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How can a person carry a dominant mutation without showing symptoms?
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human genetic disease
Photomicrograph of the BRCA2 tumor suppressor gene on chromosome 13 of the human genome. Inactivation of this growth-regulating gene is associated with a higher risk of developing breast cancer.
A person can carry a dominant mutation without showing symptoms due to a phenomenon known as nonpenetrance. In genetics, penetrance refers to the frequency with which a specific trait or disease manifests in individuals who carry the corresponding gene. When an individual possesses a dominant, disease-causing mutation but exhibits no apparent phenotypic abnormalities, they are described as nonpenetrant.123
Several factors contribute to this lack of expression:
- Epistatic Genes: Some genes, known as epistatic genes, can mask the expression of other genes. The presence of these genes can prevent the manifestation of a dominant mutation, resulting in an individual who is phenotypically normal despite carrying the deleterious gene.2
- Modifying Effects: The clinical severity of genetic disorders can vary dramatically due to the modifying effects of other genes or environmental factors. These influences can suppress the expression of a mutation in some individuals while allowing it to manifest in others.1
Although nonpenetrant individuals appear healthy, they remain carriers of the mutation and are capable of passing it to their offspring, who may then exhibit the full-blown disease.12