Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to spinal muscular atrophy ?
    ### Response:
    Mutations in the SMN1, UBA1, DYNC1H1, and VAPB genes cause spinal muscular atrophy. Extra copies of the SMN2 gene modify the severity of spinal muscular atrophy.  The SMN1 and SMN2 genes provide instructions for making a protein called the survival motor neuron (SMN) protein.
    