How is Cowden syndrome inherited?
We all have two copies of every gene, including two PTEN genes. We inherit half of our genetic information from our mom and half from our dad, so one of our PTEN genes is inherited from our mother, and the other is inherited from our father. If a parent has Cowden syndrome, there is a 50% chance that each of his or her children will also have Cowden syndrome. This is called autosomal dominant inheritance. A person only needs to inherit one copy of a nonfunctioning, or mutated, PTEN gene to have Cowden syndrome.
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What does it mean to have a "variant of uncertain significance" with Cowden syndrome?
It's not uncommon to find a genetic difference in the PTEN gene that we don't know much about. We call this a "variant of unknown significance" or a VUS. This means that a genetic change was found that we do not fully understand. In other words, this genetic change may cause Cowden syndrome or it may be a normal variation. We need more data to be sure. A genetic counselor or geneticist may be able to help explain what this result means in your particular situation. Over time, scientists may learn more about variants of unknown significance. It is important to check with your healthcare provider on an annual basis for updates on the VUS. Over time, scientists may learn enough about the VUS to determine if a variant is associated with an increased risk for cancer or if the finding is just a normal variation that is harmless.
What is the chance that my child will have Cowden syndrome if his half-sibling had a PTEN mutation?
A PTEN mutation can run in families and and when it does it will be inherited in an autosomal dominant pattern. This means that if a parent is found to have a mutation in that gene, each of their children have a 50% chance of inheriting it. The risk that a child will have the PTEN mutation if a half sibling is known to have the mutation is an good case study to explain how the autosomal dominant pattern of inheritance works. For purposes of this explanation, let's assume that you have a donor-conceived child and you just learned that your child's half sibling has a PTEN mutation with an associated developmental delay.
You would likely be concerned that the donor carries the PTEN mutation making it possible that your child also inherited the mutation but remember, there is also the possibility that your child's half sibling inherited the PTEN mutation from the other parent. If that were the case, your child would not be at increased risk to have a mutation in the PTEN gene. Even if the donor DOES have the mutation, your child would have a 50% chance NOT to have the PTEN mutation.
Cowden syndrome (the syndrome associated with PTEN mutations) is likely under diagnosed because the symptoms aren't always picked up by physicians because they can be so mild. Because of this, the actual number of isolated cases (individuals with no obvious family history) compared to familial cases (defined as two or more related affected individuals) isn't well known. But, it is believed that most cases of Cowden syndrome (CS) are appearing for the first time in the family due to de novo mutations. Between 10%-50% of individuals with CS have an affected parent.
The most common sign of CS in both children and adults is having a head circumference that is bigger than 97% of people their age and of the same sex (macrocephaly). If you know that your child's head is smaller than the 97th percentile for their age, that is one piece of information leaning towards them not having the PTEN mutation.
If the donor is found to carry the PTEN mutation, a genetic counselor would be a great person to talk to regarding ordering genetic testing for your child, the risks associated, and the appropriate management/surveillance. You can use the Find a Genetic Counselor' tool [/link]to find a genetic nurse or counselor in your area.
- Ask a ThinkGenetic Counselor, November 7, 2016