Approximately 10 to 15 per cent of CJD cases are inherited. These familial cases exhibit a mutation in the gene coding for the prion protein. Genetic factors are thought to be responsible for the elevated numbers of CJD cases in some communities in Czechoslovakia and Chile, as well as among Libyan-born Jews.
Genetic analysis has been well studied in the familial form of CJD. The prion protein in familial cases is the same in each family member that has it, and different in all other families. Sometimes the difference is as small as one amino acid, but these differences can be used to determine the pedigree of the prion. In the familial disease there is are mutations in the gene encoding the normal protein such that the protein tends to fold in the abnormal way and tends to pile up into aggregates in brain cells with lethal onsequences.