GENE A schematic of the PrP gene is shown in Figure 1. There are 4 human diseases classified as TSEs. Since the widespread cessation of cannibalism in PNG, kuru has declined dramatically, and is believed to have been wiped out. Cases which still arise are thought to be due to the long incubation time of the disease, in people who engaged in cannibalism earlier this century. CJD is the most common TSE diagnosed in humans, and falls into three categories, iatrogenic, inherited, and sporadic.
Iatrogenic cases are extremely rare.
Inherited CJD is caused by pathogenic polymorphisms in the human PrP gene. Such genetic lesions tend to be dominant although of variable penetrance, although it is possible given the long incubation times of the disease that asymptomatic people with a particular genetic lesion are dying of old age prior to onset of disease. Indeed, the former can be considered a sub-class of the latter. Whether BSE can or will transmit to humans remains unknown at this time, with estimates of human infection ranging from 0 to 10 million. However, much more research needs to be done before the transmission of BSE to humans is proven.