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

Abstract

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.

Keywords: CSF; SAA; TDP‐43; amyotrophic lateral sclerosis; frontotemporal dementia; seed amplification assays.

FIGURE 1

TDP‐43_SAA analyses of CSF from genetic C9orf72 and GRN FTD and FTD‐ALS patients and presymptomatic carriers. Kinetic curves of TDP‐43 seeding activity in CSF from subjects with (A) C 9orf72 mutation, (B) GRN mutation, (C) presymptomatic carriers, and (D) controls (CTRLs + MAPT carriers). (A, B) The kinetic curves are indicated by purple lines for positive CSF from FTD/FTD‐ALS, ALS, and ALS‐FTD patients. (C) Presymptomatic carriers are divided into two groups, depending on the mutation. The green lines indicate C 9orf72 carriers, and the orange lines GRN carriers. All the samples that tested negative are indicated in gray. (D) The two positive controls are indicated in black, whereas all the samples that resulted negative are indicated in gray. The dotted lines indicate the fluorescence (AU) and time (h) thresholds. ALS, amyotrophic lateral sclerosis; CSF, cerebrospinal fluid; FTD, frontotemporal dementia; MAPT, microtubule‐associated protein tau; SAA, seed amplification assay; TDP‐43, transactive response (TAR) DNA‐binding protein 43.

FIGURE 2

CSF NfL levels by SIMOA in our study population. (A) Statistically significant increase in NfL levels was observed in patients compared to CTRLs and presymptomatic carriers (Pre‐sym) (Kruskal–Wallis test **** p < 0.0001). CSF NfL levels and SAA_ TDP‐43 in our study population. (B) NfL levels did not significantly differ between SAA+ and SAA‐ patients (Mann–Whitney test p = 0,8889). (C) SAA+ presymptomatic carriers (Presym_SAA+) presented higher NfL levels compared with SAA‐ presymptomatic carriers (Presym_SAA‐) (Mann–Whitney test *p = 0,0426), however the difference was no longer significant after adjusting for age (p = 0,097); red arrows show the two GRN carriers who underwent phenoconversion. CSF, cerebrospinal fluid; CTRL, control; NfL, neurofilament light chain; SAA, seed amplification assay; SIMOA, single molecule array.