In 2017, Rachael and Jonathan Casella lost their seven-month-old daughter Mackenzie to spinal muscular atrophy (SMA) – a severe, incurable genetic condition.
In a $20 million project named in Mackenzie’s honour, the Medical Futures Research Fund is improving access to preconception screening for the altered genes carried by many Australians. These genes pose risks for deadly genetic syndromes in their children.
Carrier screening explained
Everyone has two copies of most genes – one from each parent. When a person has one copy of a faulty gene (a gene mutation) associated with a genetic condition and one normal copy, they won’t have that condition, but will be a ‘carrier’ of it.
A carrier can pass on faulty genes to their children. When both parents pass on the faulty gene associated with a genetic condition, their child will have two faulty genes and no healthy copy. Sadly, the child will have the genetic condition.
When both parents carrying a gene fault for the same condition have children, there is a 25 per cent chance (in each pregnancy) their child will inherit faulty copies from both parents.
X-linked conditions are another type of genetic condition included in Mackenzie’s Mission carrier screening. Women have two X chromosomes and men have one X and one Y. When there is a faulty gene on the X chromosome it can cause a genetic condition, with boys and men usually more severely affected than girls and women.
Carrier screening is used to see if a person is a carrier of a genetic condition that could be passed on to their children.
Why reproductive carrier screening?
When couples planning a family or in the early stages of pregnancy have carrier screening, it is called reproductive carrier screening. The tests look at whether the couple has an increased chance of having a child with a genetic condition.
Every couple should be aware that carrier screening for genetic conditions is available, says Professor Martin Delatycki, co-lead of the Mackenzie’s Mission project which is being administered by Australian Genomics.
Recessive and X-linked genetic conditions are a major cause of death and chronic illness in children. Carrier screening means couples can make informed choices according to their personal wishes and values.
“Screening can be done before a baby is conceived (preconception) or in early pregnancy,” Delatycki explains. “If a couple is found to have an increased chance of having a child with one of the conditions for which screening is done, they have a number of options to avoid having a child affected by that condition.”
“These include testing an established pregnancy or testing embryos created by IVF, a process known as preimplantation genetic diagnosis (PGD). For a small number of conditions, diagnosis will enable early treatment to improve a child’s health.”
Screening currently incurs out-of-pocket costs but will be free for couples participating in the Mackenzie’s Mission project.
Professor Delatycki says screening is possible for hundreds of genetic conditions. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) recommends that all couples be offered screening for at least cystic fibrosis, spinal muscular atrophy, fragile X syndrome and thalassaemia.
However, no test can guarantee that a child will not have a genetic condition, Delatycki says. “First, no test can screen for every gene fault. Further, many genetic conditions are not inherited from the parents’ DNA, but rather occur due to a new gene fault in the individual egg or sperm they came from.”
A mission for the future
The Mackenzie’s Mission project will screen 10,000 couples for carrier status of about 500 genetic conditions. “We expect about one in 100 couples tested will receive a result that means they have a one-in-four chance of having a child with one of the conditions for which screening is done,” Delatycki says
If steps are taken to avoid having a child with those conditions, the number of children born with a severe genetic condition would reduce significantly.
The project will study the psychosocial impact, health economics and ethical implications of delivering a national carrier screening program, and determine the best way to implement it.
It will start in Victoria, Western Australia and New South Wales, with couples expected to be able to participate from late 2019. It will commence in all other states and territories in late 2020 and is scheduled to be finalised at the end of 2021.