Functional Activity of TDP 43: A Direct Biomarker for ALS
Sonkar, K. S.; D'Ancona, V. L.; Cramp, J.; Shilling, H.; Giles, E.; Howell Bray, T.; Fillingham, B.; Cudkowicz, M. E.; Nath, A.; Rothstein, J. D.; Bowser, R.; Borroni, B.; Padovani, A.; Berry, J. D.; Vakili, G. S.; Buratti, E.; Thrippleton, I. P.
Show abstract
TDP-43 dysfunction is a defining feature of amyotrophic lateral sclerosis (ALS), yet no biofluid biomarker directly measures its functional activity. We developed a serum-based homogeneous time-resolved FRET (hTR-FRET) assay that quantifies TDP-43 RNA-binding activity using synthetic UU rich RNA probes. We analyzed 1,080 serum samples from controls, sporadic ALS, and genetic subgroups (C9orf72, SOD1) across multiple biorepositories. Cross-sectionally, TDP-43 ligation activity was elevated in ALS (mean 390 a.u.) versus controls (304 a.u.), yielding AUC = 0.79. Genotype means were 392 a.u. (sporadic), 382 a.u. (C9orf72), and 323 a.u. (SOD1); with a 366 a.u threshold achieved 95% specificity against controls. Longitudinally, Target ALS showed a modest but significant inverse correlation between TDP-43 activity and ALSFRS-R, while other cohorts exhibited similar non-significant trends. Elevated signal likely reflects increased extracellular, probe-competent TDP-43 species. This assay provides direct functional measurement of disease-relevant TDP-43 biology, supporting applications in diagnostic discrimination, genotype stratification, and progression monitoring in prospective studies.
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