Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to generalized arterial calcification of infancy ?
    ### Response:
    In about two-thirds of cases, GACI is caused by mutations in the ENPP1 gene. This gene provides instructions for making a protein that helps break down a molecule called adenosine triphosphate (ATP), specifically when it is found outside the cell (extracellular).
    