Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) COL4A1-related brain small-vessel disease ?
    ### Response:
    COL4A1-related brain small-vessel disease is part of a group of conditions called the COL4A1-related disorders. The conditions in this group have a range of signs and symptoms that involve fragile blood vessels. COL4A1-related brain small-vessel disease is characterized by weakening of the blood vessels in the brain.
    