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Adenosine deaminase 2 (ADA2) is a protein with at least two functions. It is a growth factor affecting leukocytes and endothelial cells and an enzyme that influences purine metabolism. This study shows that mutant ADA2 causes polyarteritis nodosa. Polyarteritis nodosa, first described in 1866, 1 is a systemic necrotizing vasculitis that affects medium and small muscular arteries. 2 , 3 The ensuing tissue ischemia can affect any organ, including the skin, musculoskeletal system, kidneys, gastrointestinal tract, and the cardiovascular and nervous systems. Polyarteritis nodosa is usually diagnosed in middle age or later but can appear in childhood. 2 , 4 , 5 The diagnosis remains challenging despite classification criteria for adults 6 and children, 7 because polyarteritis nodosa frequently presents with nonspecific constitutional symptoms, and organ involvement and disease severity are highly varied. Polyarteritis nodosa is most often primary, but in adults it may be associated . . .

An elevated expression of the alloantigen D8/17 on B lymphocytes has been previously proposed as a susceptibility marker in rheumatic fever. The aim of the study was to investigate the presence of the D8/17 marker on B lymphocytes in poststreptococcal reactive arthritis (PSRA). The study sample included 19 patients (15 boys, 4 girls; mean age 11.7 +/- 5.4 years) who were diagnosed with PSRA (mean age at diagnosis, 9.4 +/- 5.6 years) and 18 healthy controls (10 boys and 8 girls) matched for ethnic background. B-cell D8/17 expression was tested by flow cytometry assay using monoclonal antibodies. Laboratory results showed a higher expression of D8/17 in the patient group (23.1 +/- 10.4%, range 11.6-51.9%) than in the control group (17.1 +/- 8.2%, range 7.1-35.7) in controls; this difference was statistically significant after log transformation of the data (P = 0.035). The high rate of expression of the D8/17 marker in patients with PSRA suggests that RF and PSRA share the same genetic susceptibility.

In recent years, antiphospholipid syndrome (APS) has been increasingly recognised in various paediatric autoimmune and nonautoimmune diseases, but the relatively low prevalence and heterogeneity of APS in childhood made it very difficult to study in a systematic way. The project of an international registry of paediatric patients with APS (the Ped-APS Registry) was initiated in 2004 to foster and conduct multicentre, controlled studies with large number of paediatric APS patients. The Ped-APS Registry is organised as a collaborative project of the European Forum on Antiphospholipid Antibodies and Juvenile Systemic Lupus Erythematosus Working Group of the Paediatric Rheumatology European Society. Currently, it documents a standardised clinical, laboratory and therapeutic data of 133 children with antiphospholipid antibodies (aPL)-related thrombosis from 14 countries. The priority projects for future research of the Ped-APS Registry include prospective enrolment of new patients with aPL-related thrombosis, assessment of differences between the paediatric and adult APS, evaluation of proinflammatory genotype as a risk factor for APS manifestations in childhood and evaluation of patients with isolated nonthrombotic aPL-related manifestations.