encephalopathy and by eating their brains
they spread the disease to others.
We also recognize sporadic spongiform encephalopathies.
These are TSEs that arise with no warning
whatsoever, they don't seem to be transmitted.
And one of them is called sporadic Creutzfeldt-Jacob
disease, this affects about 1 to 2 people
per million worldwide. They're typically 50
to 70 years old of age, and this accounts
for most of the TSE that we find globally,
about 65% of the cases. In sporadic CJ, the
disease appears with no warning, there is
no epidemiological indication that the individual
has not consumed anything or received any
transplant that would cause the disease, they
have normal prnp genes, so there's no mutation
associated with it, it just is sporadic as
the name would suggest. So we think what happens
here is that the normal prion protein of these
individuals simply starts misfolding spontaneously.
And as soon as you have a little bit of misfolded
prion protein in you, it then catalyzes the
conversion of your other protein and you develop
the disease. So if you develop a sporadic
CJD, you can transmit it to other people and
that will cause an infectious form to arise.
So you can imagine that a person who is incubating
a sporadic CJD, there are many years of incubation
involved, during which you have no symptoms.
If you made some kind of a tissue or blood
donation during that period, you could transmit
the disease to others and in fact this disease
has been known to be transmitted as I've said
from corneal transplants, hormonal transplants
and so forth. We think that kuru may have
originally arisen in New Guinea from the first
case many years ago, from a sporadic case
of CJD, that person died, their brain was
consumed and then that initiated the infectious
mode of transmission.
And finally, we have a familial or genetic
TSE, and this as the name would indicate is
associated with a mutation in the gene encoding
prion protein, and this is an autosomal dominant
mutation and by sequencing the genome of people
who have developed TSEs, we know exactly what
kind of amino acid changes are associated
with development of the disease. So you can
now go and have this gene sequence, then know
if you're at risk for developing a TSE. And
when these individuals develop this genetic
TSE, they began to develop symptoms of the
disease but before that, again, there is a
long incubation period, during that time if
they donate corneas or organs or blood products,
they can spread the disease to someone else.