On 24th October 2021, Australia’s Health Minister, Greg Hunt, announced new funding for pre-implantation genetic testing. This funding came into effect on 1st November 2021 and benefits couples who are known to have an increased chance of having a child with a life-threatening condition.
The Minister’s announcement gave the name “Mackenzie’s Gift” to the program, after Mackenzie Casella who sadly died of such a condition, spinal muscular atrophy (SMA), before her first birthday. Mackenzie Casella’s parents had never heard of SMA before Mackenzie was born, and did not know they both carried a genetic mutation which could lead to their child being born with a serious genetic condition. They campaigned tirelessly to raise awareness of the disease, and the need for better access to testing for parents.
The Minister’s move is a response to Mackenzie’s Mission, a large-scale research project currently underway that is funded by the Australian Government’s Medical Research Future Fund. Mackenzie’s Mission is aimed at improving access to genetic screening for prospective parents.
This new funding for preimplantation genetic testing (also known as preimplantation genetic diagnosis) is designed to assist couples who have an increased chance of having a baby with life-limiting or life-threatening genetic conditions.
What is preimplantation genetic testing and how is it different to what is already on offer?
There are several types of genetic tests available prior to or during pregnancy. The type and timing of the test varies with the type of genetic condition of concern.
Non-invasive prenatal testing
The most well-known test is non-invasive prenatal testing (NIPT). This is a screening test done during pregnancy to check for an abnormal number of chromosomes in the foetus. DNA from the foetus that is circulating in the mother’s bloodstream can be examined via a sample of the mother’s blood. If a chromosome abnormality is found, a diagnosis can then be confirmed or ruled out via further testing such as amniocentesis.
Reproductive carrier screening
There is a separate category of genetic conditions in which the number of chromosomes is normal but there are errors in any of a number of genes. Blood samples taken from prospective parents are analysed to look for genetic mutations in the parents i.e. “carrier screening”, which could be passed on to their child. The parents may be unaffected, but their child could be born with a serious genetic condition such as SMA, cystic fibrosis or fragile X syndrome. Although reproductive carrier screening has been available for some years, the Mackenzie’s Mission project is looking at what the impact could be of offering a screening test for hundreds of different conditions.
The test is ideally offered in the planning stage, before a pregnancy begins, so that the couple have time to consider their options. Carrier screening can also be offered in the early stages of pregnancy.
For most conditions of concern, it is necessary to screen both parents. For example, SMA is due to the affected child having inherited two abnormal SMN1 genes, one from each parent. Each parent is a carrier of SMA i.e. has only one abnormal SMN1 gene (the other copy being normal) and is unaffected. If both parents are carriers for SMA, the chance of their baby getting two abnormal copies of the gene will be 1 in 4.
For other conditions, it is only necessary to screen the mother. If the mother is a carrier, she is likely to be unaffected, and yet each of her sons has a 1 in 2 chance of being affected.
Currently the Mackenzie’s Mission reproductive genetic carrier screen covers approximately 1,300 genes which are associated with around 750 conditions. There are more genes than conditions because some genetic conditions can be caused by changes in more than one gene.
Mackenzie’s Mission is a research study and is offering carrier screening to about 10,000 couples through selected healthcare providers. The Australian Department of Health is considering a proposal for Medicare funding of carrier screening for three common conditions, cystic fibrosis, spinal muscular atrophy and fragile X syndrome. A range of carrier screening tests for prospective parents are also available privately to anyone planning a pregnancy.
Preimplantation genetic testing
If a couple knows that they have a high chance of having a child affected by a severe disorder, they can plan their family armed with this knowledge. A couple may choose to conceive naturally and accept the chance; they may have further tests during pregnancy; they may choose other options such as using donor egg or sperm; they may decide to adopt a child; or they may conceive through IVF and have genetic testing at the earliest stage of pregnancy i.e. preimplantation genetic testing.
The advantage of conceiving through IVF is that preimplantation genetic diagnosis can be performed on embryos. This type of testing uses genetic material from an embryo which has been fertilised through IVF and is deemed viable to be implanted into the mother’s uterus to begin a pregnancy. Before implantation, the pathology lab can determine whether the embryo carries any of the genetic conditions for which the parents are carriers.
That is where the recently announced initiative, Mackenzie’s Gift, comes in. Pre-implantation genetic testing is now funded under Medicare for couples having a baby through IVF where one or both parents have a known genetic change that places a future child at risk of a genetic condition, chromosomal disorder or mitochondrial disease.
The test was already on offer for IVF parents, but with no Medicare rebate the test could cost $3,000 – $4,000 out of pocket. Mackenzie’s Gift reduces the financial barrier to accessing this specialised form of genetic testing. This allows couples who are carriers of one or more faulty genes to select embryos that are not affected by a genetic condition so they have the best chance of a healthy baby.
This access to specialised pathology testing has the capacity to help a lot of families: nearly 1 in 20 babies born in Australia is conceived through IVF.
Genetic tests such as these are complex. Part of the process is consultation with an appropriately qualified genetic counsellor or clinical geneticist. They can provide information to help the couple decide if testing is right for them, and to help them understand their results. The choice is theirs to make.