Prenatal Testing

Prenatal testing is one of a range of options which may be of interest to couples who are at risk of passing the disease-causing version of the HD gene to a child. Testing options may vary from centre to centre, and may include amniocentesis and/or CVS. A genetic counsellor can help individuals and couples identify which option is most suitable to their circumstances and perspective. The purpose of prenatal testing is to determine whether a fetus has the HD gene. This information can be used by the parents to make an informed decision about whether to continue the pregnancy.

Points to consider

It is important to understand that prenatal testing involves considering the possibility of termination of the pregnancy if the fetus is found to have the HD mutation. Thus, it is a good idea to think very carefully about prenatal testing for HD and how you feel about pregnancy termination, well in advance of a pregnancy. You may wish to consider alternative reproductive techniques, such as donor insemination, or in vitro fertilization (IVF) with preimplantation genetic diagnosis may enable you to have a child, without the risk of passing on the HD mutation.

Once a pregnancy has occurred, there is very little time in which to absorb the information about the prenatal test and to make such important decisions. Where prenatal testing is positive for the HD mutation and the pregnancy is continued, there are potential difficulties of having a child identified from birth as one who has the HD mutation and who will develop HD later in life.

Ideally, all aspects and implications of prenatal testing for HD should be discussed with a genetic counsellor prior to a pregnancy, in order that the future parents and the counsellor have sufficient time to address all the important technical and emotional issues involved.

There are three different situations in which prenatal testing for HD may be done:

Definitive Prenatal Testing

1) The expectant parent has HD. This type of testing is called definitive prenatal testing, because the status of the parent with respect to HD is definite. For example, imagine Mary is pregnant and her husband John has HD. What needs to be determined is whether the fetus has inherited the disease-causing version of the HD gene from John. John’s DNA has been analyzed and it is known that he has inherited genes with 20 and 50 repeats. If the fetus inherited the gene with the 20 repeats, it has not inherited the HD gene alteration. If the fetus inherited the gene with the 50 repeats, then it has inherited the DNA mutation underlying HD.

2) The expectant parent has had predictive testing and has been shown to have inherited the gene mutation which causes HD. This is also considered definitive testing since the status of the parent is known (i.e. he or he or she has inherited the HD gene mutation, although symptoms of the disease are not yet present). Testing is done as described above, except that John is not yet affected with HD, although he has the gene. The outcome is also similar — the fetus has inherited from John either the gene with 20 repeats (not the HD gene) or the gene with 50 repeats (the HD-causing gene).

Exclusion Prenatal Testing

3) The expectant parent has no symptoms of HD, and does not wish to have predictive testing for herself/ himself. This type of testing is called exclusion prenatal testing, and is performed only under very rare circumstances. Additional information on exclusion prenatal testing may be obtained from a genetics centre.

HD Resources

There are many other online websites and resources which provide information regarding HD in general, support groups in your area, research updates and opportunities to be involved in clinical trials.

Our Stories

We understand that learning that someone in your family has HD can be devastating. It can leave you with questions, concerns, and no idea where to turn next. Find about more about what others have done in your situation – you are not alone.

Family and Friends

Finding out that your loved one has HD, or may develop it in the future is incredibly hard. You may feel concern, shock and anxiety but at the same time want to help and support your loved one.
Learning more about the condition and the testing process can help you understand and prepare for what HD means for both of you now and in the future.