TAF1 Transcripts and Neurofilament Light Chain as Biomarkers for X‐linked Dystonia‐Parkinsonism

Abstract

Background X‐linked dystonia‐parkinsonism is a rare neurological disease endemic to the Philippines. Dystonic symptoms appear in males at the mean age of 40 years and progress to parkinsonism with degenerative pathology in the striatum. A retrotransposon inserted in intron 32 of the TAF1 gene leads to alternative splicing in the region and a reduction of the full‐length mRNA transcript. Objectives The objective of this study was to discover cell‐based and biofluid‐based biomarkers for X‐linked dystonia‐parkinsonism. Methods RNA from patient‐derived neural progenitor cells and their secreted extracellular vesicles were used to screen for dysregulation of TAF1 expression. Droplet‐digital polymerase chain reaction was used to quantify the expression of TAF1 mRNA fragments 5′ and 3′ to the retrotransposon insertion and the disease‐specific splice variant TAF1‐32i in whole‐blood RNA. Plasma levels of neurofilament light chain were measured using single‐molecule array. Results In neural progenitor cells and their extracellular vesicles, we confirmed that the TAF1‐3′/5′ ratio was lower in patient samples, whereas TAF1‐32i expression is higher relative to controls. In whole‐blood RNA, both TAF1‐3′/5′ ratio and TAF1‐32i expression can differentiate patient (n = 44) from control samples (n = 18) with high accuracy. Neurofilament light chain plasma levels were significantly elevated in patients (n = 43) compared with both carriers (n = 16) and controls (n = 21), with area under the curve of 0.79. Conclusions TAF1 dysregulation in blood serves as a disease‐specific biomarker that could be used as a readout for monitoring therapies targeting TAF1 splicing. Neurofilament light chain could be used in monitoring neurodegeneration and disease progression in patients. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Variation in TAF1 expression in female carrier induced pluripotent stem cells and human brain ontogeny has implications for adult neostriatum vulnerability in X-linked Dystonia Parkinsonism

“…An extremely skewed (98%:2%) XCI was noted in only a single case with full XDP syndrome (Domingo et al, 2014), and X-chromosome monosomy (45,X/46,XX) was found in a subset of cells of another female patient with XDP(Westenberger et al, 2013). A recent study examining the peripheral blood of 17 carrier females (4 affected with parkinsonism and 13 non affected) (Al Ali et al, 2021), is also consistent with a mosaic XCI status being protective. Decreased full length TAF1 expression, as measured by the ratio of TAF1 3’/5’, is at an intermediate level for asymptomatic carriers such that XDP patients demonstrated the most reduction and asymptomatic female carriers demonstrated intermediate reduction compared to healthy controls.…”

“…Canonical TAF1 expression was decreased in various XDP samples, including fibroblast, RNA from blood and NSCs, compared to control samples (Al Ali et al, 2021; Aneichyk et al, 2018; Domingo et al, 2016; Ito et al, 2016). To quantify the 3’ region of canonical TAF1 expression in XDP female carrier-derived iPSCs, we performed RT-qPCR with primers targeting TAF1 exons 32 and 33 (Rakovic et al, 2018).…”

“…In contrast, female lines containing the active wild-type allele and silenced mutant allele had no detectable levels of TAF1-32i, a situation similar to control male iPSC lines and lines with a CRISPR-deleted SVA. A recent study demonstrated that TAF1-32i expression was elevated in XDP patients and female carriers compared to control samples but TAF1-32i expression levels did not distinguish carriers vs affected XDP patients (Al Ali et al, 2021). Our data suggest that the XDP haplotype is fully silenced by XCI and that TAF1-32i expression is a biomarker for XDP haplotype expression in female pluripotent stem cells.…”

“…XDP patient samples have decreased expression of the canonical full-length TAF1 ( cTAF1 ) transcript in dividing cells (Aneichyk et al, 2018; Rakovic et al, 2018), patient blood RNA (Al Ali et al, 2021), and a 2D cellular model of MSNs (Rakovic et al, 2018). The cTAF1 decreases are caused by the SVA, which induces alternative splicing and intron retention (Aneichyk et al, 2018).…”

Tissue-specific and repeat length-dependent somatic instability of the X-linked dystonia parkinsonism-associated CCCTCT repeat

“…Among the thirteen disease-specific variants is a ∼2.6 kb SINE-VNTR-Alu (SVA)-type retrotransposon [21] inserted in intron 32 of TAF1 [19]. XDP patient tissues and cell lines exhibit reduced TAF1 expression [19,20,22–25] as well as aberrant splicing that results in partial retention of intronic sequence proximal to the SVA insertion [20]. Reduced TAF1 expression, intron retention and aberrant splicing can be rescued by excision of the SVA [20,23], suggesting that SVA-mediated TAF1 transcriptional dysregulation may contribute to disease pathogenesis.…”