The decision to have children can be huge in anyone’s life. Everyone has to decide for themselves whether they want to have children or not. Some people at risk of HD or who have the changed HD gene decide they want to have children, as this is part of a normal life and they’re prepared to take the risk. Most hope that by the time their children grow up there will either be a cure for HD, or better drugs to manage the symptoms. Others decide not to have children because they don’t want to burden their children with the risk of HD.
If you are at risk of HD or you carry the changed gene for HD and you wish to have children, there may be additional areas for you to consider. The two main concerns most people have are that:
- You may pass on the risk of developing HD to your children, and
- You may be anxious that you will develop HD and your children will experience living with a parent who has the illness.
There are many people who are available for you to talk to regarding your decision about having children. These people may include your partner, family, friends or professionals. If you think you might want to make use of prenatal testing options it is recommended that you meet with a genetic counsellor and clinical geneticist who can provide information about these options and arrange testing if this is what you decide.
If you are at 50% risk of having the changed gene, then your children are at 25% risk of having the changed gene. This means they have a 1 in 4 chance of having the changed gene for HD.
If you find that you have the changed gene, your children are at 50% risk of also having the gene and developing HD in the future. This means they have a 1 in 2 chance of having the changed gene.
There are a number of options available to reduce the risks of having an at risk child. These include:
- Prenatal Testing
- Exclusion Testing
- Preimplantation Genetic Diagnosis (PGD)
- Gamete Donation
- Adoption - adoption is not an option as adoption agencies will not approve a prospective adoptive parent if there is a known risk, i.e. a 50% chance that the parent will become unwell.
If there is time, early in the pregnancy the at risk person has the option of having a predictive test. If the result is normal there will be no need for prenatal testing. If the at risk person is found to carry the changed gene and has the intention to terminate the pregnancy if the foetus also has inherited the changed gene, prenatal testing can be performed. Prenatal testing involves testing a foetus in the early stages of pregnancy to see if it has the changed gene for HD. There are two methods used to do this: at different stages of the pregnancy - chorionic villus sampling (performed at 11-12 weeks) and amniocentesis (performed at 15-18 weeks). With both these methods there is a small risk (about 1%) that the procedure will cause a miscarriage.
If the at risk parent does not wish to have predictive testing, or the pregnancy is too advanced to allow time for this option, it is important to be aware that a prenatal result which shows that the foetus has the changed gene will automatically give this result to the at risk parent. It is therefore important to have the opportunity for discussion and preparation for this outcome through genetic counselling.
Prenatal testing is only offered by a genetics service for couples who wish to avoid passing on the changed gene to their child. This means that the parents of the foetus will have the intention of terminating the pregnancy if the prenatal test reveals that the foetus carries the changed gene. This is a very emotional, challenging and difficult decision to make, and therefore requires a lot of discussion and consideration of all of the options. If the pregnancy is continued the prenatal result will become a predictive result for the child who will then be denied the opportunity to make the decision about testing for themselves as an adult. It is well established that only 25% of people at risk decide to be tested. This situation is also likely to create considerable anxiety within the family and may also lead to discrimination against the child in various areas, such as insurance.
Exclusion testing tends to be used when a person is unsure about their status and wants to remain at 50% risk. It involves taking blood samples from three generations of your family – you, your foetus and your affected parent. This can be a problem as you may have lost contact with your parent, or your parent may be deceased. The test tells you if you and the foetus have inherited the same chromosome 4 from your affected parent. It will not tell you whether the gene on this chromosome is the changed gene for HD, or if it is the normal gene.
A major disadvantage of Exclusion Testing is that there is a risk of terminating a healthy foetus.
Two options are available for PGD.
1. If the at risk partner has had a predictive test and is known to carry the changed gene.
This procedure uses In-Vitro Fertilisation (IVF) to fertilise a woman’s eggs with her partner’s sperm in a laboratory. The embryos are then tested for the changed HD gene. Only embryos that do not have the changed gene are implanted into the womb. This means the baby will be born with no risk of developing HD. Any remaining unaffected embryos can be stored for later use as required. However, like all IVF procedures the success rate is quite low (1 in 5) and can be a lengthy and emotional process. The financial cost is also quite high.
2. If the at risk partner does not wish to have a predictive test and is therefore at 50% risk.
In this instance, instead of testing directly for the changed gene, exclusion testing can be performed using PGD. This approach involves taking blood samples from three generations of your family – you and your partner, your foetus and your affected parent. This can be a problem as you may have lost contact with your parent, or your parent may be deceased. The test tells you if you and the foetus have inherited the same chromosome 4 from your affected parent. It will not tell you whether the gene on this chromosome is the changed gene for HD, or if it is the normal gene. The disadvantage of exclusion testing is that there is a 50% chance that the excluded embryos will not carry the changed gene.
This method uses a donated egg or sperm in place of the affected or at risk parent. For more information please contact The National Gamete Donation Trust. They can provide a list of all clinics in Australia that treat people with donated eggs or sperm, and lists of all clinics aiming to recruit egg or sperm donors.
Adoption is not an option as adoption agencies will not approve a prospective adoptive parent if there is a known risk, i.e. a 50% chance that the parent will become unwell.
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