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. 2021 May 18;7(3):e596.
doi: 10.1212/NXG.0000000000000596. eCollection 2021 Jun.

Novel TUBA4A Variant Associated With Familial Frontotemporal Dementia

Merel O Mol  1 , Tsz H Wong  1 , Shamiram Melhem  1 , Sreya Basu  1 , Riccardo Viscusi  1 , Niels Galjart  1 , Annemieke J M Rozemuller  1 , Claudia Fallini  1 , John E Landers  1 , Laura Donker Kaat  1 , Harro Seelaar  1 , Jeroen G J van Rooij  1 , John C van Swieten  1
Affiliations

Novel TUBA4A Variant Associated With Familial Frontotemporal Dementia

Merel O Mol et al. Neurol Genet. .

Abstract

Objective: Despite the strong genetic component of frontotemporal dementia (FTD), a substantial proportion of patients remain genetically unresolved. We performed an in-depth study of a family with an autosomal dominant form of FTD to investigate the underlying genetic cause.

Methods: Following clinical and pathologic characterization of the family, genetic studies included haplotype sharing analysis and exome sequencing. Subsequently, we performed immunohistochemistry, immunoblotting, and a microtubule repolymerization assay to investigate the potential impact of the candidate variant in tubulin alpha 4a (TUBA4A).

Results: The clinical presentation in this family is heterogeneous, including behavioral changes, parkinsonian features, and uncharacterized dementia. Neuropathologic examination of 2 patients revealed TAR DNA binding protein 43 (TDP-43) pathology with abundant dystrophic neurites and neuronal intranuclear inclusions, consistent with frontotemporal lobar degeneration-TDP type A. We identified a likely pathogenic variant in TUBA4A segregating with disease. TUBA4A encodes for α-tubulin, which is a major component of the microtubule network. Variants in TUBA4A have been suggested as a rare genetic cause of amyotrophic lateral sclerosis (ALS) and have sporadically been reported in patients with FTD without supporting genetic segregation. A decreased trend of TUBA4A protein abundance was observed in patients compared with controls, and a microtubule repolymerization assay demonstrated disrupted α-tubulin function. As opposed to variants found in ALS, TUBA4A variants associated with FTD appear more localized to the N-terminus, indicating different pathogenic mechanisms.

Conclusions: Our findings support the role of TUBA4A variants as rare genetic cause of familial FTD.

