The variation in the number of octarepeat units (PHGGGWGQ) in the PRNP gene is another genetic marker that can be used to study the susceptibility/resistance of cervids to CWD, like as been done in scrapie, BSE and CJD studies [34–36], but so far no variation has been found in cervids studies [35]. The gene discussed is PRNP; the disease is scrapie.