Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Tay-Sachs disease ?
    ### Response:
    Tay-Sachs disease is a rare inherited disorder that causes progressive destruction of nerve cells in the brain and spinal cord. Tay-Sachs is caused by the absence of a vital enzyme called hexosaminidase-A (Hex-A). Without Hex-A, a fatty substance, or lipid, called GM2 ganglioside accumulates abnormally in cells, especially in the nerve cells of the brain.
    