Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Best vitelliform macular dystrophy ?
    ### Response:
    What causes Best vitelliform macular dystrophy? Best vitelliform macular dystrophy (BVMD) is caused by changes (mutations) in the BEST1 gene. This gene gives the body instructions for making a protein called bestrophin. Bestrophin acts as a channel that controls the movement of chloride ions within the retina.
    