Approximately 10–15 percent of people with prion disease have a genetic form. Genetic Creutzfeldt-Jakob disease (CJD) is a single gene disorder due to mutations in the prion gene (PRNP) on chromosome 20. Presently more than 20 alterations in the DNA sequence in the gene have been reported. The characteristics of the disease correlate with the different mutation types.
Several other changes in the PRNP gene (called polymorphisms) do not cause prion diseases directly but may affect a person's risk of developing these diseases or alter the course of the disease.
Genetic prion disease follows an autosomal dominant inheritance pattern, which means that if you carry a prion-disease-causing mutation, each of your children has a 50 percent (1 in 2) chance to inherit the same mutation. If genetic prion disease is present in a family, men and women have the same risk to inherit the family mutation. How a mutation is passed on within a family is considered separately from the question of whether or not someone with a mutation will develop the disease.
To add to the complexity of inheritance, a new mutation could occur in the PRNP gene, causing a sporadic case of CJD for that individual, and then become a hereditary genetic disorder for the next generations.