Crouzon syndrome

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.^[1] For this reason, Crouzon syndrome has been described by some as having variable penetrance and expressivity, even within families.^[2][1][3] 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.^[1] 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

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 mutation.

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.

To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. Online directories are provided by the American College of Medical Genetics and the National Society of Genetic Counselors. If you need additional help, contact a GARD Information Specialist. You can also learn more about genetic consultations from Genetics Home Reference.