What can genetic testing tell you about NF1?
If you, your partner or child has neurofibromatosis type 1 (NF1) (say: noor-oh-fie-broh-muh-TOE-sis), or your doctor suspects NF1, your doctor or genetic counsellor may talk to you about genetic testing.
Genetic testing is also called molecular or DNA testing.
Most people with a clinical diagnosis of NF1 will have a mutation (change) in a gene called Neurofibromin, also called the NF1 gene. A clinical diagnosis is made by a doctor looking for signs of NF1 in your child's skin, eyes or bones.
Your child will need to give a blood sample
To do a genetic test, your child's doctor will take a small blood sample from your child, about one teaspoon (5 mL) of blood. A lab will study the DNA in the blood and look for a mutation in the NF1 gene. It can take from one to two months to get the test results back.
Who should have genetic testing
Genetic testing can be helpful in the following situations:
- If the doctor suspects a young child has NF1, but the child is not showing enough signs to confirm the diagnosis.
- To identify a mutation so that other family members who are at risk can be tested.
- If a couple wishes to consider prenatal diagnosis in a current or future pregnancy.
- To confirm a diagnosis in a case that is difficult to diagnose with a clinical exam.
Possible results of a genetic test for NF1
Genetic testing can be very useful, but the results are not always clear. There are three possible test results from genetic testing for NF1: positive, negative and inconclusive.
Positive: The test found a mutation in the child's NF1 gene
A positive test result confirms NF1. If the test is positive, your child has NF1. This means a mutation was found in your child's NF1 gene.
A positive test result cannot tell you how severe the disease will be. Members of the same family who have the same mutation may have very different symptoms.
Negative: The test did not find a mutation in the child's NF1 gene
A negative test result means a mutation was not found in your child's NF1 gene.
A negative test result does not rule out NF1. About 5% of adults with a clinical diagnosis of NF1 still have negative DNA tests. So even with a negative test result, a child may still be treated for NF1 or assumed to have "probable NF1." However, a negative test result can help a doctor rule out NF1 if, as a child grows older, they continue to have very few clinical signs of NF1.
Genetic testing may improve in the future, or new genes may be discovered, and a child with a negative test result may be offered genetic testing again.
Inconclusive: The test results were neither positive nor negative
Sometimes, the result of the genetic test is hard to interpret. The NF1 gene shows a mutation, but it is unclear if the change actually causes NF1. Some mutations are harmless; these are called polymorphisms (say: paul-ee-MOR-fis-ems).
With an inconclusive test result, the doctor or genetic counsellor may need more information. They may request blood samples and clinical information from other members of your family to help them interpret your child's test results.
Advantages: Reasons why you might want to have a genetic test
- A genetic test can diagnose a young child who does not yet have all the clinical signs of NF1.
- Once a mutation is identified, other relatives who are at higher risk to have NF1 can also have testing.
- A test can be done on a pregnancy to see if NF1 exists.
- A positive genetic test result cannot predict how mild or severe NF1 will be in a given individual, and relatives with the same mutation may show different symptoms.
Limitations: Reasons why a genetic test may not always help
- A positive test result cannot predict how mild or severe problems of NF1 may be.
- A negative test result does not necessarily rule out a diagnosis of NF1.
- If the test is inconclusive, other family members may need to be tested.
Deciding if NF1 genetic testing is right for you and your family
Genetic testing for NF1 is not right for everyone. It also does not always provide clear results.
If you have questions about genetic testing, ask your doctor to refer you or your child to a genetic counsellor or medical geneticist. They can explain the tests. They can also help you decide if genetic testing is right for you and your family.