Mandatory criteriona:•Purpura or petechiae with lower limb predominance (not related to thrombocytopenia) and/or•Any biopsy showing predominant IgA deposition with or without leukocytoclastic vasculitisThe presence of at least one of the following three features:•Abdominal pain with acute onsetb•Arthritis or arthralgia of acute onset•Renal involvement (hematuria and/or proteinuria)c. The gene discussed is CD79A; the disease is arthritic joint disease.