Significance: To determine whether genetic variation within the MHC locus influences the risk of developing systemic juvenile idiopathic arthritis (sJIA), we examined a dense set of MHC region single nucleotide polymorphisms, classic HLA alleles, and the individual amino acids of HLA molecules in nine independent sJIA case-control populations. Association testing revealed that genetic variants within the MHC class II gene cluster significantly influenced sJIA risk in every study population. The strongest risk factor for sJIA wasHLA-DRB1*11, which conferred at least a two-fold increase in disease risk in each population studied. These data implicate the interaction of antigen presenting cells with T cells in the pathogenesis of sJIA.

Objectives Juvenile idiopathic arthritis (JIA) is a heterogeneous group of conditions unified by the presence of chronic childhood arthritis without an identifiable cause. Systemic JIA (sJIA) is a rare form of JIA characterised by systemic inflammation. sJIA is distinguished from other forms of JIA by unique clinical features and treatment responses that are similar to autoinflammatory diseases. However, approximately half of children with sJIA develop destructive, long-standing arthritis that appears similar to other forms of JIA. Using genomic approaches, we sought to gain novel insights into the pathophysiology of sJIA and its relationship with other forms of JIA. Methods We performed a genome-wide association study of 770 children with sJIA collected in nine countries by the International Childhood Arthritis Genetics Consortium. Single nucleotide polymorphisms were tested for association with sJIA. Weighted genetic risk scores were used to compare the genetic architecture of sJIA with other JIA subtypes. Results The major histocompatibility complex locus and a locus on chromosome 1 each showed association with sJIA exceeding the threshold for genome-wide significance, while 23 other novel loci were suggestive of association with sJIA. Using a combination of genetic and statistical approaches, we found no evidence of shared genetic architecture between sJIA and other common JIA subtypes. Conclusions The lack of shared genetic risk factors between sJIA and other JIA subtypes supports the hypothesis that sJIA is a unique disease process and argues for a different classification framework. Research to improve sJIA therapy should target its unique genetics and specific pathophysiological pathways.

Background: Recurrent pericarditis (RP) is a complication (15–30%) of acute pericarditis with an unknown etiology. Treatment regimen consists of a combination of non-steroidal anti-inflammatory drugs (NSAIDs) and colchicine, with the addition of corticosteroids in resistant or intolerant cases. In the last decade anakinra was shown as an effective treatment in patients with colchicine resistant and steroid-dependent RP, initially in anecdotal reports in children and more recently in a randomized trial. Canakinumab is a monoclonal antibody selectively blocking IL-1β and its use is only anecdotally reported to treat pericarditis. We report two pediatric patients with refractory recurrent pericarditis, who presented an optimal response to anakinra treatment but prompt relapse after switch to canakinumab. Case presentation: The first patient is a girl with Recurrent Pericarditis started in April 2015, after heart surgery. NSAIDs and oral steroids were started, with prompt relapse after steroid suspension. The child showed a steroid-dependent RP; anakinra was therefore started with excellent response, but discontinued after 2 weeks for local reactions. In July 2016 therapy with canakinumab was started. She experienced four relapses during canakinumab therapy despite dosage increase and steroid treatment. In January 2018 a procedure of desensitization from anakinra was performed, successfully. Anakinra as monotherapy is currently ongoing, without any sign of flare. The second patient is a girl with an idiopathic RP, who showed an initial benefit from NSAIDs and colchicine. However, 10 days after the first episode a relapse occurred and therapy with anakinra was established. Two months later, while being in complete remission, anakinra was replaced with canakinumab due to patient’s poor compliance to daily injections. She experienced a relapse requiring steroids 10 days after the first canakinumab injection. Anakinra was subsequently re-started with complete remission, persisting after 24 months follow-up. Conclusions: We describe two cases of failure of the treatment with anti-IL-1β monoclonal antibodies in steroid- dependent idiopathic RP. This anecdotal and preliminary observation suggests a different efficacy of the two IL-1 blockers in the management of RP and support a possible pivotal role of IL-1α in the pathogenesis of this condition.

Multisystem inflammatory syndrome in children (MIS-C) evolves in some pediatric patients following acute infection with SARS-CoV-2 by hitherto unknown mechanisms. Whereas acute-COVID-19 severity and outcomes were previously correlated with Notch4 expression on Tregs, here, we show that Tregs in MIS-C were destabilized through a Notch1-dependent mechanism. Genetic analysis revealed that patients with MIS-C had enrichment of rare deleterious variants affecting inflammation and autoimmunity pathways, including dominant-negative mutations in the Notch1 regulators NUMB and NUMBL leading to Notch1 upregulation. Notch1 signaling in Tregs induced CD22, leading to their destabilization in a mTORC1-dependent manner and to the promotion of systemic inflammation. These results identify a Notch1/CD22 signaling axis that disrupts Treg function in MIS-C and point to distinct immune checkpoints controlled by individual Treg Notch receptors that shape the inflammatory outcome in SARS-CoV-2 infection.