Almost all people with a mutation
known to cause Crouzon syndrome
have features of the condition. However, in at least one family, it appeared that the responsible mutation did not affect every family member who had it.
For this reason, Crouzon syndrome has been described by some as having variable penetrance and expressivity
, even within families.
When a condition has variable (or reduced) penetrance, it means that not every person with a mutation in the responsible gene
will have apparent signs and symptoms of the condition. When a condition has variable expressivity
, it means that not all people who do have features will be affected the same way - there is a range of possible features and severity. While extremely uncommon, it may be possible for family members with a mutation to "appear" unaffected, with very mild or unnoticeable features.
Therefore, whether an unaffected sibling is at risk to have an affected child may depend on whether the sibling has a mutation
in the responsible gene.
If an apparently unaffected sibling is confirmed to not have the mutation that is present in an affected family member, he/she is not considered at risk to have an affected child. In other words, a person cannot pass on a mutation that he/she does not have. Based on most reports in the literature, people without features of Crouzon syndrome typically do not carry a mutation in the responsible gene
If an apparently unaffected sibling does have the mutation that is present in an affected family member, he/she has a 50% (1 in 2) chance to pass the mutation on to each child. In this case, even though the sibling does not have apparent features of the condition, it would not be possible to predict whether a child that inherits the mutation will be affected, or how severely he/she may be affected.
If the specific mutation causing Crouzon syndrome has been identified in an affected family member, other family members can have genetic testing
to determine whether they carry the mutation and are at risk for passing the mutation on to their children.
People with personal questions about genetic risks and genetic testing are encouraged to speak with a genetic counselor
or other genetics professional. A genetics professional can help by:
- thoroughly evaluating the family history
- addressing questions and concerns
- assessing recurrence risks
- facilitating genetic testing if desired
- discussing reproductive options
Last updated: 6/8/2016
Crouzon syndrome is inherited
in an autosomal dominant
manner. This means that having a change (mutation
) in only one copy of the responsible gene
in each cell
is enough to cause features of the condition.
There is nothing that either parent can do, before or during a pregnancy, to cause a child to be born with Crouzon syndrome.
In some cases, an affected person inherits the mutated gene from an affected parent. In other cases, the mutation occurs for the first time in a person with no family history of the condition. This is called a de novo
When a person with a mutation that causes an autosomal dominant condition has children, each child has a 50% (1 in 2) chance to inherit that mutation.
Last updated: 6/8/2016
Last updated: 12/6/2017
We hope this information is helpful. We strongly recommend you discuss this information with your doctor. If you still have questions, please
GARD Information Specialist
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