A new type of in-pregnancy testing called Non-Invasive Prenatal Diagnosis (NIPD) is now available for families affected by the heritable (genetic) form of retinoblastoma. This article explains more about the process, the benefits it can provide, and who is eligible.
What is NIPD?
Non-invasive prenatal diagnosis (NIPD) uses a blood sample taken in pregnancy from the mother’s arm to look at the genetic make up of the baby. NIPD is different from invasive prenatal tests, such as chorionic villus sampling (CVS) and amniocentesis, that are associated with a small risk of miscarriage. NIPD does not pose any risk to the baby.
How is NIPD possible?
NIPD is possible as we know that some of the baby’s DNA from the placenta is circulating in the mother’s bloodstream during pregnancy. This is called cell free fetal DNA (cffDNA) and is detectable from about 4-5 weeks gestation. The amount of fetal DNA generally increases as the gestation of the pregnancy increases and disappears soon after the baby is born and so is specific to each pregnancy. The earliest NIPD can be undertaken is approximately eight weeks’ gestation as there is usually enough fetal DNA to be tested at this stage. Testing can be undertaken later into the pregnancy as the amount of fetal DNA continues to increase.
Who is this test for?
This test is for babies at risk of inheriting retinoblastoma. Babies are at risk if a parent or a sibling has the heritable (genetic) form of retinoblastoma. Testing is technically challenging because of the small amount of the baby’s DNA present in the blood sample compared to the amount of DNA from the mother. Depending on which family member is affected (mother, father or previous child) the type of test performed can vary, as well as whether the test is possible and what samples are required in order to perform the test. Therefore it is important to make enquiries either before becoming pregnant, or at the very earliest stages of pregnancy, if this is something you are likely to request.
For a mother affected with retinoblastoma:
- The mother must have a confirmed diagnosis of heritable retinoblastoma by genetic testing.
- The couple needs to have had a previous child (either affected or unaffected). This makes the test informative.
- DNA must be available from this child. A stored sample of DNA may be used.
- Blood samples are required from both parents of the baby.
- Testing can be performed anytime during pregnancy after eight weeks’ gestation.
- In twin/multiple pregnancies NIPD is not possible.
For a father affected with retinoblastoma:
- The father must have a confirmed diagnosis of heritable retinoblastoma by genetic testing.
- Blood samples are required from both parents of the baby.
- A blood sample from both parents must be received either pre-pregnancy or before 12 weeks’ pregnancy to check that the test is suitable for the family. Depending on the type of variant detected in the father, a sample from a child of the couple may be required as well.
- In twin/multiple pregnancies NIPD is not possible.
For families with a previous child affected with retinoblastoma:
- The child must have a confirmed diagnosis of heritable retinoblastoma by genetic testing.
- DNA must be available from this child. A stored sample of DNA may be used.
- The parents must be confirmed non-carriers by genetic testing.
- Blood samples are required from both parents of the baby.
- A blood sample from both parents and the affected child must be received pre-pregnancy or before 12 weeks pregnancy to check that the test is suitable for the family.
- In twin/multiple pregnancies NIPD is not possible.
What are the benefits of NIPD for families with retinoblastoma
Babies at risk of inheriting retinoblastoma are currently tested as soon as possible after birth, ideally on a blood sample taken from the umbilical cord, with the aim of a result within two weeks. A test result in pregnancy ensures there is no delay in diagnosis. When a baby is found to be unaffected, families are saved unnecessary worry during the pregnancy and around the time of birth.
When a baby is found to be affected, a result in pregnancy gives parents time to process the diagnosis before the baby’s arrival. Families know in advance they will need to travel with their newborn for screening at a national centre in the first few days after birth. This information is particularly helpful for families who live a long way from London or Birmingham, who otherwise would have their first eye examination at a local centre. If any tumours are detected at the first screen at a national centre, a management plan can be made and treatment commenced as early as possible. Retinoblastoma tumours can be present at birth and grow quickly. The earlier a tumour is detected, the more easily it can be treated.
It has not yet been established that earlier delivery is associated with better outcomes in retinoblastoma. However, some families may choose to use the outcome of the NIPD test in their decision making around delivery, for example in accepting or declining induction of labour if offered by their obstetric team for other reasons.
Invasive prenatal testing has been available previously but is not often chosen by parents due to the small risk of miscarriage (likely less than 0.5%, or 1 in 200) associated with this type of test. NIPD is non-invasive and is not associated with an increased risk of miscarriage. NIPD can also be undertaken earlier in pregnancy than invasive procedures. The blood sample can be taken at a local hospital by a midwife, or phlebotomist if required, as long as the test has been organised with the genetics team and laboratory.
How is NIPD done?
Depending on the type of test being performed, it may be necessary to provide samples before pregnancy, to check that the test is suitable for the family. Once it has been confirmed that testing in pregnancy will be possible, a dating scan at around eight to nine weeks’ gestation is required to confirm the gestation of the pregnancy and to ensure the pregnancy is not a twin or multiple pregnancy. If the gestation is eight weeks or more a blood sample can be taken for the test. If the pregnant woman is less than eight weeks’ gestation, arrangements will be made to take the blood sample at the appropriate time.
The blood sample is taken from the pregnant mother’s arm just like any other blood test and sent to the laboratory. NIPD determines which copy of the retinoblastoma gene (RB1) the baby has inherited (the standard copy or the one with the gene change). It is therefore able to predict if the baby will be affected with retinoblastoma. The results may take up to 14 working days.
How accurate is the test?
