The chromosome 17q21.31 region, containing a 900 Kb inversion that defines H1 and H2 haplotypes, represents the strongest genetic risk locus in progressive supranuclear palsy (PSP). In addition to H1 and H2, various structural forms of 17q21.31, characterized by the copy number of α, β, and γ duplications, have been identified. However, the specific effect of each structural form on the risk of PSP has never been evaluated in a large cohort study.
Abstract Background Progressive supranuclear palsy (PSP) is a rare neurodegenerative disease characterized by the accumulation of aggregated tau proteins in astrocytes, neurons, and oligodendrocytes. Previous genome-wide association studies for PSP were based on genotype array, therefore, were inadequate for the analysis of rare variants as well as larger mutations, such as small insertions/deletions (indels) and structural variants (SVs). Method In this study, we performed whole genome sequencing (WGS) and conducted association analysis for single nucleotide variants (SNVs), indels, and SVs, in a cohort of 1,718 cases and 2,944 controls of European ancestry. Of the 1,718 PSP individuals, 1,441 were autopsy-confirmed and 277 were clinically diagnosed. Results Our analysis of common SNVs and indels confirmed known genetic loci at MAPT , MOBP , S TX6 , SLCO1A2 , DUSP10 , and SP1 , and further uncovered novel signals in APOE , FCHO1/MAP1S, KIF13A, TRIM24, TNXB, and ELOVL1 . Notably, in contrast to Alzheimer’s disease (AD), we observed the APOE ε2 allele to be the risk allele in PSP. Analysis of rare SNVs and indels identified significant association in ZNF592 and further gene network analysis identified a module of neuronal genes dysregulated in PSP. Moreover, seven common SVs associated with PSP were observed in the H1/H2 haplotype region (17q21.31) and other loci, including IGH , PCMT1 , CYP2A13 , and SMCP . In the H1/H2 haplotype region, there is a burden of rare deletions and duplications ( P = 6.73 × 10 –3 ) in PSP. Conclusions Through WGS, we significantly enhanced our understanding of the genetic basis of PSP, providing new targets for exploring disease mechanisms and therapeutic interventions.
Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are closely related disorders, linked pathologically and genetically by the TAR DNA-binding protein-43 (TDP-43). Pathogenic variants in TARDBP encoding for TDP-43 have been described less frequently in FTD than in ALS, and clinicopathological studies are scarce.1 We previously observed a high frequency of the I383V variant in TARDBP in a Dutch cohort of FTD patients.2 Here, we provide further evidence for the pathogenicity of this variant and present its clinicopathological characteristics.
We ascertained all FTD (n=13) and ALS patients (n=4) with the I383V variant (NM_007375.3: c.1147A>G, p.Ile383Val) in TARDBP from three university medical centres in the Netherlands (Amsterdam, Rotterdam and Utrecht), as identified by whole-exome or whole-genome sequencing in either clinical or research setting. Concurrent pathogenic variants in 20 other genes associated with ALS, FTD or other forms of dementia were excluded in all patients.
Brain imaging (CT or MRI) was available for all FTD patients. Quantitative assessment of volume loss across lobar brain regions was performed in those patients with T1-weighted MRI images of sufficient quality (n=5), and compared with a gender-matched/age-matched reference population.
Family histories were classified into adjusted Goldman categories, which were described previously.2 Additionally, we performed extensive genealogical research to investigate possible relatedness between the index patients.
Brain autopsy and routine immunohistochemistry was performed for two FTD patients by the Netherlands Brain Bank. One patient (4M) was reported previously as M008015-001.1 Detailed information on the genetic, neuroimaging, genealogical and pathological analyses can be found in the1.
