Episode 5: Screening for Genetic Conditions
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Episode 5 Content and Overview
In episode 5 of the Pregnancy and Childbirth podcast, Dr Greg discusses reproductive carrier screening.
Carrier screening involves testing parents prior to pregnancy, or in the early stages of pregnancy, to determine whether or not they are at risk of having a baby with a serious genetic condition.
It is recommended that all couples in Australia who are contemplating pregnancy, or who are in the early stages of pregnancy, are informed about their options in regard to reproductive carrier screening.
In this podcast you’ll discover how carrier screening works, what conditions we can test for and what your options are if your baby is found to be affected by any of these conditions.
Additional Resources
Mackenzie’s Mission will provide reproductive genetic carrier screening to 10,000 Australian couples who are either planning to have children or are in early pregnancy
Sonic Genetics gives doctors and patients access to an extensive range of genetic tests, provided through Sonic Healthcare’s network of Australian and international laboratories
NSW Health reproductive genetic carrier screening fact sheet
Transcription
0:01
Hi, I'm Greg Jenkins, and welcome to this edition of my pregnancy podcast. Today we're going to be talking about a thing called reproductive carrier screening. This is testing that can be carried out, either prior to pregnancy or during the early stages of pregnancy to determine whether you and your partner, may be a risk of giving birth to a child, who could have a potentially serious genetic condition. It is recommended that for all couples in Australia who are contemplating pregnancy, who or who are in the early stages of pregnancy, that they be informed about their options in regard to reproductive carrier screening. You may choose not to pursue testing in this area but it is important part of your decision making to be informed about this and to give it some consideration.
0:53
So before we can talk about reproductive carrier screening, we need to understand a little bit about what it is that we're talking about. So this is not about testing for conditions like Down Syndrome, for example, these are chromosome conditions rather than genetic conditions. So what we're talking about in this case, is conditions that would usually be inherited from the parents. And the way that these are inherited is that in most instances, one or both of the partners are a carrier for this condition, and they pass the condition on to some of their children. There are quite literally 1000s of these conditions. And it's estimated that there may be something like a million people living in Australia, who are affected by a genetically inherited condition.
1:44
Some of these conditions are very serious, and have a major impact on both duration and quality of life. And some relatively minor with minimal impact on quality of life. The commonest of these conditions is something that you might be familiar with, is a condition called Cystic Fibrosis. Now in order to understand how this works, we need to have a bit of a chat about genetics. So genes generally occur in pairs. In order to inherit a genetic condition, you generally need to have both pairs of the gene for that condition. Now, we all carry faulty genes, on average, most of us carry at least two faulty genes. Now, if you happen to be having a baby with somebody who has the same faulty gene as you, then there's a possibility that some of your children will get both of your faulty genes, and therefore will actually have the condition that's related to these genes, and this is called autosomal recessive inheritance. So these genes are recessive. And in order to get the disease, which the gene is particular to, you need to have both of the faulty genes.
3:01
There's another way of inheriting a genetic condition, and that's called an X linked recessive condition. In these conditions, the faulty gene resides on the X chromosome. Now, you're probably aware that females have 2x chromosomes and males have an X chromosome and a Y chromosome. So for an X linked condition provided there is a normal X chromosome to balance out the gene on the faulty X chromosome, the condition won't generally occur. However, in boys, if they inherit the X chromosome with the faulty gene, they don't have an extra another X chromosome with a normal gene to cancel it out. So in X linked conditions, we normally say the visible nature of this disease, are much more predominantly in boys than in girls. I mentioned that because in the most commonly performed test to look for reproductive carrier screening, it involves a combination of autosomal recessive conditions, and an X linked recessive condition also.
4:16
So what does it mean to be a carrier of one of these conditions? Well, usually it won't have any health implications at all. But for some conditions, it might mean that you have some mild features of the actual disease itself. But in most instances, it will have minimal implications to your health if you are a carrier of one of these conditions. The most commonly performed testing option available tests for three of the more common genetic conditions. These three conditions are cystic fibrosis, which occurs around about 1 in 3000 children born, spinal muscular atrophy, which occurs between 1 and 5000 and 1 in 10,000 children and fragile X syndrome, which occurs between 1 in 5000 and 1 in 10,000 children. So as you can see, even when we add these three conditions up, they don't occur particularly commonly, however, they are particularly important.
