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Genetic carrier screening: What GPs need to know

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Around one in 200 babies is born with an inherited rare condition.
 
These conditions account for 20% of infant mortality. And while they are individually rare, people on average are carriers of two severe autosomal recessive conditions.
 
While genetic carrier screening has traditionally only been offered to those with a family history and partners of identified carriers, as well as those of a particular ethnicity, that has since changed. 
 
National guidelines now recommend all women or couples planning a family, or who are in the first trimester of pregnancy, be given the option in order to understand their risk.
 
To help raise awareness among GPs and other healthcare professionals, the RACGP has launched the Beware the Rare education campaign.
 
Professor Jon Emery is a GP and adviser for the campaign. He says the earlier carrier screening is carried out, the better.
 
‘This provides couples an opportunity to plan their reproductive choices more into the future,’ he told newsGP.
 
‘Part of this campaign is around raising these issues when couples are beginning to plan a pregnancy, so preconception, because the reproductive choices are somewhat greater at that point.
 
‘But, of course, we know a lot of people will often get pregnant without them necessarily formally planning it, and so the other time to be having these discussions is early on in the first trimester of the pregnancy, and offering the couple the opportunity to consider whether they want to have carrier screening to see if they’re at risk of having an affected child.’
 
Modes of testing including either a mouth swab or blood test.
 
There are currently three types of carrier screening panels available: 

• Single-condition screening – for one specific inherited disorder
• Three-condition screening – for three of the most common inherited rare diseases (cystic fibrosis, spinal muscular atrophy, fragile X syndrome)
• Expanded carrier screening – for hundreds of different inherited disorders regardless of ethnic background or family history

According to Professor Emery, it is important patients referred for the expanded panel be aware that more genes being screened increases the likelihood of discovering an abnormality.
 
‘It’s increasingly likely of course [that] if you look for a thousand genes, most of us will carry one or two of those variances,’ he said.
 
‘[But] the odds of them actually having a child with somebody else who happens to have the same gene are quite low.’
 
If referred during preconception, Professor Emery says the female can be screened first, as carrier status is more relevant for X-linked conditions. If she is found to be a carrier of an autosomal recessive condition, the male partner can then be screened.
 
If both partners are found to carry the same gene, their likelihood of having an affected child is one in four.
 
It is recommended that all patients found to be carriers are referred on for genetic counselling to ensure they are supported in understanding their options.
 
‘In terms of preconception, there are a number of options,’ Professor Emery said.
 
‘From advances in genetic technology, which underpins some of the rationale for offering this as a preconception test, is something called pre-implantation genetic diagnosis.
 
‘This allows the couple using IVF technologies to genetically test the embryos before they’re implanted, so that the embryos that are being implanted are not affected.’
 
While Professor Emery acknowledges that genetic carrier screening can be a sensitive topic, he says it is an important discussion for GPs to have with their patients.
 
‘It can be difficult, particularly the preconception discussion, to know exactly when to raise that issue,’ he said.
 
‘But there are opportunities, particularly with women consulting, to bring up issues of whether they had thought about planning a family into the future and, if they’re in a long-term relationship, whether as a couple they would be interested in knowing their risk of having an affected child with one of these severe genetic conditions.’


Professor Jon Emery says the earlier carrier screening is carried out, the better.
 
Medicare does not currently provide rebates for most genetic tests, which cost patients hundreds of dollars.
 
A research program called Mackenzie’s Mission is setting out to change that, however, thanks in large part to Rachael Casella and her husband.
 
After losing their seven-month-old daughter Mackenzie in 2017 to spinal muscular atrophy type 1, a genetic neuromuscular disorder, the couple lobbied the Federal Government to make genetic testing routine and covered by Medicare.
 
In response, $20 million was committed from the Medical Research Future Fund to a three-year pilot study that will set out to screen 10,000 Australian couples for around 750 genetic conditions.
 
‘The expanded panel test costs between $600 and $900. So it’s not a cheap test,’ Professor Emery said.
 
‘Mackenzie’s Mission will hopefully provide new evidence around the accessibility of this test, and inform future decisions around whether these tests eventually become available through the Federal Government.
 
‘But I think we are increasingly going to see a greater role for genomic tests, both in terms of reproductive choices, but also in terms of predicting the way we respond to drugs and predicting our risks of a range of common diseases so that we can tailor our prevention more.’
 
The RACGP is hosting a free webinar, ‘Fertility, pregnancy and genetic testing options’, on Wednesday 5 August, 7.00pm–8.00 pm (AEST). The event attracts two CPD points. Visit the RACGP website to register.
 
GPs can access information and resources on genetic carrier screening through the RACGP’s education campaign website. There is also an accredited training module worth two CPD points.
 
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genetic carrier screening preconception pregnancy reproductive choice

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