Freigang et al. Orphanet J Rare Dis (2021) 16:330 https://doi.org/10.1186/s13023-021-01961-8 RESEARCH Open Access Increased chitotriosidase 1 concentration following nusinersen treatment in spinal muscular atrophy Maren Freigang1†, Petra Steinacker2†, Claudia Diana Wurster2, Olivia Schreiber‑Katz3, Alma Osmanovic3, Susanne Petri3, Jan Christoph Koch4, Kevin Rostásy5, Björn Falkenburger1,6, Albert Christian Ludolph2,7, Markus Otto2, Andreas Hermann8,9† and René Günther1,6*† Abstract Background: Studies regarding the impact of (neuro)infammation and infammatory response following repeti‑ tive, intrathecally administered antisense oligonucleotides (ASO) in 5q‑associated spinal muscular atrophy (SMA) are sparse. Increased risk of hydrocephalus in untreated SMA patients and a marginal but signifcant increase of the serum/CSF albumin ratio (Qalb) with rare cases of communicating hydrocephalus during nusinersen treatment were reported, which confrms the unmet need of an infammatory biomarker in SMA. The aim of this study was to inves‑ tigate the (neuro)infammatory marker chitotriosidase 1 (CHIT1) in SMA patients before and following the treatment with the ASO nusinersen. Methods: In this prospective, multicenter observational study, we studied CSF CHIT1 concentrations in 58 adult and 21 pediatric patients with SMA type 1, 2 or 3 before treatment initiation in comparison to age‑ and sex‑matched controls and investigated its dynamics during nusinersen treatment. Concurrently, motor performance and disease severity were assessed. Results: CHIT1 concentrations were elevated in treatment‑naïve SMA patients as compared to controls, but less pro‑ nounced than described for other neurodegenerative diseases such as amyotrophic lateral sclerosis. CHIT1 concentra‑ tion did not correlate with disease severity and did not distinguish between clinical subtypes. CHIT1 concentration did show a signifcant increase during nusinersen treatment that was unrelated to the clinical response to nusinersen therapy. Conclusions: CHIT1 elevation in treatment‑naïve SMA patients indicates the involvement of (neuro)infammation in SMA. The lacking correlation of CHIT1 concentration with disease severity argues against its use as a marker of disease progression. The observed CHIT1 increase during nusinersen treatment may indicate an immune response‑like, of‑ target reaction. Since antisense oligonucleotides are an establishing approach in the treatment of neurodegenerative diseases, this observation needs to be further evaluated. Keywords: SMA, Chitotriosidase 1, Biomarker, Nusinersen, ASO Background *Correspondence: rene.guenther@uniklinikum‑dresden.de †Maren Freigang and Petra Steinacker shared frst authorship 5q-associated spinal muscular atrophy (SMA) is a rare †Andreas Hermann and René Günther shared last authorship lower motor neuron disease caused by mutations in the 1 Department of Neurology, Technische Universität Dresden, Dresden, survival motor neuron 1 (SMN1) gene resulting in def- Germany Full list of author information is available at the end of the article cient biosynthesis of SMN protein, death of lower motor © The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. 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ALS, CHIT1 levels were remarkably increased compared SMA is classifed into clinical subtypes according to the to both healthy and disease controls, and correlated best achieved motor milestone and age of onset [1]. In with disease progression and severity. CHIT1 stain- 2016, the United States Food and Drug Administration ing was restricted to specifc areas along the spinal tract (FDA) approved the antisense oligonucleotide (ASO) and was colocalized with markers of microglia and mac- nusinersen as the frst disease-modifying drug for SMA rophages indicating the presence of microgliosis, which for all patients, regardless of their age or disease stage, could not be detected in controls, AD or Creutzfeldt- based on exceptionally convincing study results [2, 3]. In Jakob disease. Additionally, CHIT1 levels were found to order to provide appropriate and standardized recom- be higher in TDP-43 associated FTLD with ALS pathol- mendations for choice of treatment and therapy (dis-) ogy