Answer from: Douglas Lester, PhD, MSc, BSc (Hons)
In genetics, some single-gene mutations do not show 100% penetrance. The classic example of this is the Bracken gene mutations in humans. It usually affects women, but it also affects men. If they’ve got a bad mutation, you have a 90% chance of developing breast cancer. For most people, this risk is too high, and they are offered a double mastectomy. Quite a few fertility gene mutations may not be 100% penetrant; for example, a new mutation was found in inversion in males of Eastern Polish, Czech, and Slovakian. They’ve got an inversion of 1.6 million records on the Y chromosome. Most of these males have normal fertility. However, if they’ve got this inversion and they’re an older father, they are eight times more likely to have other DNA letter changes in that region, and that causes infertility. Geneticists, therefore, offer percentage risk scores; the patient can then decide their own course of action based on the risk score.
Genetic disease risk - what does it mean for patients?
Genetic condition risk factors include older age in the woman, a family history of genetic diseases or being a carrier of a genetic condition, a previous miscarriage caused by a genetic defect, or a baby/child with a genetic disease.