nonpenetrance
(non-PEH-neh-trunts)
A term that describes when a person has a disease-causing mutation (change) in a gene but never develops the disease. For example, a woman may have a certain BRCA1 gene mutation that increases her risk of breast cancer, but because the gene mutation is nonpenetrant, she never develops breast cancer. However, she can still pass the BRCA1 gene mutation to her children, who may develop cancer.