compared to TDP-43 associated FTLD without continuation, conclusive biomarkers are urgently needed ALS pathology, which implies a relationship of CHIT1 [4–6]. increase with a specifc type of microgliosis/astroglio- Chitotriosidase 1 (CHIT1) is a human endochitinase, sis in corticoeferent pathways and/or association fbers that is expressed by polymorphonuclear neutrophils and [13, 20]. Further, CHIT1 levels were found to show the activated macrophages and is assumed to be involved most extensive increase between the late presymptomatic in innate immune system responses, e.g. after allergen and early symptomatic phases of disease, while patients challenge or pathogen exposure [7–10]. Consequently, after symptom onset present minimally increasing levels. a 24 base pair duplication in the CHIT1 gene (H allele) CHIT1 levels of asymptomatic gene carriers did not dif- with high prevalence in European populations is associ- fer from controls [15]. ated with a defciency in the activity of CHIT1 and is sus- In SMA, recent studies suggest that microglial activa- pected to result in a higher susceptibility to infection [11]. tion, driven by SMN protein defciency, contributes to CHIT1 hydrolyzes the β-(1-4)-linkage of N-acetyl-d-glu- the phenotype of SMA and even precedes motor neu- cosamine, which is present in chitin chains [7, 8, 10]. ron loss [30]. Motor neurons were colocalized with Although chitin is not expressed in human cells, CHIT1 an increased number of microglial cells in SMA mice levels are elevated in serum and cerebrospinal fuid (CSF) which indicates a certain degree of neuroinfammation in various diseases including Gaucher disease, idiopathic [31]. Increased risk of hydrocephalus in untreated SMA pulmonary fbrosis, sarcoidosis, chronic obstructive pul- patients and a marginal but signifcant increase of the monary disease and neurodegenerative/-infammatory serum/CSF albumin ratio (Qalb) with rare cases of com- diseases such as Alzheimer’s disease (AD), frontotempo- municating hydrocephalus during treatment with the ral dementia, multiple sclerosis (MS) and amyotrophic ASO nusinersen were reported [32–35]. lateral sclerosis (ALS) [7, 12–24]. In patients with MS, Te aim of this study was to evaluate CHIT as a marker the concentration of CHIT1 was elevated compared to of neuroinfammation in treatment-naïve patients with controls and was found to be associated with other well- SMA and to investigate its dynamics during nusinersen known MS-specifc fndings such as oligoclonal bands treatment. in CSF, elevated immunoglobulin G index, elevated CSF leukocyte count, and magnetic resonance imaging abnor- malities showing dissemination in space, thus assuming Methods to possess prognostic value [17]. In fact, CHIT1 activity Standard protocol approvals, registrations, and patient is already used for the evaluation of response to immu- consents nomodulatory treatment in MS as a marker of infam- 58 adult patients and 21 children with genetically con- matory activity [25, 26]. In the CSF of patients with AD, frmed 5q-associated SMA from 4 German motor neuron CHIT1 activity was shown to be increased [24]. CHIT1 disease specialist care centers (Departments of Neurol- activity was discussed to be either a DNA damage marker ogy in Dresden, Ulm, Hannover and Göttingen) and and / or a response to chitin-like polysaccharides, which 30 age- and sex-matched controls were prospectively were found to accumulate as part of amyloid deposits in included in this study between 2017 and 2020. Te local the brain of patients with AD, presumably as a conse- ethics committees of all participating sites approved the quence of impaired glucose metabolism [27, 28]. Patients study and all patients signed written informed consent. with neurodegenerative dementia revealed signifcantly Te demographic and clinical data of patients were increased CHIT1 levels, which illustrates neuroinfam- collected including age, gender, disease onset, baseline mation as a common pathophysiological mechanism. weight and height, clinical subtype, number of SMN2 However, because of overlapping levels of CHIT1 in copies if available and ambulatory status. Additionally, prion disease, AD and frontotemporal lobar degenera- the need