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Figures

Figure 1
Figure 1. Pedigree of the Family
Filled black symbols represent affected patients. Deceased patients are marked by a diagonal line. Numbers within the symbols represent additional unaffected relatives. Numbers in parentheses indicate age at death or age at last evaluation. Brain autopsy was performed in the 2 patients marked by asterisk. Individual II:9 was considered a patient with sporadic late-onset AD and was not included in the initial genetic analyses. Four patients (blue marks) were included in the haplotype sharing analysis. Exome sequencing was performed including these 4 patients and 2 relatives (red marks). Two additional relatives were tested for the TUBA4A R105C variant by Sanger sequencing. Men and woman were affected equally (sex masked for anonymity). TUBA4A R105C status: +/− = carrier, −/− = noncarrier; upper row whole-exome sequencing (WES); lower row Sanger sequencing. Patient III:1 was not tested by Sanger due to lack of DNA. AD = Alzheimer disease; bvFTD = behavioral variant of frontotemporal dementia; na = not available; PD = Parkinson disease; UD = unspecified dementia.
Figure 2
Figure 2. Immunohistochemistry of Patients III:6 and II:8 Confirming FTLD-TDP Pathology
The pathologic subtype of both patients resembles TDP type A considering the short and thick dystrophic neurites (DN), compact neuronal cytoplasmic inclusions (NCIs), and lentiform neuronal intranuclear inclusions (NIIs) mostly in the superficial layers of the cortex. The deeper layers were also affected, but to lesser extent. (A) Images of P62 staining (including 3 insets of a variety of neuronal inclusions) and (B) pTDP staining in patient III:6 show the DN, NCI, and NII in the second layer of temporal cortex. Staining with pTDP of patient II:8 revealed similar findings, with inclusions in (C) the dentate gyrus of hippocampus, and (D) second layer of temporal cortex (including 3 insets of neuronal inclusions). Scale bar: 20 μm. FTLD-TDP = frontotemporal lobar degeneration with TDP pathology.
Figure 3
Figure 3. Immunoblotting Showing a Decreased Trend of TUBA4A Protein Abundance in Patients
(A) Protein was extracted for immunoblotting from temporal cortex tissues of 2 patients (III:6 and II:8), 2 patients with FTLD-TDP type A caused by a pathogenic GRN variant (GRN), 2 patients with Alzheimer disease (AD), and 5 NDCs. Blots were performed in technical duplicates and normalized to the housekeeping gene GAPDH. Immunoblots are shown of the first isolation, with technical duplicates of TUBA4A. (B) The relative TUBA4A protein abundance of biological triplicates was normalized to the mean abundance of the 5 NDCs. A visible trend is observed of decreased TUBA4A protein levels in patients compared with NDCs and disease controls, although a high degree of variation exits among NDCs. III:6 vs NDC, p = 0.005; III:6 vs AD, p < 0.001; III:6 vs GRN, p = 0.002; II:8 vs NDC, p = 0.03; II:8 vs AD, p = 0.002; II:8 vs GRN, p = 0.20 (unpaired t tests). FTLD-TDP = frontotemporal lobar degeneration with TDP pathology; GAPDH = glyceraldehyde-3-phosphate dehydrogenase.
Figure 4
Figure 4. Microtubule Repolymerization Assay Showing Cells After 10 Minutes of Nocodazole Washout
The arrows indicate neuronal inclusions and dystrophic neurites immunoreactive to P62 (A) and pTDP-43 (B). (A) COS1 cells were transfected either with hemagglutinin (HA)-tagged wild-type (WT) tubulin, R105C, or R320C mutant constructs and exposed to high dose of nocodazole to completely depolymerize all microtubules. We studied the repolymerization potential of microtubules at 0, 5, 10, and 30 minutes following nocodazole washout. The cells were stained to visualize endogenous tubulin with anti-β-tubulin (green) and the constructs using anti-HA antibody (red). Magnified insets show the cellular area where the centrosome is located, as indicated by the arrows. At the 0 minute time point, the centrosomes are absent (figure e-3, links.lww.com/NXG/A426), yet each time point thereafter shows an increase of cells with visible centrosome and newly formed microtubules. The images show examples of cells fixed after 10 minutes. (B.a and B.b) The graphs below depict the quantified fraction of cells with recovered microtubules at the different time points. Neither of the 2 mutant tubulins significantly affect recovery of the microtubule network (anti–β-tubulin; B.a), but both mutants do not incorporate efficiently into the newly formed microtubule network (anti-HA; B.b). Anti-HA at 10-minute recovery: WT vs R105C, p < 0.05; WT vs R320C, p < 0.001. Anti-HA at 30 minute recovery: WT vs R105C, p < 0.01; WT vs R320C, p < 0.01 (unpaired t tests). Scale bar: 10 μm.
Figure 5
Figure 5. Schematic Representation of the TUBA4A Protein Structure With Identified and Previously Reported Variants
The genetic variants in TUBA4A are organized according to clinical phenotype, revealing that all variants associated with FTD or ALS-FTD are located in the GTPase domain. The majority of the variants found in ALS patients are localized in exon 4 in the C-terminal domain. For 1 variant (V7I), the phenotype was not described. The R015C variant identified in this study (red box) is the only variant located in exon 3. Underlined variants: positive family history for dementia; bold variants: functional assay supporting variant. ALS = amyotrophic lateral sclerosis; FTD = frontotemporal dementia. Additional details for each variant can be found in table e-2 (links.lww.com/NXG/A426).
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References

    1. Olney NT, Spina S, Miller BL. Frontotemporal dementia. Neurol Clin. 2017;35(2):339-374. - PMC - PubMed
    1. Beeldman E, Raaphorst J, Klein Twennaar M, de Visser M, Schmand BA, de Haan RJ. The cognitive profile of ALS: a systematic review and meta-analysis update. J Neurol Neurosurg Psychiatry. 2016;87(6):611-619. - PubMed
    1. Burrell JR, Halliday GM, Kril JJ, et al. . The frontotemporal dementia-motor neuron disease continuum. Lancet. 2016;388(10047):919-931. - PubMed
    1. Rohrer JD, Guerreiro R, Vandrovcova J, et al. . The heritability and genetics of frontotemporal lobar degeneration. Neurology. 2009;73(18):1451-1456. - PMC - PubMed
    1. Moore KM, Nicholas J, Grossman M, et al. . Age at symptom onset and death and disease duration in genetic frontotemporal dementia: an international retrospective cohort study. Lancet Neurol. 2020;19(2):145-156. - PMC - PubMed