Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation ?
    ### Response:
    Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (commonly referred to as LBSL) is a progressive disorder that affects the brain and spinal cord. Leukoencephalopathy refers to abnormalities in the white matter of the brain, which is tissue containing nerve cell fibers (axons) that transmit nerve impulses.
    