Detection of TDP-43 seeds in CSF of presymptomatic and symptomatic genetic FTD/ALS

Introduction: Seed amplification assays (SAAs) have shown promising results in detecting misfolded transactive response (TAR) DNA-binding protein 43 (TDP-43) in cerebrospinal fluid (CSF) of genetic frontotemporal dementia (FTD). To date, the use of SAA has yet to be evaluated in presymptomatic individuals. Methods: Thirty patients carrying GRN or C9orf72 mutations, 2 microtubule-associated protein tau (MAPT) carriers, 14 presymptomatic subjects, and 27 controls underwent CSF collection. We used SAA for detecting misfolded TDP-43 (TDP-43_SAA) and single molecule array (SIMOA) technology for neurofilament light chain (NfL) dosage. Results: TDP-43 seeding activity was detected in 67% of TDP-43-linked symptomatic patients, with a specificity of 93%. Almost half of presymptomatic subjects tested positive, mostly GRN carriers. Interestingly, among TDP-43_SAA positive presymptomatic individuals, two GRN carriers underwent phenoconversion. Discussion: TDP-43_SAA can also detect misfolded TDP-43 in the CSF of presymptomatic individuals. A possible link exists between positive TDP-43_SAA and conversion to the symptomatic phase. Highlights: Seed amplification assay of transactive response (TAR) DNA-binding protein 43 (TDP-43_SAA) can detect misfolded TDP-43 in the cerebrospinal fluid (CSF) of patients with genetic frontotemporal dementia (FTD), linked to GRN and C9orf72 mutations. TDP-43_SAA can detect misfolded TDP-43 also in the CSF of presymptomatic individuals. In both groups, most TDP-43_SAA positive cases were carriers of GRN mutation. Two GRN carriers that resulted TDP-43_SAA positive converted to the symptomatic phase of the disease.