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There are several biological mechanisms that explain why a genetic condition may remain undetected for years.
1. Progressive accumulation of cellular damage
Some genetic conditions cause gradual damage to cells, tissues or organs. The effects may initially be too small to produce noticeable symptoms. As damage accumulates, the individual may eventually develop clinical manifestations.
2. Age-dependent gene expression
Certain genes play important roles during specific stages of life. A genetic alteration may have little noticeable effect during childhood but become clinically significant during adulthood.
3. Incomplete penetrance
Penetrance refers to the proportion of individuals carrying a particular genetic variant who actually develop the associated condition.
For example, two individuals may carry the same pathogenic variant, but one may develop the disease while the other remains asymptomatic throughout life.
4. The second-hit mechanism
Some genetic conditions, particularly certain cancers, require more than one genetic event.
For example, in hereditary retinoblastoma, an individual may inherit one altered copy of the RB1 gene. A second acquired alteration in the remaining functional copy can lead to tumour development.
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