Only a very small amount of the baby’s DNA is present in the mother’s blood. It is therefore possible that the laboratory is unable to detect the baby’s DNA and therefore may need to repeat the test by requesting an extra blood sample. In around 5% of cases the laboratory are unable to give a result despite repeated blood tests. The result would then be reported as inconclusive. If a result is possible, the accuracy of the test is very nearly 100%. There is a very small risk of misdiagnosis with the testing due to the technical process. It is estimated that between 1 in 500 to 1 in 1,000 people will receive an incorrect result.
Access to the testing
Individuals who would be interested in this test should contact their retinoblastoma service for an appointment with a member of the clinical genetics retinoblastoma team.
Example Families
Punam had retinoblastoma in both eyes as a child and has been told that she can pass this onto her children. She and her husband Jamal previously had a daughter Aysha, who was tested as a new-born and found to be unaffected. While they were very happy that Aysha did not have the disease, Punam and Jamal found the pregnancy very stressful, worrying about whether Aysha would be affected and what this would mean in terms of treatment. However they did not want to put the baby at risk with an invasive prenatal test. When Punam became pregnant again they requested NIPD. The test was performed at 12 weeks’ gestation and the baby was found to be unaffected. Punam and Jamal were delighted and enjoyed a stress-free second and third trimester.
Peter had retinoblastoma in one eye as a child. Genetic testing determined that it was the heritable form of the disease. Peter is now thinking of starting a family with his partner Katherine. They asked to be referred for NIPD and provided blood samples. Analysis of Peter and Katherine’s DNA showed that NIPD was available to them. When Katherine became pregnant, a second blood sample from her was sent for testing at 20 weeks gestation. NIPD analysis showed that the baby would have retinoblastoma. While upset, Peter and Katherine were relieved to have time to come to terms with the diagnosis. Their clinical team also set up a detailed treatment plan so both Peter and Katherine would know what to expect when the baby was born.
When Mia was 2 years old, she was diagnosed with retinoblastoma. Although both her parents, Justyna and Tom had no history of the disease, it was found that Mia had the heritable form of retinoblastoma. Justyna and Tom decided they would like a second child and requested NIPD. DNA analysis showed that NIPD was available to the couple and the test was performed when Justyna was 14 weeks pregnant. The results showed that the baby would not develop retinoblastoma.
FAQs
In time, do you expect this will replace taking cord bloods at birth for eligible families?
Patients undergoing NIPD are currently still having cord blood taken at birth to confirm the diagnosis. In families where NIPD is not possible or where a couple decide that they would rather not receive a result during a pregnancy, testing a sample of cord blood remains standard practice and a provisional plan for screening would be made in the event that the baby is found to carry the gene change.
Is this available free of cost, on the NHS, across the UK?
NIPD is currently only available on the NHS in England. We can offer testing to the whole of the UK, including the Republic of Ireland, but it would be a decision for the devolved nations as to how it was funded. If you are not based in England, contact your local clinical genetics centre in the first instance.
Why do you require a DNA sample from the father if it is the mother who is the carrier?
We require a DNA sample from the father as well as a previous child when we are testing for maternal inheritance. This is because our test is not sensitive enough to directly test the baby for the exact retinoblastoma gene (RB1) change when the mother is a carrier as well. Instead, we look at the whole RB1 gene and determine which copy has been inherited by the baby from their mother (the mother has two copies of the RB1 gene herself, one that carries the Rb gene change, one that doesn’t). To work this out we need DNA from a previous child and the father.
Why do you need a DNA sample from a previous child in cases where the mother has heritable retinoblastoma (Rb), but not where the father has heritable Rb?
When a father has heritable Rb but the mother does not, we usually look for the specific Rb variant in the mother’s blood. If we detect the variant, we know it must have come from the baby. When the mother has heritable Rb this type of test is not possible and we need to use a more sophisticated test. When testing for maternal inheritance of Rb, we determine which copy of the RB1 gene the baby has inherited from its mother. To do this we need a DNA sample from the father and a previous child.
Is there anything that would rule anyone out of being eligible?
This can be a bit complicated and will need discussion with your genetics consultant. However in general:
- NIPD is only offered for families with a known heritable RB1 gene change which has been confirmed through genetic testing.
- We cannot test twin/multiple pregnancies.
- We are not able test pregnancies where the parents are consanguineous when the mother has heritable Rb
- For a father affected with retinoblastoma, or for families with a previous child affected with retinoblastoma where the parents are not carriers, the type of RB1 gene change may affect whether we can offer the test.
If I chose not to have NIPD, will this affect my baby’s treatment if they do have Rb?
Some couples may not wish to test during the pregnancy as, should they find their baby has the gene change, they feel this would increase their anxiety for the remainder of the pregnancy, without being able to do anything until after the birth. In these cases, a provisional eye screening appointment can be made and cord blood taken at birth to check for the gene change. Results are returned in most cases in 7-10 days. If a gene change is not found, the screening can be cancelled. If the gene change is detected, the baby can attend their first screen as planned. Subsequent management is then based on the findings at the initial screen.
Glossary:
DNA is a chemical found in every cell, which carries genetic information. It has all the instructions that a living organism needs to grow, reproduce and function.
A variant is an alteration in the DNA genetic code. Some genetic variants cause disease
Gestation = the length of a pregnancy
Heritable: can be passed from parent to child (also referred to as genetic).
Invasive prenatal testing involves inserting a needle into the mother’s tummy, and carries a small risk of miscarriage
A phlebotomist is a person who is trained to take blood from a patient
Consanguineous: In clinical genetics, a consanguineous marriage is defined as a union between two individuals who are related as second cousins or closer.
Authors:
Dr Foster, Consultant in Clinical Genetics at Birmingham Women’s & Children’s Hospital NHS Foundation Trust
Dr Gerrish, R&D Scientist at Birmingham Women’s & Children’s Hospital NHS Foundation Trust
Dr Hay, Consultant in Clinical Genetics at Great Ormond Street Hospital