The causative organism in CJD is difficult to identify because no foreign ribonucleic acid or deoxyribonucleic acid has been linked to the disease. CJD is believed to be caused by a specific protein called a prion, which lacks nucleic acids, resists proteolytic digestion, and spontaneously aggregates in the brain. There are three major categories of CJD: It is estimated that up to 85% of cases are sporadic; 5% to 15% are familial, with an autosomal dominant pattern of inheritance; and the remaining cases are categorized as “acquired CJD.” Although CJD isn’t transmitted by normal casual contact, human-to-human transmission can occur as a result of certain medical procedures, such as corneal and cadaveric dura mater grafts. Isolated cases have resulted from childhood treatment with harvested human growth hormone and from improper decontamination of neurosurgical instruments and brain electrodes.

CJD typically affects adults ages 40 to 65 and occurs in more than 50 countries worldwide. Men and women are affected equally. In people younger than age 30, the incidence is 5 in 1 billion; in all other age groups, the incidence is 1 in 1 million. In the United States, an estimated 200 cases are diagnosed each year.