Visual communication aid: Penetrance and expressivity

There is one communication aid available to view and download (.pdf):

• Penetrance and expressivity

Double-sided printing in colour is recommended (but not required). All content is also included below in an accessible format.

More information about these and other VCAs is available in this article.

In genomics, the terms ‘penetrance’ and ‘expressivity’ explain how a genetic change might affect people differently (figure 1).

Penetrance: the proportion of people with a genetic change that show signs or symptoms of a condition.

• If a condition has complete penetrance, this means everyone with the genetic change will develop the condition.
• If it has reduced (incomplete) penetrance, this means some people with the genetic change develop the condition and some do not.

Expressivity: how a condition affects different people.

• Many genetic conditions show different symptoms or severity in different people. This is called variable expressivity.

In conditions with reduced penetrance and variable expressivity:

• Not everyone with the genetic change will be affected.
• Among those who are affected, the symptoms can look different from one person to the next.

Remember, conditions may show variable penetrance or expressivity even between people in the same family with the same genetic change.

Figure 1: Reduced penetrance and variable expressivity

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• Gene change: Changes in a gene or chromosome used to be referred to as ‘mutations.’ Now, they are more commonly called changes, alterations or variants.

For patients

• Unique: Variable Expressivity & Reduced Penetrance (pdf)