When a couple cannot conceive naturally, they often turn to in-vitro fertilisation. And that’s when the spectre of ‘aneuploidy’ arises — the risk that a fertilised embryo will have an abnormal number of chromosomes instead of the usual 46, triggering a range of congenital disorders, most of which result in miscarriage, stillbirth or death of the baby soon after birth.
‘One of the greatest challenges for IVF clinics is identifying which embryos are suitable for transfer back into the mother,’ said Dr Kylie Dunning, chief investigator of reproductive success research at the CNBP. ‘Most aneuploidies are lethal, and the risk of aneuploidy increases as a woman ages.’
Even in natural conception, chromosome abnormalities are detected in 1 out of 160 live births, and account for some 35% of miscarriages. In some embryos, aneuploidy arises after fertilisation resulting in an embryo that is mosaic — one that contains both aneuploid and chromosomally normal cells. In IVF, the only way to determine if a fertilised embryo is free of aneuploidy is to do a biopsy by carefully drilling through the layer surrounding the membrane of a 5-day-old embryo and using a pipette to suck up 5 or 6 of the cells that go on to form the placenta. Then the DNA of the extracted cells is analysed.
Known as pre-implantation genetic screening, the technology can identify some 2000 inherited single gene disorders and was thought to be 98% accurate. Until recently.
‘Several studies are now showing that a biopsy is not as accurate at diagnosing how many cells in the embryo are aneuploid,’ said Dr Dunning. ‘If there’s no evidence of aneuploidy in the cells that go on to form the placenta, it doesn’t guarantee there’s no aneuploidy in the inner cell mass that develops into the baby.’
In addition, studies now show that mothers who are implanted with biopsied embryos that pass genetic screening are at increased risk of pre-eclampsia — a pregnancy disorder that leads to complications like impaired liver function, kidney dysfunction and fluid in the lungs, increasing risks for both mother and baby. ‘And it also predisposes the mother to a lifelong increased risk of cardiovascular disease,’ Dr Dunning added.
Working with colleagues at CNBP’s Early Development group, led by Prof Jeremy Thompson at the University of Adelaide, Dr Dunning is developing a non-invasive diagnostic technique with her PhD student, Tiffany Tan, that relies on scanning a whole embryo with low levels of light emitted from LEDs of differing wavelengths, then capturing the light that is emitted by the cells using a highly sensitive camera loaded atop a microscope.
‘It’s a camera normally used in astronomy to capture very low levels of light from stars,’ she said. ‘We’re able to see the autofluorescence reflected from the embryo in a dish culture, which allows us to measure what’s going on inside. We found that this is quite good at deciphering which embryos have a high number of cells that are aneuploid.’
Cellular organs, such as mitochondria and lysosomes, naturally emit autofluorescence when exposed to light. And the researchers have established that the higher the amount of aneuploidy in an embryo, the lower the autofluorescence from flavins, a substance that — when bound to proteins — helps mediate and accelerate chemical reactions.
Importantly, they have also shown that, in mice, the process causes no damage to embryos: ‘We’ve looked at whether it affects an embryo’s ability to complete pre-implantation development, and it doesn’t affect that. We’ve looked at whether it damages DNA, and it doesn’t,’ said Dr Dunning.
‘We’ve implanted both the imaged and non-imaged embryos into mice, and we’re now letting the mice deliver pups to show that we’re not inducing any sort of damage that’s going to affect the lifelong health of the mother or the offspring.’
The technique relies on sophisticated algorithms developed by CNBP’s University of New South Wales node in Sydney, which can automatically identify high-risk embryos that have a high amount of aneuploidy.
The goal is to do away with embryo biopsies, reducing risk and speeding up the process: ‘We don’t have to extract the DNA, then freeze the embryo and wait a few days for the genetic tests, then revive the embryo and transfer it,’ said Dr Dunning. ‘We could just take a picture of the embryo, see how much aneuploidy there is and transfer it into the mother the same day. That would be wonderful.’