RLO: Penetrance

• Introduction
• All-or-none phenomenon
• Terminology
• Lifetime & reduced penetrance
• Penetrance quiz
• Time scale

Lifetime & reduced penetrance

Most often, penetrance is described as a lifetime penetrance, meaning the probability that an affected individual will develop the condition over their lifetime. Take, for example, a family with a known BRCA1 mutation. The grandmother, mother and daughter have all been tested and were found to carry the familial mutation.

The grandmother was diagnosed with ovarian cancer at age 40 and daughter was diagnosed with breast cancer at age 37. The mother lived until the age of 80, was never diagnosed with cancer and died of a heart attack. In the case of the mother, the BRCA1 mutation was non-penetrant while in the daughter and grandmother was penetrant. When a genetic condition is thought to ‘skip a generation’, as in this example, the condition has actually shown reduced or incomplete penetrance.