CD79A and Arthritis: Clinical criteria for HSP according to EULAR include (1) purpura (mandatory criterion) or petechiae, with lower limb predominance, (not related to thrombocytopenia); (2) abdominal pain (may intussusception and gastrointestinal bleeding); (3) histological changes showing leucocytoclastic vasculitis with predominant IgA deposit or proliferative glomerulonephritis with predominant IgA deposit; (4) arthritis or arthralgias; (5) renal involvement with hematuria and/or proteinuria.