Approximately 10-15% of people with prion disease have a genetic form. Genetic 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, 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, meaning that the genetic mutation of the PRNP gene is generally inherited from one parent. If you inherit one abnormal PRNP gene from both parents, then you will usually develop the disease. If you inherit the gene from only one of your parents, then you have a 50:50 chance of developing the disease. You also have a 50% chance of passing it on to your children. Men and women are equally likely to inherit the mutation and to be affected. Family history typically reveals the disorder in sequential generations.
To add to the complexity, a new mutation could occur in the PRNP gene, causing a sporadic case of CJD for that individual, but then becoming a hereditary genetic disorder for the next generations.
