A mutation is a transmissible or heritable change in the nucleotide sequence of the genetic material of a cell or virus. Mutations are either spontaneous, occurring naturally due to errors in DNA or RNA replication, or induced by external agents. When identifying the etiology of a disease and the factors that alter a person's risk for disease, epidemiologists must often determine the unique contributions of environmental and genetic factors. Increasingly, we are made aware of the importance of mutations in the development of disease and the evolution of pathogens.

Mutations are often involved in the etiology of diseases attributed to host genetic factors. Mutations of the breast cancer susceptibility genes BRCA1 or BRCA2 result in an increased risk of developing breast cancer or ovarian cancer and ...