Reduced serum levels of pro-inflammatory chemokines in fragile X syndrome
Authors: Emanuela Martinuzzi
Anke Van Dijck
R Frank Kooy
Cyprien Gilet
Susana Barbosa
Olfa Khalfallah
Ellen Elinck
Laetitia Davidovic
Nicolas Glaichenhaus
Patricia Bermudez-Martin
Journal: BMC Neurology (2020)
Discipline: NEUROSCIENCE & BEHAVIOR
Keywords: Autism spectrum disorders; Biomarkers; Chemokines; Clustering; Cytokines
Affiliations: Department of Medical Genetics, University and University Hospital of Antwerp, Edegem, Belgium., Université Côte d'Azur, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France., Université Côte d'Azur, CNRS, Laboratoire Informatique Signaux et Systèmes de Sophia Antipolis, Valbonne, France., Université Côte d'Azur, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France. .

Abstract:  Background: Fragile X syndrome (FXS) is the most frequent cause of inherited intellectual disability and the most commonly identified monogenic cause of autism. Recent studies have shown that long-term pathological consequences of FXS are not solely confined to the central nervous system (CNS) but rather extend to other physiological dysfunctions in peripheral organs. To gain insights into possible immune dysfunctions in FXS, we profiled a large panel of immune-related biomarkers in the serum of FXS patients and healthy controls. Methods: We have used a sensitive and robust Electro Chemi Luminescence (ECL)-based immunoassay to measure the levels of 52 cytokines in the serum of n = 25 FXS patients and n = 29 healthy controls. We then used univariate statistics and multivariate analysis, as well as an advanced unsupervised clustering method, to identify combinations of immune-related biomarkers that could discriminate FXS patients from healthy individuals. Results: While the majority of the tested cytokines were present at similar levels in FXS patients and healthy individuals, nine chemokines, CCL2, CCL3, CCL4, CCL11, CCL13, CCL17, CCL22, CCL26 and CXCL10, were present at much lower levels in FXS patients. Using robust regression, we show that six of these biomarkers (CCL2, CCL3, CCL11, CCL22, CCL26 and CXCL10) were negatively associated with FXS diagnosis. Finally, applying the K-sparse unsupervised clustering method to the biomarker dataset allowed for the identification of two subsets of individuals, which essentially matched the FXS and healthy control categories. Conclusions: Our data show that FXS patients exhibit reduced serum levels of several chemokines and may therefore exhibit impaired immune responses. The present study also highlights the power of unsupervised clustering methods to identify combinations of biomarkers for diagnosis and prognosis in medicine. 

Retracted: No

PubPeer comments:
 In this study feeding times were not taken into consideration in the control and FXS cohorts. Feeding is known to significantly affect circulating cytokine levels (see for example *Nutrition J.* 10: 115, 2011). So results are of dubious significance in relationship to the FXS phenotype. , 
 In this study, there was a significantly enriched proportion of control subjects who were sampled before 8 am compared to patients with FXS (Z-score, p 0.05). This may have an important impact on measured cytokine serum levels, which display a circadian pattern (see for example *Sleep Sci. Pract.* 1: 18, 2017). , 
 One of the first molecular determinants defined in Fragile X cells is the reduced level of cAMP (Choi et al., Front Behav Neurosci. 2016 ; Kelley DJ, et al. Neurosci Biobehav Rev. 2008 ; Berry-Kravis E, et al. Pediatr Res. 1995 ). A low level of cAMP is known to be associated with inflammation. Indeed, drugs that elevate intracellular cAMP levels reduce the production of pro-inflammatory mediators and increase the production of anti-inflammatory factors in numerous immune cells (Raker et al., Fron Immunol, 2016) How do the authors explain that their results are in contradiction with the literature concerning cAMP in Fragile X Syndrome ? ,