About reproductive genetic carrier screening
The information provided below is general information about reproductive genetic carrier screening. For information specifically about the genetic carrier screening that is provided through the Mackenzie’s Mission study, click here.
Reproductive genetic carrier screening is a test that looks at an individual or a couple’s genetic information, to find out if they have an increased chance of having a child with a genetic condition.
Genetic carrier screening does not test for all types of genetic conditions. This is explained further below.
A genetic condition is a problem with health and/or development caused by faults in a person’s genes.
There are thousands of different genetic conditions. These conditions can vary in severity from mild to seriously debilitating, including some that are life-limiting. Genetic conditions also range from being extremely rare to more common. Symptoms of some conditions are present at birth, others arise in childhood or adolescence, and some don’t appear until adulthood.
Individually, genetic conditions are rare; however, when considered together they are common.
Reproductive genetic carrier screening generally tests for serious genetic conditions that occur in childhood and have a significant impact on lifespan and/or quality of life. For some genetic conditions, early diagnosis and treatment can improve the child’s health.
A few examples of these conditions are cystic fibrosis (CF), spinal muscular atrophy (SMA) and fragile X syndrome (FXS). These three conditions are among the most common severe genetic conditions in childhood.
- 1 in 20 people carry a faulty gene for either SMA, CF, or FXS
It is important to note that reproductive genetic carrier screening does not test for chromosomal conditions, such as Down syndrome. Chromosomal conditions are caused by extra or missing copies/parts of a baby’s chromosomes, not by inheriting faulty genes.
For information on the genetic conditions that are screened for in the Mackenzie’s Mission study, click here.
Everyone has two copies of most genes – one from each parent.
A person is a ‘genetic carrier’ for a condition when they have inherited one copy of a faulty gene (sometimes called a gene mutation) linked to a genetic condition, but their other copy of the gene works normally. Genetic carriers usually won’t be affected by the genetic condition.
On average, everyone is a carrier of about two different faulty genes linked to genetic conditions, usually without ever realising it.
A genetic carrier can pass on his or her faulty gene(s) to their children.
For most of the genetic conditions included in reproductive genetic carrier screening, a child will only be affected if both parents carry the same faulty gene. This is known as an autosomal recessive condition, and is explained below.
In some cases, only the mother needs to be a carrier of the faulty gene for a child to have the condition. This is known as an X-linked condition, and is explained further below.
When the same faulty gene linked to a genetic condition is passed on to a child by each parent, the child inherits two faulty genes and no working copy. Therefore, the child will have the genetic condition.
When two people who carry the same faulty gene conceive a child, there is a 1 in 4 (25%) chance that their child will inherit a faulty copy of the gene from both parents and will have the genetic condition. This is the case for each pregnancy.
Cystic fibrosis and spinal muscular atrophy are examples of autosomal recessive conditions.
For more information about autosomal recessive inheritance, please see this fact sheet (PDF, 1 MB).
Image shared with the permission of the Genetic Support Foundation.
Females have two X chromosomes, and males have one X and one Y chromosome. If there is a faulty gene on the X chromosome, it can cause a genetic condition.
Usually males are more severely affected by X-linked conditions than females, because they only have one X chromosome. Females may be healthy genetic carriers who don’t show any signs of the condition, because they have a second working copy of the gene.
When a woman who carries a faulty gene on the X chromosome has children, there is a 1 in 2 (50%) chance of a male child having the genetic condition, and a 1 in 2 (50%) chance of a female child being a genetic carrier for the condition. This is the case for each pregnancy.
Duchenne muscular dystrophy is an example of an X-linked condition.
For more information about X-linked inheritance, please see this fact sheet (PDF, 704 KB).
Image shared with the permission of the Genetic Support Foundation.
Autosomal recessive and X-linked genetic conditions can have a significant impact on lifespan and/or quality of life in children.
It is estimated that more than one million people in Australia are affected directly or indirectly by a genetic condition.
It is important for people planning a family, or in the early stages of pregnancy to make informed choices according to their own personal wishes and values about having reproductive genetic carrier screening.
Previously, only people with a family history of a genetic condition, or those in population groups where particular genetic conditions are more common, were offered reproductive genetic carrier screening.
However, research shows almost all children born with a genetic condition have no family history of it. Therefore most people with an increased chance of having a child with a genetic condition are unaware of this.
It is recommended that doctors offer information about reproductive genetic carrier screening to all prospective parents. Having screening is a choice, and it is up to the couple to decide whether screening is appropriate for them.
Like all tests, there are limitations.
Reproductive genetic carrier screening will identify most people who are genetic carriers for any of the conditions screened, however there is always a small chance that a person who is a genetic carrier may not be identified.
Due to limitations with technology, the accuracy of reproductive genetic carrier screening varies depending on the condition. For some conditions, it is easier to identify genetic carriers through screening, whereas for others it is more difficult.
The term screening is used because not all the genes in a person’s DNA are screened, not all genetic conditions are covered, and not all faults in the genes screened can be identified by the testing technology. A ‘low chance’ or ‘negative’ result means the chance that a person or couple will have a child with any of the genetic conditions screened is low, but does not completely rule out the possibility.
There is still a small chance of having an affected child even after a low chance or negative result from reproductive genetic carrier screening.
No, this is a different test.
The non-invasive prenatal test (NIPT) and first trimester combined screening (FTCS) look at the baby’s chromosomes to detect chromosomal conditions, such as Down syndrome. Chromosomal conditions are different to the genetic conditions screened for in reproductive genetic carrier screening.
It is recommended that women in early pregnancy are offered screening for chromosomal conditions through NIPT or FTCS, as well as reproductive genetic carrier screening.
Yes. Reproductive genetic carrier screening for multiple conditions is available in many countries. Some screening is government-funded and some is user-pays.
Many countries also have reproductive genetic carrier screening programs in place for recessive conditions that are more common in their population.
In Australia, genetic carrier screening for thalassaemia, a genetic blood disorder, is government-funded. Screening for other conditions including cystic fibrosis, spinal muscular atrophy and fragile X syndrome are available on a user-pays basis. Click here to see the reproductive genetic carrier screening options available in Australia.