Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Henoch-Schonlein purpura ?
    ### Response:
    Henoch-Schonlein purpura (HSP) is a disease that involves purple spots on the skin (purpura), joint pain, digestive problems, and glomerulonephritis (a type of kidney disorder). While the cause of this condition is not fully understood, it may develop as an immune response to an infection.
    