Clinical phenotypes and genetic biomarkers of FTLD

Understanding neurobehavioral genetics of zebrafish

Due to its fully sequenced genome, high genetic homology to humans, external fertilization, fast development, transparency of embryos, low cost and active reproduction, the zebrafish (Danio rerio) has become a novel promising model organism in biomedicine. Zebrafish are a useful tool in genetic and neuroscience research, including linking various genetic mutations to brain mechanisms using forward and reverse genetics. These approaches have produced novel models of rare genetic CNS disorders and common brain illnesses, such as addiction, aggression, anxiety and depression. Genetically modified zebrafish also foster neuroanatomical studies, manipulating neural circuits and linking them to different behaviors. Here, we discuss recent advances in neurogenetics of zebrafish, and evaluate their unique strengths, inherent limitations and the rapidly growing potential for elucidating the conserved roles of genes in neuropsychiatric disorders.

Multimodal MRI of grey matter, white matter, and functional connectivity in cognitively healthy mutation carriers at risk for frontotemporal dementia and Alzheimer's disease

BACKGROUND

Frontotemporal dementia (FTD) and Alzheimer's disease (AD) are associated with divergent differences in grey matter volume, white matter diffusion, and functional connectivity. However, it is unknown at what disease stage these differences emerge. Here, we investigate whether divergent differences in grey matter volume, white matter diffusion, and functional connectivity are already apparent between cognitively healthy carriers of pathogenic FTD mutations, and cognitively healthy carriers at increased AD risk.

METHODS

We acquired multimodal magnetic resonance imaging (MRI) brain scans in cognitively healthy subjects with (n=39) and without (n=36) microtubule-associated protein Tau (MAPT) or progranulin (GRN) mutations, and with (n=37) and without (n=38) apolipoprotein E ε4 (APOE4) allele. We evaluated grey matter volume using voxel-based morphometry, white matter diffusion using tract-based spatial statistics (TBSS), and region-to-network functional connectivity using dual regression in the default mode network and salience network. We tested for differences between the respective carriers and controls, as well as for divergence of those differences. For the divergence contrast, we additionally performed region-of-interest TBSS analyses in known areas of white matter diffusion differences between FTD and AD (i.e., uncinate fasciculus, forceps minor, and anterior thalamic radiation).

RESULTS

MAPT/GRN carriers did not differ from controls in any modality. APOE4 carriers had lower fractional anisotropy than controls in the callosal splenium and right inferior fronto-occipital fasciculus, but did not show grey matter volume or functional connectivity differences. We found no divergent differences between both carrier-control contrasts in any modality, even in region-of-interest analyses.

CONCLUSIONS

Concluding, we could not find differences suggestive of divergent pathways of underlying FTD and AD pathology in asymptomatic risk mutation carriers. Future studies should focus on asymptomatic mutation carriers that are closer to symptom onset to capture the first specific signs that may differentiate between FTD and AD.

A new MAPT deletion in a case of speech apraxia leading to corticobasal syndrome

Speech apraxia is a disorder of speech motor planning/programming leading to slow rate, articulatory distortion, and distorted sound substitutions. We describe the clinical profile evolution of a patient presenting with slowly progressive isolated speech apraxia that eventually led to the diagnosis of corticobasal syndrome (CBS), supporting the evidence that this rare speech disorder can be the first presentation of CBS. Moreover, we found a novel variant in MAPT gene, which is hypothesized to be disease-causing mutation. These results underscore the importance of genetic analysis - particularly in selected atypical cases - for in vivo understanding of possible pathophysiological disease process.

Clinical Trials in a Dish: The Potential of Pluripotent Stem Cells to Develop Therapies for Neurodegenerative Diseases

Neurodegenerative diseases are a leading cause of death. No disease-modifying therapies are available, and preclinical animal model data have routinely failed to translate into success for therapeutics. Induced pluripotent stem cell (iPSC) biology holds great promise for human in vitro disease modeling because these cells can give rise to any cell in the human brain and display phenotypes specific to neurodegenerative diseases previously identified in postmortem and clinical samples. Here, we explore the potential and caveats of iPSC technology as a platform for drug development and screening, and the future potential to use large cohorts of disease-bearing iPSCs to perform clinical trials in a dish.

Classification of primary progressive aphasia: Do unsupervised data mining methods support a logopenic variant?

Our objective was to test whether data mining techniques, through an unsupervised learning approach, support the three-group diagnostic model of primary progressive aphasia (PPA) versus the existence of two main/classic groups. A series of 155 PPA patients observed in a clinical setting and subjected to at least one neuropsychological/language assessment was studied. Several demographic, clinical and neuropsychological attributes, grouped in distinct sets, were introduced in unsupervised learning methods (Expectation Maximization, K-Means, X-Means, Hierarchical Clustering and Consensus Clustering). Results demonstrated that unsupervised learning methods revealed two main groups consistently obtained throughout all the analyses (with different algorithms and different set of attributes). One group included most of the agrammatic/non-fluent and some logopenic cases while the other was mainly composed of semantic and logopenic cases. Clustering the patients in a larger number of groups (k > 2) revealed some clusters composed mostly of non-fluent or of semantic cases. However, we could not evidence any group chiefly composed of logopenic cases. In conclusion, unsupervised data mining approaches do not support a clear distinction of logopenic PPA as a separate variant.

