Human prion diseases.

The past year has seen considerable advances in our understanding of the prion diseases, and there is increasing acceptance that the transmissible agent in these diseases may be an abnormal isoform of a normal host encoded protein. Molecular genetic studies have led to a new appreciation of the phenotypic spectrum of the prion diseases as the inherited forms of these conditions can now be diagnosed by a direct gene test. The conundrum of how a disease can be both inherited and transmissible is beginning to make sense.