5:20
You might have heard of some publicity surrounding Mackenzie's mission. This is about a baby that was born with a condition spinal muscular atrophy. The baby died at around seven months of age, and her parents who unbeknown to them at the time were both carriers of this condition, decided that other parents should be educated and informed about the issues surrounding serious genetic conditions and the potential for passing these conditions on to the children.
5:58
So as I mentioned, the most common panel of tests that's available is a test to check for those three conditions. There are, however, what are called expanded carrier screening tests that test for quite literally hundreds of conditions. And it's quite possible that we'll see in the next few years government funding testing available, which will test for up to 700 to 1000 different genetic conditions. If you're interested in pursuing expanded carrier screening, then you should talk to your health care provider about how to access these options. Now, I should also mention that this testing can be done prior to pregnancy as well as during the early phases of pregnancy. And there is an excellent website. If you Google search, Mackenzie's mission, there's some very good information there about reproductive carrier screening, and some more detail about Mackenzie's mission itself.
7:01
The other thing to mention is that this test at the present time unless you're enrolled in a study is not accessible for Medicare rebate or Medicare funding. So it is reasonably expensive. The three panel tests looking at cystic fibrosis, spinal muscular atrophy, and fragile X is in the order of $350 per partner, the general process would be that the woman gets tested first and if she's found to be a carrier for one of these three conditions, then her partner would usually then undergo follow up testing.
7:41
So what if you decide to pursue this testing? And what if you're both found to be a carrier for the same condition? Say, for example, you're both carriers for cystic fibrosis, or you're both carriers for spinal muscular atrophy. This means that there's a likelihood that one in four of your children will actually have this condition. If you happen to be pregnant once the testing is done, and this information is now available to you during pregnancy, then further testing options would involve tests that that take a sample of the baby's cells so that the baby's genetics can be determined. So this would usually be either an amniocentesis, which involves putting a needle into your tummy and taking a sample of the amniotic fluid, or a test called a CBS, which also involves putting a needle into your tummy, and taking a sample of the baby's placenta. From these tests, it can be determined with quite a high degree of reliability, whether your baby actually has the condition or doesn't have the condition.
8:49
The third condition, which I mentioned is fragile X syndrome. If the mother happens to be a carrier for fragile X syndrome, and if the child is a boy, then there is a 50% chance that he will be affected by this condition. Now, if you determine that you are both carriers, and your baby is affected by the condition, and this has been confirmed with what we call invasive testing, then unfortunately, this condition cannot be rectified and your options would then relate to whether you wanted to continue with the pregnancy, or whether you chose to not continue with the pregnancy on the basis of the new information that you now have.
9:36
If you had these tests carried out before becoming pregnant, then there's another management option available. And that option would be to have IVF treatment and have your embryos tested for these conditions before the embryos are placed back into your uterus. So for couples who've had a baby with one of these conditions in the past whether it continued to full term or whether it didn't, many of these couples will choose to go down the pathway of having IVF and what's called pre-implantation genetic testing with future pregnancies.
10:15
So in summary, I know this is all a bit complicated. This testing is available to all couples who are thinking about having a baby or who are in early pregnancy. The commonest test that's done is the test to check for three genetic conditions. But there is testing available for a much wider panel, it is more expensive, but it is available. The majority of couples that I see don't tend to go down the pathway of undertaking this testing, but it definitely is available and it certainly can be facilitated if you're wanting to do it. The conditions that we're testing for are uncommon, but they are potentially very serious. And if you and or your partner were found to be carriers for these conditions, then further testing would be necessary in order to determine whether your baby was affected by this condition or not.
11:13
If you're interested in finding out more about genetic carrier screening, you should definitely talk to your health care provider. And if you're interested in pursuing testing, similarly, talk to your health care provider and this can be very easily arranged. I have included some links to additional resources in the show notes for this episode. Thanks for listening. I hope you found this episode informative and I would welcome any feedback or suggestions regarding future episodes. Bye for now.
