Next‐generation sequencing in the diagnosis of Dementia and Huntington’s disease Phenocopy Syndromes

Dementia is a major cause of disability worldwide, especially in the elderly. While Mendelian causes of dementia only account for a small proportion of cases, their role in elucidating the pathophysiology has been paramount. Genetically defined cohorts also offer opportunities for trials of disease‐modifying treatments, even before the onset of symptoms. Previously, only a small number of genes could be selected for genetic testing because of cost‐restrictions, but the advent of next‐generation sequencing has enabled its more widespread use. This thesis explored the use of next‐generation sequencing in patients living with dementia and HD phenocopy (HDPC) syndromes, who include patients with mixed presentations of dementia and motor symptoms. Using a validated 17 gene Dementia Gene panel supplemented by C9orf72 expansion testing and Apolipoprotein (ApoE) genotyping in over 3000 patients and controls, I determined the success rate of genetic panel testing in dementia; I developed an algorithm for the selection of patients for genetic testing based on the clinical presentation and common predictors of genetic causes of dementia. A detailed analysis of the ApoE data in the frontotemporal dementia cohort revealed strong effects of ApoE4 on age at onset in the subset with proven or suspected tau neuropathology, as well as opposite effects of amyloid‐beta pathology. In order to improve the definition and diagnostic rate of HDPC syndromes, patients who were referred for HD testing from two clinics were compared based on their clinical presentation; patients could not be distinguished based on clinical presentation alone, even if analysed as patterns. Given the low success rate of dementia gene panel testing in the HDPC cohort, 50 patients were selected for whole‐genome sequencing based on their HD‐likeness and their likelihood of harbouring a Mendelian variant. The results revealed a number of variants of interest but require replication

Predictors for a dementia gene mutation based on gene-panel next-generation sequencing of a large dementia referral series

Next-generation genetic sequencing (NGS) technologies facilitate the screening of multiple genes linked to neurodegenerative dementia, but there are few reports about their use in clinical practice. Which patients would most profit from testing, and information on the likelihood of discovery of a causal variant in a clinical syndrome, are conspicuously absent from the literature, mostly for a lack of large-scale studies. We applied a validated NGS dementia panel to 3241 patients with dementia and healthy aged controls; 13,152 variants were classified by likelihood of pathogenicity. We identified 354 deleterious variants (DV, 12.6% of patients); 39 were novel DVs. Age at clinical onset, clinical syndrome and family history each strongly predict the likelihood of finding a DV, but healthcare setting and gender did not. DVs were frequently found in genes not usually associated with the clinical syndrome. Patients recruited from primary referral centres were compared with those seen at higher-level research centres and a national clinical neurogenetic laboratory; rates of discovery were comparable, making selection bias unlikely and the results generalisable to clinical practice. We estimated penetrance of DVs using large-scale online genomic population databases and found 71 with evidence of reduced penetrance. Two DVs in the same patient were found more frequently than expected. These data should provide a basis for more informed counselling and clinical decision making

Genetic testing in dementia — utility and clinical strategies

Techniques for clinical genetic testing in dementia disorders have advanced rapidly but remain to be more widely implemented in practice. A positive genetic test offers a precise molecular diagnosis, can help members of an affected family to determine personal risk, provides a basis for reproductive choices and can offer options for clinical trials. The likelihood of identifying a specific genetic cause of dementia depends on the clinical condition, the age at onset and family history. Attempts to match phenotypes to single genes are mostly inadvisable owing to clinical overlap between the dementias, genetic heterogeneity, pleiotropy and concurrent mutations. Currently, the appropriate genetic test in most cases of dementia is a next-generation sequencing gene panel, though some conditions necessitate specific types of test such as repeat expansion testing. Whole-exome and whole-genome sequencing are becoming financially feasible but raise or exacerbate complex issues such as variants of uncertain significance, secondary findings and the potential for re-analysis in light of new information. However, the capacity for data analysis and counselling is already restricting the provision of genetic testing. Patients and their relatives need to be given reliable information to enable them to make informed choices about tests, treatments and data sharing; the ability of patients with dementia to make decisions must be considered when providing this information

