hampered by the lack of cerebrospinal fluid (CSF) and genetic biomarkers. As a consequence, DLB is diagnosed on average 3 years after symptom-onset, a year later than AD. Differentiation from other dementias is clinically relevant, because of a high sensitivity for cholinesterase inhibitor therapy and to avoid the detrimental effects of antipsychotics in DLB.

 

Aggregation of dementia and PD in families with DLB suggests that genetic susceptibility plays an important role. However, the genetic and molecular mechanisms are still poorly understood. The presence of alpha-synuclein (SNCA) in Lewy Bodies (LBs) is considered the neuropathological hallmark of DLB. Yet, pure LB pathology accounts for only 20-30% of clinical DLB cases and mutations in the SNCA gene account for a minority of familial DLB. Further, SNCA in CSF is neither a sensitive nor specific biomarker for DLB. Two proteomic studies reported numerous other proteins in LBs and CSF of DLB cases that are potentially relevant in the etiology of DLB. Taken together, these findings suggest that other genes and molecular mechanisms are involved.

 

Previous genetic studies had several methodological shortcomings, being either small, heterogeneous, or lacking pathological confirmation of DLB cases. Due to the overlap in clinical symptoms between AD and DLB, it is likely that these studies also included AD cases. In addition, the number of patients in DLB families is usually too small for classical linkage studies. Further, linkage studies are of limited value when causal variants in several genes are expected (genetic heterogeneity) or in the case of a variable clinical presentation (phenotypic heterogeneity), both of which are important in DLB. Whole exome sequencing (WES) is a novel genetic technique used to selectively sequence the coding regions of the genome, which has proven successful in identifying functional variation in small families and in genetical and phenotypical heterogeneous disorders. Our consortium has recently shown that WES is promising in particular when using proteomics in parallel, by finding the genetic defect and corresponding mutant protein in a family with dementia and parkinsonism due to familial neurofilamentopathy.

 

Main objective

to identify novel biomarkers to improve the early diagnosis of DLB.

 

Aims

1. to identify proteins that potentially serve as novel biomarker in DLB using brain tissue (Lewy bodies) and cerebrospinal fluid proteomics in patients with familial and pathological proven DLB.

 

2. to identify novel genetic factors in familial DLB using whole exome sequencing in several families with (pathological proven) DLB.

 

Approach

1.Quantitative tissue proteomics

Microlaser dissection and mass spectrometry will be performed in brain tissue of 12 probable DLB cases with a positive family history for DLB or PD selected from a clinico-pathological cohort. Cases are selected based on a high Braak DLB stage of 5 or 6. Those with a Braak AD stage of 3 or higher or other major neuropathology are excluded. Over 1000 Lewy bodies from 2 regions of 12 brains of DLB cases will be excised for mass spectrometry to study novel proteins that may serve as putative biomarkers. The same regions of 12 cases without neurological disease will be used as reference.

 

2.Quantitative CSF proteomics

CSF proteomics will be performed in 20 DLB cases from a large ongoing academic outpatient memory clinic of whom CSF is available. To improve homogeneity of cases, the study will be limited to DLB cases with a positive family history for PD or dementia in at least one first-degree relative and a normal CSF AD profile (normal AmyloidBeta1-42, tau and p-tau). Twenty elderly patients with subjective memory complaints (and normal brain imaging and neuropsychological examinations) serve as a reference. The CSF proteome of DLB patients and control subjects will be compared by a label-free proteomics workflow based on depletion-gel-nanoLC-MS/MS, to identify differentially expressed proteins in DLB and controls. For initial validation of novel candidate biomarkers, we will apply immunological assays for a subset of five identified candidate biomarkers.

 

3. Genetic studies using WES in familial and pathological-proven DLB

WES will be performed in 10 DLB families from several outpatient memory clinics, in whom at least 2 first-degree relatives are affected with either DLB or PD and in one healthy elderly control in whom DNA is available. In addition, WES will be performed in 20 pathological proven cases with familial DLB selected from a clinico-pathological cohort.

 

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