Options for having children
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Q. I was wanting to know how the natural birth is meant to happen? I have been looking and a few sites have said different things. Is it a 100% right the child will not have it if the test comes back as a clear for the baby or is there still a chance of having HD?
Lara, 26, Australia
A. Hi Lara,
Thanks for your email. I’m not sure whether I’ve properly understood your question at the start of the email Lara. If you mean going ahead with a pregnancy without any form of testing, this is indeed an option that many couples will choose. For some couples the thinking behind this is that HD is a late onset condition and there is also the hope for disease modifying treatments in the future. In addition some couples may not wish to go down the route of ending a pregnancy if the prenatal test result was unfavourable.
In terms of testing and the sites you have looked at, it’s difficult to know where the discrepancy may have arisen. One possibility is the difference between an exclusion test and a direct mutation test? These tests can be done either during a pregnancy (usually by a procedure called a chorionic villus biopsy (CVB) at around 11 weeks in pregnancy or as part of a procedure called preimplatation genetic diagnosis (PGD) which is similar to IVF.
An exclusion test is an option for couples where the individual at risk does not wish to know whether he or she carries the gene fault (i.e. he or she has not had a predictive test and is not showing signs of HD) but is choosing not to have a child at risk of HD. Effectively an exclusion test involves tracking markers close to the HD gene to see which grandparent’s copy of the HD gene has been passed on. The test tells you whether the baby is at close to 0% risk or the same 50% risk as the at-risk parent. It is accurate but there is a theoretical small chance (<1%) of the result being incorrect. This is because it is not a direct test looking at the gene itself.
The direct prenatal test looks to see whether the HD gene fault is present or absent (i.e. length of CAG repeat). Again, this is an accurate test and is an option where the parent knows his or her own status (otherwise a gene positive result in the baby would tell you that the parent too was gene positive). There is an excellent genetic service in Melbourne Lara and I would really encourage you to contact them. They will also be able to discuss all your options when thinking of starting a family. It can be useful to talk over with someone with specialist knowledge how you feel about the options available and the different pros and cons of each. As discussed before on HDYO, there is really no right or wrong answer here, just a path that is right for you and your partner. Please do get back in touch if this reply does not answer your main question or you would like help in contacting the genetics dept.
All the best,