Effects of a genetic variant

Why is it that the same genetic variant can have different effects for different people?



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The same genetic variant can cause different effects from person to person. This can be due to either the penetrance or expressivity of the variant.

Sometimes, everyone who inherits a particular disease-causing variant will develop the disease it is associated with – this is known as a condition with complete penetrance. Other conditions have reduced penetrance – meaning that not everyone who inherits them will go on to develop disease. The reasons for this are unclear, but are likely a combination of genetic and environmental factors. It’s not currently possible to predict who will develop a disease with reduced penetrance and who will not.

The signs and symptoms of a genetic condition can vary from person to person – this is known as variable expressivity. Some people with a genetic variant may only have mild symptoms, while others with a variant in the same gene develop life threatening complications. The reasons for variable expressivity are also unclear, but are probably a combination of genetic and environmental factors.


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Kinghorn Centre for Clinical Genomics, August 2018. 
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