Differential impairment of cerebrospinal fluid synaptic biomarkers in the genetic forms of frontotemporal dementia
Authors: Sogorb-Esteve Aitana , Nilsson Johanna , Swift Imogen J. , Heller Carolin , Bocchetta Martina , Russell Lucy L. , Peakman Georgia , Convery Rhian S. , van Swieten John C. , Seelaar Harro , Borroni Barbara , Galimberti Daniela , Sanchez-Valle Raquel , Laforce Robert , Moreno Fermin , Synofzik Matthis , Graff Caroline , Masellis Mario , Tartaglia Maria Carmela , Rowe James B. , Vandenberghe Rik , Finger Elizabeth , Tagliavini Fabrizio , Santana Isabel , Butler Chris R. , Ducharme Simon , Gerhard Alexander , Danek Adrian , Levin Johannes , Otto Markus , Sorbi Sandro , Le Ber Isabelle , Pasquier Florence , Gobom Johan , Brinkmalm Ann , Blennow Kaj , Zetterberg Henrik , Rohrer Jonathan D. ,   on behalf of the GENetic FTD Initiative, Nelson Annabel , Bouzigues Arabella , Greaves Caroline V , Cash David , Thomas David L , Todd Emily , Benotmane Hanya , Nicholas Jennifer , Samra Kiran , Shafei Rachelle , Timberlake Carolyn , Cope Thomas , Rittman Timothy , Benussi Alberto , Premi Enrico , Gasparotti Roberto , Archetti Silvana , Gazzina Stefano , Cantoni Valentina , Arighi Andrea , Fenoglio Chiara , Scarpini Elio , Fumagalli Giorgio , Borracci Vittoria , Rossi Giacomina , Giaccone Giorgio , Di Fede Giuseppe , Caroppo Paola , Tiraboschi Pietro , Prioni Sara , Redaelli Veronica , Tang-Wai David , Rogaeva Ekaterina , Castelo-Branco Miguel , Freedman Morris , Keren Ron , Black Sandra , Mitchell Sara , Shoesmith Christen , Bartha Robart , Rademakers Rosa , Poos Jackie , Papma Janne M. , Giannini Lucia , van Minkelen Rick , Pijnenburg Yolande , Nacmias Benedetta , Ferrari Camilla , Polito Cristina , Lombardi Gemma , Bessi Valentina , Veldsman Michele , Andersson Christin , Thonberg Hakan , Öijerstedt Linn , Jelic Vesna , Thompson Paul , Langheinrich Tobias , Lladó Albert , Antonell Anna , Olives Jaume , Balasa Mircea , Bargalló Nuria , Borrego-Ecija Sergi , de Mendonça Alexandre , Verdelho Ana , Maruta Carolina , Ferreira Catarina B. , Miltenberger Gabriel , do Couto Frederico Simões , Gabilondo Alazne , Gorostidi Ana , Villanua Jorge , Cañada Marta , Tainta Mikel , Zulaica Miren , Barandiaran Myriam , Alves Patricia , Bender Benjamin , Wilke Carlo , Graf Lisa , Vogels Annick , Vandenbulcke Mathieu , Van Damme Philip , Bruffaerts Rose , Poesen Koen , Rosa-Neto Pedro , Gauthier Serge , Camuzat Agnès , Brice Alexis , Bertrand Anne , Funkiewiez Aurélie , Rinaldi Daisy , Saracino Dario , Colliot Olivier , Sayah Sabrina , Prix Catharina , Wlasich Elisabeth , Wagemann Olivia , Loosli Sandra , Schönecker Sonja , Hoegen Tobias , Lombardi Jolina , Anderl-Straub Sarah , Rollin Adeline , Kuchcinski Gregory , Bertoux Maxime , Lebouvier Thibaud , Deramecourt Vincent , Santiago Beatriz , Duro Diana , Leitão Maria João , Almeida Maria Rosario , Tábuas-Pereira Miguel , Afonso Sónia 
Published: August 2022

Abstract
Background
Approximately a third of frontotemporal dementia (FTD) is genetic with mutations in three genes accounting for most of the inheritance: C9orf72, GRN, and MAPT. Impaired synaptic health is a common mechanism in all three genetic variants, so developing fluid biomarkers of this process could be useful as a readout of cellular dysfunction within therapeutic trials.

Methods
A total of 193 cerebrospinal fluid (CSF) samples from the GENetic FTD Initiative including 77 presymptomatic (31 C9orf72, 23 GRN, 23 MAPT) and 55 symptomatic (26 C9orf72, 17 GRN, 12 MAPT) mutation carriers as well as 61 mutation-negative controls were measured using a microflow LC PRM-MS set-up targeting 15 synaptic proteins: AP-2 complex subunit beta, complexin-2, beta-synuclein, gamma-synuclein, 14–3-3 proteins (eta, epsilon, zeta/delta), neurogranin, Rab GDP dissociation inhibitor alpha (Rab GDI alpha), syntaxin-1B, syntaxin-7, phosphatidylethanolamine-binding protein 1 (PEBP-1), neuronal pentraxin receptor (NPTXR), neuronal pentraxin 1 (NPTX1), and neuronal pentraxin 2 (NPTX2). Mutation carrier groups were compared to each other and to controls using a bootstrapped linear regression model, adjusting for age and sex.

Results
CSF levels of eight proteins were increased only in symptomatic MAPT mutation carriers (compared with controls) and not in symptomatic C9orf72 or GRN mutation carriers: beta-synuclein, gamma-synuclein, 14–3-3-eta, neurogranin, Rab GDI alpha, syntaxin-1B, syntaxin-7, and PEBP-1, with three other proteins increased in MAPT mutation carriers compared with the other genetic groups (AP-2 complex subunit beta, complexin-2, and 14–3-3 zeta/delta). In contrast, CSF NPTX1 and NPTX2 levels were affected in all three genetic groups (decreased compared with controls), with NPTXR concentrations being affected in C9orf72 and GRN mutation carriers only (decreased compared with controls). No changes were seen in the CSF levels of these proteins in presymptomatic mutation carriers. Concentrations of the neuronal pentraxins were correlated with brain volumes in the presymptomatic period for the C9orf72 and GRN groups, suggesting that they become abnormal in proximity to symptom onset.

Conclusions
Differential synaptic impairment is seen in the genetic forms of FTD, with abnormalities in multiple measures in those with MAPT mutations, but only changes in neuronal pentraxins within the GRN and C9orf72 mutation groups. Such markers may be useful in future trials as measures of synaptic dysfunction, but further work is needed to understand how these markers change throughout the course of the disease.