15 November 2017

Where’s the line for routine genetic screening?

Clinical O&G

The Murdoch Children’s Research Institute is struggling to get its facts straight in its push for routine genetic screening for three inherited conditions.

Researchers have argued that genetic testing for carrier status of cystic fibrosis (CF), fragile X syndrome (FX), and spinal muscular atrophy (SMA) would be worthwhile because the number of pregnancies affected by these conditions combined is comparable with the Down syndrome birth rate.

The comparison was based on new data, published this month in the journal, Genetics in Medicine, from the first 12,000 individuals to be screened for these three genetic conditions in Victoria.

However, likening live births with Down syndrome to pregnancies affected by CF/SMA/FXS is like comparing apples with oranges, according to Associate Professor Lisa Hui.

Professor Hui is an academic obstetrician and gynaecologist at the University of Melbourne, and a spokesperson for The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG).

While the combined rate of CF/SMA/FXS was around 1 in 1000 pregnancies in this study, this was not similar to the rate of pregnancies affected by Down syndrome as the authors suggest, Professor Hui said. The most recent published data from Victoria showed the actual rate of Down syndrome in 2015 was 1 in 360 pregnancies.

The difference was due to the higher rate of miscarriage and stillbirth for pregnancies affected by Down syndrome, as well as post-screening terminations, Professor Hui said.

Professor David Amor, the senior author and a senior consulting specialist at Victorian Clinical Genetics Services (VCGS), conceded Professor Hui’s numbers were accurate. However, the rate of live births with Down syndrome, which is around one in every 1000, was similar to the combined rate of CF/SMA/FXS, he said. And live birth was the outcome that people were seeking to avoid through testing.

“When studying chromosome abnormalities, there is always the problem that the incidence starts high and decreases during pregnancy,” Professor Amor said.

However, RANZCOG remains on the fence about whether GPs should routinely recommend genetic carrier screening for these conditions.

From a public health perspective, Down syndrome and other chromosome conditions (including Edwards syndrome and Patau syndrome) remained a higher priority for now because they were more common, Professor Hui said.

Genetic carrier testing should be an informed, voluntary choice made by the woman, with adequate resources for post-test counselling and partner testing, she said.

Most people were not aware that screening was an option, and many health professionals did not know that 88% of carriers had no family history, study author Alison Archibald, an associate genetic counsellor with VCGS, said.

Screening for Down syndrome has been a government-funded, routine pregnancy test since the 1970s, whereas carrier screening for CF/SMA/FXS costs around $385 per person.

Ms Archibald and Mr Amor are both employees of VCGS, which is a not-for-profit provider of a range of genetic tests, including the “prepair” test, which was the subject of this study. However, they have no other financial relationships.

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Linda Mann
1 year 2 months ago
This comes hot on the heels of a letter to me ( and i would guess all NSW GPs) from Brad Hazzard MP, minister for Health in NSW, telling a sad tale of a child who died of SMA in the absence of prenatal screening. He tells me that NSW Health is updating the ” thinking of having a baby ” consumer brochure to include info on screening for heritable diseases ( so rarely Down syndrome). He assures me ” this will support the information nd advice you ( me , the GP) provide to prospective parents”. Really? I have… Read more »