2018 ISPD Conference

Prenatal diagnosis for single gene disorders in Victoria, Australia, 1977-2015
Alice Poulton1, Jane Halliday1, Sharon Lewis2, David Amor3, Lisa Hui4

1Murdoch Childrens Research Institute, Parkville, VIC, Australia
2Murdoch Childrens Research Institute, Parkville, Victoria, Australia
3Murdoch Children's Research Institute, Parkville, Australia
4Murdoch Childrens Research Institute, Heidelberg, VIC, Australia
Objectives
This study aimed to examine the historical and contemporary use of prenatal diagnosis (PnDx) for single gene disorders in the Australian state of Victoria (~70,000 annual births), over a 39 year period.  The type and scope of disorders for which PnDx has been done were described to reflect how such testing had changed with advances in genetic technology and knowledge of the human genome. The study also aimed to examine information on preimplantation genetic diagnosis (PGD) for single gene disorders. 
Methods
This population-based study included data held in a register of all women in Victoria who had PnDx from 1977-2015. Single gene disorders were categorised using a systematic hierarchical approach designed to reflect potential distinctive aspects of the PnDx decision-making process e.g. type of potential disability (physical or neurodevelopmental), severity, and age of onset of the disorder. Data on PGD for single gene disorders from the two clinics undertaking these tests in Victoria were categorised in the same way for comparison. Trend data were analysed using chi squared tests.
Results
There was an initial increase in PnDx for single gene disorders (χ2=19.18, p<0.001), steadying at ≈115 each year since the late 1990s. The scope of disorders has doubled (n=22 in 1993, n=45 in 2015). Most tests (68%) were for disorders that primarily impair physical ability, while disorders impairing cognitive ability comprised 21%. Adult onset conditions (3%) and disorders lethal in infancy (2%) were proportionately low. 5% were unable to be categorised. PGD for single gene disorders has seen rapid growth with approximately 25% done for adult onset conditions.
Conclusions
PnDx for single gene disorders is performed in about 1 in 500 pregnancies, with no observable changes since PGD and carrier screening became available during the past decade. Testing for adult onset disorders is not common during pregnancy, but appears to be more acceptable in the assisted reproduction setting. Advancing technologies in fetal genomic sequencing will lead to further shifts in testing for single gene disorders, however the direction of change is unknown. Understanding and reporting trends and changes can contribute to planning future service delivery, providing an overview of interest in and scope of single gene testing to date.