Progranulin in neurodegenerative disease

Loss-of-function mutations in the progranulin gene are a common cause of familial frontotemporal dementia (FTD). The purpose of this review is to summarize the role of progranulin in health and disease, because the field is now poised to begin examining therapeutics that alter endogenous progranulin levels. We first review the clinical and neuropathological phenotype of FTD patients carrying mutations in the progranulin gene, which suggests that progranulin-mediated neurodegeneration is multifactorial and influenced by other genetic and/or environmental factors. We then examine evidence for the role of progranulin in the brain with a focus on mouse model systems. A better understanding of the complexity of progranulin biology in the brain will help guide the development of progranulin-modulating therapies for neurodegenerative disease.

Genomic editing opens new avenues for zebrafish as a model for neurodegeneration

Zebrafish has become a popular model organism to study human diseases. We will highlight the advantages and limitations of zebrafish as a model organism to study neurodegenerative diseases and introduce zinc finger nucleases, transcription activator-like effector nucleases, and the recently established clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated system for genome editing. The efficiency of the novel genome editing tools now greatly facilitates knock-out and, importantly, also makes knock-in approaches feasible in zebrafish. Genome editing in zebrafish avoids unspecific phenotypes caused by off-target effects and toxicity as frequently seen in conventional knock-down approaches.

Autosomal dominant frontotemporal lobar degeneration due to the C9ORF72 hexanucleotide repeat expansion: late-onset psychotic clinical presentation

BACKGROUND

A hexanucleotide repeat expansion in the first intron of C9ORF72 has been shown to be responsible for a high number of familial cases of amyotrophic lateral sclerosis or frontotemporal lobar degeneration (FTLD). Atypical presentations have been described, particularly psychosis.

METHODS

We determined the frequency of the hexanucleotide repeat expansions in a population of 651 FTLD patients and compared the clinical characteristics of carriers and noncarriers. In addition, we genotyped 21 patients with corticobasal syndrome, 31 patients with progressive supranuclear palsy, and 222 control subjects.

RESULTS

The pathogenic repeat expansion was detected in 39 (6%) patients with FTLD (17 male and 22 female subjects); however, it was not detected in any corticobasal syndrome and progressive supranuclear palsy patients or controls. Twenty-four of 39 carriers had positive family history for dementia and/or amyotrophic lateral sclerosis (61.5%), whereas only 145 of 612 noncarriers had positive family history (23.7%; p<.000001). Clinical phenotypes of carriers included 29 patients with the behavioral variant frontotemporal dementia (bvFTD; 5.2% of all bvFTD cases), 8 with bvFTD/motor neuron disease (32% bvFTD/motor neuron disease cases), 2 with semantic dementia (5.9% of patients with semantic dementia), and none with progressive nonfluent aphasia. The presentation with late-onset psychosis (median age = 63 years) was more frequent in carriers than noncarriers (10/33 vs. 3/37, p = .029), as well as the presence of cognitive impairment at onset (15/33 vs. 5/37; p = .0039).

CONCLUSIONS

The repeat expansion in C9ORF72 is a common cause of FTLD and often presents with late-onset psychosis or memory impairment.

Neuropathology of frontotemporal lobar degeneration: a review

Frontotemporal lobar degeneration (FTLD) is the second most common cause of presenile dementia. Three main clinical variants are widely recognized within the FTLD spectrum: the behavioural variant of frontotemporal dementia (bvFTD), semantic dementia (SD) and progressive non-fluent aphasia (PNFA). FTLD represents a highly heterogeneous group of neurodegenerative disorders which are best classified according to the main protein component of pathological neuronal and glial inclusions. The most common pathological class of FTLD is associated with the TDP-43 protein (FTLD-TDP), while FTLD-Tau is considered slightly less common while the FTLD-FUS (Fused in sarcoma protein) pathology is rare. In this review, these three major pathological types of FTLD are discussed.

Pathogenesis and disease-modifying therapy in Alzheimer's disease: the flat line of progress

The lack of progress in the development of disease-modifying therapy in Alzheimer's disease (AD) was highlighted recently by the cessation of a phase 3 clinical trial studying the effects of bapineuzumab on mild to moderate disease. No treatment benefit was apparent, whereas several serious side effects occurred more commonly in the treatment group compared to placebo. This is the latest failure in a now long list of trials targeting lesional proteins believed to be fundamental drivers of the disease process. As the focus of the trial is directly tied to ostensible disease pathogenesis, objectivity compels us yet again to re-examine the amyloid cascade hypothesis as even a marginally significant pathogenic mediator of disease and to perhaps revert back to traditional science where repeated negative data leads one to consider other ideas. In the case of AD, amyloid-β metabolism and tau phosphorylation have been exhaustively studied, both to no avail. Oxidative stress has similarly been examined in detail by multiple mechanisms and targeted for treatment with a similar result. An appeal to the scientific community may be made to consider lesions in a different light. Have we been seduced by so-called hallmark lesions into believing that they are responsible for disease when in fact the reverse is true, and will we genuinely consider a systems biology approach to AD or instead continue on the path of the lesion, which has so far followed a flat line of progress?