Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Renal nutcracker syndrome ?
    ### Response:
    Renal nutcracker syndrome (NCS) is a condition that occurs when the left renal vein (the vein that carries blood purified by the left kidney) becomes compressed. The signs and symptoms of the condition can vary from person to person. Some affected people may be asymptomatic while others develop severe and persistent symptoms.
    