The brain disease vCJD was caused by eating beef from cattle infected with BSE. Susceptibility to this type of disease amongst humans is associated with a particular gene. There are two variants of this gene – M and V, so there are three possible combinations that we can inherit – M-M, M-V and V-V. All infections so far in the UK have been in young people with the M-M combination. Most victims of a similar disease in Papua New Guinea also had the M-M combination and were also young, but a group who developed it later in life all had the M-V combination. Therefore the gene variants one inherits determine the incubation period for such diseases. So there will be two further outbreaks of vCJD, as those who consumed infected beef grow older.