They consist of mandatory and supportive criteria: the mandatory one is the presence of palpable purpura in the absence of thrombocytopenia, while the supportive criteria involve at least one of the following: acute onset of diffuse abdominal pain, acute onset of arthralgia or arthritis, histopathological evidence of leukocytoclastic vasculitis or proliferative glomerulonephritis with IgA deposits and renal involvement documented by proteinuria or hematuria. The gene discussed is CD79A; the disease is hypersensitivity vasculitis.