Micro-milling work-holding devices employing adhesive forces

IngenieursweseBedryfsingenieursweseMicro-parts are often very fragile rendering conventional, mechanical work-holding fixtures unsuitable for them since they exert large straining forces. Furthermore, macroworkholding devices occupy a large space which impedes high precision required in micromilling. Although some micro-clamping fixtures exist, they are limited to specific part shapes and in most cases expensive to manufacture. Hence this paper focuses on the application of adhesive forces namely electrostatic, surface tension and van-der-Waals forces; in work-holding strategies for micro-milling operations. An analysis is given as to their applicability with reference to micro-milling cutting forces

A sensor skid for precise 3d modeling of production lines

ABSTRACT: Motivated by the increasing need of rapid characterization of environments in 3D, we designed and built a sensor skid that automates the work of an operator of terrestrial laser scanners. The system combines terrestrial laser scanning with kinematic laser scanning and uses a novel semi-rigid SLAM method. It enables us to digitize factory environments without the need to stop production. The acquired 3D point clouds are precise and suitable to detect objects that collide with items moved along the production line

A novel presenilin 1 duplication mutation (Ile168dup) causing Alzheimer's disease associated with myoclonus, seizures and pyramidal features

Mutations in the Presenilin 1 (PSEN1) gene are the most common cause of autosomal dominant familial Alzheimer's disease. We report the clinical, imaging and postmortem findings of kindred carrying a novel duplication mutation (Ile168dup) in the PSEN1 gene. We interpret the pathogenicity of this novel variant and discuss the additional neurological features (pyramidal dysfunction, myoclonus and seizures) that accompanied cognitive decline. This report broadens the clinical phenotype of PSEN1 insertion mutations while also highlighting the importance of considering duplication, insertion and deletion mutations in cases of young onset dementia

Evaluating the causality of novel sequence variants in the prion protein gene by example

The estimation of pathogenicity and penetrance of novel prion protein gene (PRNP) variants presents significant challenges, particularly in the absence of family history, which precludes the application of Mendelian segregation. Moreover, the ambiguities of prion disease pathophysiology renders conventional in silico predictions inconclusive. Here, we describe 2 patients with rapid cognitive decline progressing to akinetic mutism and death within 10 weeks of symptom onset, both of whom possessed the novel T201S variant in PRNP. Clinically, both satisfied diagnostic criteria for probable sporadic Creutzfeldt-Jakob disease and in one, the diagnosis was confirmed by neuropathology. While computational analyses predicted that T201S was possibly deleterious, molecular strain typing, prion protein structural considerations, and calculations leveraging large-scale population data (gnomAD) indicate that T201S is at best either of low penetrance or nonpathogenic. Thus, we illustrate the utility of harnessing multiple lines of prion disease-specific evidence in the evaluation of the T201S variant, which may be similarly applied to assess other novel variants in PRNP

The clinical, neuroanatomical, and neuropathologic phenotype of TBK1-associated frontotemporal dementia: A longitudinal case report

Introduction: Mutations in the TANK-binding kinase 1 (TBK1) gene have recently been shown to cause frontotemporal dementia (FTD). However, the phenotype of TBK1-associated FTD is currently unclear. / Methods: We performed a single case longitudinal study of a patient who was subsequently found to have a novel A705fs mutation in the TBK1 gene. He was assessed annually for more than a 7-year period with a series of clinical, cognitive, and magnetic resonance imaging assessments. His brain underwent pathological examination at postmortem. / Results: The patient presented at the age of 64 years with an 18-month history of personality change including increased rigidity and obsessiveness, apathy, loss of empathy, and development of a sweet tooth. His mother had developed progressive behavioral and cognitive impairment from the age of 57 years. Neuropsychometry revealed intact cognition at first assessment. Magnetic resonance imaging showed focal right temporal lobe atrophy. Over the next few years his behavioral problems progressed and he developed cognitive impairment, initially with anomia and prosopagnosia. Neurological examination remained normal throughout without any features of motor neurone disease. He died at the age of 72 years and postmortem showed TDP-43 type A pathology but with an unusual novel feature of numerous TDP-43–positive neuritic structures at the cerebral cortex/subcortical white matter junction. There was also associated argyrophilic grain disease not previously reported in other TBK1 mutation cases. / Discussion: TBK1-associated FTD can be associated with right temporal variant FTD with progressive behavioral change and relatively intact cognition initially. The case further highlights the benefits of next-generation sequencing technologies in the diagnosis of neurodegenerative disorders and the importance of detailed neuropathologic analysis