### Supplementary data
[jnnp-2020-325150supp001.pdf]
### The variable clinical phenotype and reduced penetrance of the I383V variant
All 13 FTD patients with the I383V variant in TARDBP presented with a combination of behavioural changes and semantic deficits. The diagnoses of semantic variant of primary progressive aphasia (svPPA) are intriguing since this is usually considered a sporadic disorder. One patient (4M) showed additional motor …
Abstract Introduction Trials to test disease-modifying treatments for frontotemporal dementia are eagerly awaited and sensitive instruments to assess potential treatment effects are increasingly urgent, yet lacking thus far. We aimed to identify gene-specific instruments assessing clinical onset and disease progression by comparing cognitive functioning between bvFTD patients across genetic mutations. Methods We examined differences in 7 cognitive domains between bvFTD patients with GRN ( n = 20), MAPT ( n = 29) or C9orf72 ( n = 31) mutations, and non-carriers ( n = 24), and described longitudinal ( M = 22.6 months, SD = 16.6) data in a subsample ( n = 27). Results Patients showed overall cognitive impairment, except memory recall, working memory and visuoconstruction. GRN patients performed lower on executive function (mean difference − 2.1; 95%CI − 4.1 to − 0.5) compared to MAPT and lower on attention compared to MAPT (mean difference − 2.5; 95%CI − 4.7 to − 0.3) and C9orf72 (mean difference − 2.4; 95%CI − 4.5 to − 0.3). Only MAPT patients were impaired on delayed recall (mean difference − 1.4; 95%CI − 2.1 to − 0.7). GRN patients declined rapidly on attention and memory, MAPT declined in confrontation naming, whereas C9orf72 patients were globally impaired but remained relatively stable over time on all cognitive domains. Discussion This study shows gene-specific cognitive profiles in bvFTD, which underlines the value of neuropsychological tests as outcome measures in upcoming trials for genetic bvFTD.
We performed 4-year follow-up neuropsychological assessment to investigate cognitive decline and the prognostic abilities from presymptomatic to symptomatic familial frontotemporal dementia (FTD). Presymptomatic MAPT (n = 15) and GRN mutation carriers (n = 31), and healthy controls (n = 39) underwent neuropsychological assessment every 2 years. Eight mutation carriers (5 MAPT, 3 GRN) became symptomatic. We investigated cognitive decline with multilevel regression modeling; the prognostic performance was assessed with ROC analyses and stepwise logistic regression. MAPT converters declined on language, attention, executive function, social cognition, and memory, and GRN converters declined on attention and executive function (p < 0.05). Cognitive decline in ScreeLing phonology (p = 0.046) and letter fluency (p = 0.046) were predictive for conversion to non-fluent variant PPA, and decline on categorical fluency (p = 0.025) for an underlying MAPT mutation. Using longitudinal neuropsychological assessment, we detected a mutation-specific pattern of cognitive decline, potentially suggesting prognostic value of neuropsychological trajectories in conversion to symptomatic FTD.
The aetiology of late-onset neurodegenerative diseases is largely unknown. Here we investigated whether de novo somatic variants for semantic dementia can be detected, thereby arguing for a more general role of somatic variants in neurodegenerative disease. Semantic dementia is characterized by a non-familial occurrence, early onset (<65 years), focal temporal atrophy and TDP-43 pathology. To test whether somatic variants in neural progenitor cells during brain development might lead to semantic dementia, we compared deep exome sequencing data of DNA derived from brain and blood of 16 semantic dementia cases. Somatic variants observed in brain tissue and absent in blood were validated using amplicon sequencing and digital PCR. We identified two variants in exon one of the TARDBP gene (L41F and R42H) at low level (1-3%) in cortical regions and in dentate gyrus in two semantic dementia brains, respectively. The pathogenicity of both variants is supported by demonstrating impaired splicing regulation of TDP-43 and by altered subcellular localization of the mutant TDP-43 protein. These findings indicate that somatic variants may cause semantic dementia as a non-hereditary neurodegenerative disease, which might be exemplary for other late-onset neurodegenerative disorders.
Progressive supranuclear palsy is a neurodegenerative disorder accompanied by parkinsonism, disturbances of eye movements, pseudobulbar palsy and often cognitive decline. Onset of disease is usually between 50-70 years of age and mean survival is 5-8 years. The prevalence of PSP has been estimated at around 5 per 100,000, although exact figures for the population of the Netherlands are not yet available. International consensus criteria differentiate between possible, probable and definite PSP; the latter requiring neuropathological confirmation. An extensive differential diagnosis may be made early in the course of the disease, but at a later stage development of the characteristic symptoms will make diagnosis easier. Imaging techniques can lend support to the clinical diagnosis to a limited extent, although they lack sufficient specificity to confirm it. PSP is a 'tauopathy' characterized by aggregates of abnormal tau protein in the basal ganglia and brainstem. Some mutations in the tau gene can cause a clinical and pathological picture similar to that of PSP, although most patients with sporadic and familial PSP do not have tau mutations. Various studies have found a strong association between PSP and a specific tau haplotype (H1 haplotype), but its role in the pathophysiological mechanism of PSP is still unclear and needs further research.
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