Int J Rheum Dis. 2019;00:1–6. wileyonlinelibrary.com/journal/apl | 1 © 2019 Asia Pacific League of Associations for Rheumatology and John Wiley & Sons Australia, Ltd 1 | INTRODUCTION Human α‐fucosidase (EC 3.2.1.51) is a glycosidase able to hydrolyze O‐ and S‐glycosyl compounds, which has received major attention in recent years as a serological marker in some forms of cancer such as hepatocellular carcinoma. 1,2 The enzyme is particularly important in a rare form of pathology, known as fucosidosis, which is a severe glycoprotein lysosomal storage disorder, included in the group of oligosaccharides or glycoproteins. 3,4 Clinical hallmarks of fucosidosis include progressive psychomotor retardation, facial dysmorphism, deafness, angiokeratoma, neurologic signs, moderate hepatomegaly, and dysostosis multiplex, 5 besides many immune‐related dysfunc‐ tions, for which a particular interest has been recently concentrated on the involvement of human α‐fucosidases with chronic inflamma‐ tory diseases, immune disorders, and autoimmunity. 6 In the pediat‐ ric population, diagnosis of autoimmune disorders, such as Sjögren's Received: 12 November 2018 | Revised: 2 May 2019 | Accepted: 23 May 2019 DOI: 10.1111/1756‐185X.13639 ORIGINAL ARTICLE Plasma α‐L‐fucosidase‐1 in patients with Sjögren’s syndrome and other rheumatic disorders Ildikó Endreffy 1 | Geir Bjørklund 2 | Attila Bartha 3 | Salvatore Chirumbolo 4 | Maryam Dadar 5 | Ágnes Fényi 6 1 Department of Pediatrics, Jósa András County Hospital, Nyíregyháza, Hungary 2 Council for Nutritional and Environmental Medicine, Mo i Rana, Norway 3 Department of Rheumatology, Jósa András County Hospital, Nyíregyháza, Hungary 4 Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy 5 Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran 6 Department of Otolaryngology, Head and Neck Surgery, Semmelweis University, Budapest, Hungary Correspondence Geir Bjørklund, Council for Nutritional and Environmental Medicine, Toften 24, 8610 Mo i Rana, Norway. Email: bjorklund@conem.org Abstract Background: Human α‐fucosidase (EC 3.2.1.51) is a hydrolase the importance of which has been increasing in the latest years. However, data about its plasma level in children with autoimmune disorders, particularly Sjögren's syndrome (SS), are lack‐ ing. In this study, the plasma activity of L‐α‐fucosidase‐1 (α‐L‐FUCA‐1) was assayed in hospitalized children and adults and its association with SS and other rheumatic disorders further evaluated. Methods: In total 73 Hungarian hospitalized patients, 32 children (2.5‐10 years) and 41 adults (32‐68 years), were enrolled in the study and underwent plasma assay of α‐L‐FUCA1 activity. Linear regression, Durbin‐Watson (DW), and Pearson tests were evaluated to investigate the relationship between α‐L‐FUCA‐1 plasma levels and au‐ toimmune manifestations. Results: α‐L‐FUCA‐1 correlated with SS both in children (2‐sided t test, P = 0.0023) and in adults (2‐sided t test, P = 0.00035). Linear regressions showed that in other rheumatic disorders, α‐L‐FUCA1 did not show any differential distribution related to the particular pathology (r = 0.2042, P = 0.1531, DW test = 2.2139 positive), while this trend was radically opposite for patients with SS (r = 0.1462, P = 0.0032, DW test = 1.3664, negative). Conclusions: Alterations in plasma level of α‐L‐FUCA‐1 were significantly associated with SS. This preliminary result should encourage further research on α‐L‐FUCA‐1 as a possible differential serological marker of SS. KEYWORDS pediatric population, plasma rheumatoid arthritis, Sjögren syndrome, α‐L‐FUCA‐1