Genetic testing

The fault in our genes

Genetic carrier screening can help couples understand and prepare for the risk of passing on an inherited condition

WORDS SARAH MARINOS

About one in 20 Australians carries a gene change or a faulty gene that increases the risk of their children being born with cystic fibrosis, fragile X syndrome or spinal muscular atrophy. Everyone carries several gene changes and if their partner is a carrier of a change in the same gene, that can lead to a child having a genetic disorder.

Traditionally, genetic carrier screening is offered to people with a family history of these conditions and their partners because, if both people carry the same gene change or fault, each of their children has a one-in-four chance of being born with that condition.

National guidelines now recommend all couples planning a family are told about genetic carrier screening so they can understand their risk of passing on an inherited condition.

Increasing awareness

“Most couples don’t know this screening exists, or they don’t think about it,” says Professor Martin Delatycki, clinical director at the Murdoch Children’s Research Institute’s Victorian Clinical Genetics Services.

“Most births are still to couples who have not been offered genetic carrier screening, and the vast majority of babies born with one of these genetic conditions are born into families with no known history of the condition,” he says.

What is genetic carrier screening?

Genetic screening tests certain genes to see if parents carry a faulty gene — if they do, there’s a one-in-four chance each of their children will have the condition. If the woman is a carrier of an X-linked condition, such as fragile X syndrome, there is up to a 50 per cent chance her sons will be born with the condition. There is also a chance of daughters being born with this condition, which is the most common inherited cause of intellectual disability.

Genetic carrier screening can look for cystic fibrosis, spinal muscular atrophy and fragile X syndrome, or expanded carrier screening tests check for hundreds of conditions. Tests require a blood or saliva sample and typically cost about $400, or $750 for expanded carrier screening.

The right advice

If a person is a carrier of a genetic condition, genetic counselling helps them decide what to do next.

“A couple can use IVF so they can test embryos and choose not to implant an embryo with that genetic condition,” says Wendy Burton, of the Royal Australian College of General Practitioners.

“Or a couple can go ahead with pregnancy and have their unborn child tested during pregnancy to prepare for a condition if their child has it. Some couples don’t want to know either way,” Dr Burton says.

Matter of choice

Increasing awareness of genetic carrier screening is about allowing couples to make an informed choice, Dr Burton says.

“People are aware that testing is available for conditions like Down syndrome and they’re aware of routine ultrasound scans to look for growth and congenital abnormalities. With genetic carrier screening, they can get a heads-up before a baby is conceived,” she says.

But it is important to consider the implications of screening before going ahead. If you find out you are at increased chance of having a child with a certain condition, will that change your plans?

“Think through the worstcase scenario: ‘If we are both carriers what would we do? Would we go down the path of IVF or testing pregnancies?’ If couples wouldn’t change anything, they may choose not to screen,” Prof Delatycki says.

“But if you would do something, that’s a good reason to do genetic testing.”

First person

SOON AFTER TESSA WATERHOUSE’S SON, NED, WAS BORN, HE WAS DIAGNOSED WITH CYSTIC FIBROSIS. SO

WHEN THE 43-YEAROLD DECIDED TO EXPAND HER FAMILY, SHE USED GENETIC CARRIER SCREENING.

“When I had Ned 15 years ago, I didn’t have any screening because I didn’t know it was an option. My first husband and I were both carriers of cystic fibrosis (CF), but we didn’t know — there was no family history.

“Ned was very sick when he was born and we were told he had cystic fibrosis ... Around that time, I discovered I was pregnant again, too, although it wasn’t planned.

“The chances of our second son, Lucas, having CF was one in four, so early in the pregnancy I had a test ... I was very distressed because I didn’t know how I’d look after two sick babies but, thankfully, Lucas didn’t have CF.

“When my second husband, Simon, 43, and I decided to have a child he had a genetic carrier screening test to find out if he was a carrier of CF. He isn’t and our son, Harvey, is a healthy four-year-old.

“Ned’s health has got better but if I’d known the risks of him having CF before he was born, I could have prepared myself for caring for a baby with complications.”