Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) familial HDL deficiency ?
    ### Response:
    Familial HDL deficiency is a condition characterized by low levels of high-density lipoprotein (HDL) in the blood. HDL is a molecule that transports cholesterol and certain fats called phospholipids through the bloodstream from the body's tissues to the liver.
    