Final answer:
HGH injections were once a cause of CJD because the hormones were taken from the pituitary glands of cadavers, some of which were affected by CJD, which led to the disease being transmitted to patients.
Step-by-step explanation:
The reason why human growth hormone (HGH) injections were once a cause of Creutzfeldt-Jakob Disease (CJD) stems from the method of obtaining HGH. Initially, HGH was derived from the pituitary glands of cadavers. Unfortunately, some of these glands came from individuals who were unknowingly affected by CJD. This resulted in the inadvertent transmission of CJD when the extracted hormones were injected into patients for treatment of growth disorders. After realizing this risk, medical practices changed. Instead of using hormones from cadavers, recombinant DNA technology was employed to produce HGH in a laboratory setting, thus eliminating the risk of transmitting CJD and other diseases through HGH therapy.