1.   Perhaps gene therapy could prevent the mutation of the prion gene that causes hereditary brain disease.

2.   And when the prion gene was reintroduced into the knock-out mice, they again became susceptible to infection.

3.   Any animals without the prion gene could not easily be infected with the virus.

4.   A family may pass on a mutated prion gene, and in that way be susceptible to Creutzfeldt-Jakob disease, for instance.

5.   The other mouse experiment, in which mice with mutant prion genes spontaneously developed scrapie, also can be explained without invoking prions as infectious agents, critics say.

6.   They also found that they could put a mutant prion gene into mice and the animals would spontaneously develop scrapie.

7.   What about the prion gene?