Multisystem inflammatory syndrome in children (MIS‐C) is a rare, but severe complication of coronavirus disease 2019 (COVID‐19). It develops approximately 4 weeks after severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection and involves hyperinflammation with multisystem injury, commonly progressing to shock. The exact pathomechanism of MIS‐C is not known, but immunological dysregulation leading to cytokine storm plays a central role. In response to the emergence of MIS‐C, the European Academy of Allergy and Clinical Immunology (EAACI) established a task force (TF) within the Immunology Section in May 2021. With the use of an online Delphi process, TF formulated clinical statements regarding immunological background of MIS‐C, diagnosis, treatment, follow‐up, and the role of COVID‐19 vaccinations. MIS‐C case definition is broad, and diagnosis is made based on clinical presentation. The immunological mechanism leading to MIS‐C is unclear and depends on activating multiple pathways leading to hyperinflammation. Current management of MIS‐C relies on supportive care in combination with immunosuppressive and/or immunomodulatory agents. The most frequently used agents are systemic steroids and intravenous immunoglobulin. Despite good overall short‐term outcome, MIS‐C patients should be followed‐up at regular intervals after discharge, focusing on cardiac disease, organ damage, and inflammatory activity. COVID‐19 vaccination is a safe and effective measure to prevent MIS‐C. In anticipation of further research, we propose a convenient and clinically practical algorithm for managing MIS‐C developed by the Immunology Section of the EAACI.

Pediatric inflammatory multisystem syndrome (PIMS) is a new entity in children, likely associated with previous coronavirus disease 19 (COVID-19) infection. Most of the reports about PIMS come from countries particularly hit by the COVID-19 pandemic. Our aim was to investigate the nature of inflammatory syndromes in Poland (country with low COVID-19 prevalence) and to perceive the emergence of PIMS in our country. On 25 May 2020, we launched a nationwide survey of inflammatory syndromes in children for retrospective (since 4 March 2020) and prospective data collection. Up to 28 July, 39 reported children met the inclusion criteria. We stratified them according to age (<5 and ≥ 5 years old) and COVID-19 status. The majority of children had clinical and laboratory features of Kawasaki disease, probably non-associated with COVID-19. However, children ≥5 years of age had PIMS characteristics, and nine children had COVID-19 confirmation. This is, to our knowledge, the first report of the PIMS register from a country with a low COVID-19 prevalence, and it proves that PIMS may emerge in any area involved in the COVID-19 pandemic. In a context of limited COVID-19 testing availability, other risk factors of PIMS, e.g., older age, should be considered in the differential diagnosis of inflammatory syndromes in children.

Background: Kawasaki disease (KD) is an acute self-limited febrile vasculitis that mainly affects young children. Coronary artery involvement is the most serious complication in children with KD. It is currently the leading cause of acquired cardiac disease in children from developed countries. Literature data indicate a significant role of genetic susceptibility to KD.Objective: The aim of this study was to perform the first Genome-Wide Association Study (GWAS) in a population of Polish children with KD and identify susceptible genes involved in the pathogenesis of KD.Materials and Methods: The blood samples of Kawasaki disease patients (n = 119) were collected between 2016 and 2020, isolated and stored at the Department of Pediatrics, Nutrition and Metabolic Diseases, Children's Memorial Health Institute in Warsaw. The control group was based on Polish donors (n = 6,071) registered as the POPULOUS collection at the Biobank Lab of The Department of Molecular Biophysics in University of Lodz. DNA samples were genotyped for 558,231 Single Nucleotide Polymorphisms (SNPs) using the 24 × 1 Infinium HTS Human Core Exome microarrays according to the protocol provided by the manufacturer. In order to discover and verify genetic risk-factors for KD, association analysis was carried out using PLINK 1.9.Results: Of all 164,395 variants, 5 were shown to occur statistically (p_adjusted < 0.05) more frequent in Kawasaki disease patients than in controls. Those are: rs12037447 in non-coding sequence (p_adjusted = 8.329 × 10⁻⁴, OR = 8.697, 95% CI; 3.629–20.84) and rs146732504 in KIF25 (p_adjusted = 0.007354, OR = 11.42, 95% CI; 3.79–34.43), rs151078858 in PTPRJ (p_adjusted = 0.04513, OR = 8.116, 95% CI; 3.134–21.01), rs55723436 in SPECC1L (p_adjusted = 0.04596, OR = 5.596, 95% CI; 2.669–11.74), rs6094136 in RPN2 (p_adjusted = 0.04755, OR = 10.08, 95% CI; 3.385–30.01) genes.Conclusion: Polymorphisms of genes KIF25, PTRPJ, SPECC1L, RNP2 may be linked with the incidence of Kawasaki disease in Polish children.

Background: Renalase is kidney-derived molecule initially considered as catecholamine-inactivating enzyme. However, recent studies suggest that renalase exerts potent cardio- and nephroprotective actions, not related to its enzymatic activity. Purpose: To assess renalase level in children with chronic kidney disease (CKD). Material and methods: Serum renalase, BMI, arterial stiffness, peripheral and central blood pressure, intima-media thickness (IMT), medications, and biochemical parameters were analyzed in 38 children with CKD (12.23 ± 4.19 years) (stage G2-5). Control group consisted of 38 healthy children. Results: In the study group, GFR was 25.74 ± 8.94 mL/min/1.73 m²; 6 children were dialyzed; 26 had arterial hypertension. Renalase level was higher in the study group compared to control group (p < 0.001). In CKD children renalase correlated (p < 0.05) with BMI Z-score (r = –0.36), alfacalcidol dose (r = 0.41), GFR (r = –0.69), hemoglobin (r = –0.48), total cholesterol (r = 0.35), LDL-cholesterol (r = 0.36), triglycerides (r = 0.52), phosphate (r = 0.35), calcium-phosphorus product (r = 0.35), parathormone (r = 0.58), and pulse wave velocity Z-score (r = 0.42). In multivariate analysis GFR (β = –0.63, p < 0.001), triglycerides (β = 0.59, p = 0.002), and alfacalcidol dose (β = –0.49, p = 0.010) were determinants of renalase. Conclusions: In children with CKD there is a strong correlation between renalase level and CKD stage. Furthermore, in these patients renalase does not correlate with blood pressure but may be a marker of arterial stiffness.