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Content is anchored to trusted sources where available, but Compass has not yet been clinically reviewed. It provides general information rather than medical advice.

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Genetics and inheritance

Penetrance

How likely it is that someone carrying a genetic change will actually develop the condition.

What it means

Carrying a change is not the same as developing something. If penetrance is incomplete, some people with the change never develop the condition, and it can appear to skip generations. It is the reason a genetic test result is harder to read than it looks.

Why you might hear it

  • It is central to what a predictive test result can and cannot tell a relative.
  • It explains why a family history can look absent when a change is present.

People who may help

Where Compass goes into this

About this explanation

These are plain explanations of words you may come across, not advice about your own situation. Where a word matters to a decision, the question pages go into it properly, and your own team is the place to take it.