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Mapping DNA of egg cells could boost IVF success

6 January 2014
Appeared in BioNews 736

Researchers in China have developed a new non-invasive method for detecting genetic defects in IVF embryos that could improve the chances of successful IVF for some patients.

At present, an IVF embryo at risk of genetic abnormalities can be sequenced before implantation, but this requires removing a cell from the dividing embryo, a process which can damage some embryos.

This new research, which studied 70 fertilised eggs from volunteer egg donors, uses a technique called MALBAC (Multiple Annealing and Looping Based Amplification Cycles) to sequence left-over fragments of cells from the early developing embryo, known as polar bodies. The polar bodies and egg pronucleus (the nucleus of the woman's egg during the process of fertilisation) together contain four copies of a woman's genes. The research team was able to show that the polar body sequences can be used to deduce the sequence of the egg pronucleus.

The team said that it could use this technique to check simultaneously for large chromosomal abnormalities that cause miscarriages, as well as for disease-causing genes in the mother's DNA, explains Nature News.

Co-author, Professor Xiaoliang Sunney Xie, from Harvard University, USA but who conducted the research with a team at Peking University, China said: 'With past methods we had too many holes in our sequencing and couldn't get a precise enough read-out to detect both big chromosomal abnormalities and tiny sequence changes [in the polar bodies]'.

The new approach cannot provide information about any genetic defects passed down by the father but more than 70 percent of chromosome abnormalities, the most common cause of miscarriage in older woman undergoing IVF, occur in the egg, reports the New Scientist.

Lead researcher, Dr Jie Qiao of Third Hospital, Peking University, said: 'Theoretically, if this works perfectly, we will be able to double the success rate of [IVF] technology from 30 percent to 60 percent or even more'.

Dr Yacoub Khalaf, consultant in reproductive medicine and surgery at the Assisted Conception Unit at Guy's Hospital, London, urged caution: 'The area of screening is appealing in theory but in practice has not delivered.

'If screening eggs or screening embryos is not robust and reliable it could cost women their eggs or their embryos, both of which are precious and finite'.

Dr Qiao said that the work will not immediately make it possible for couples to create 'designer babies' by selecting eggs with desirable qualities. 'The long-term safety of this technology remains to be further evaluated', she said in Nature News.

But Dr Edison Liu, president and chief executive of the Jackson Laboratory in Bar Harbor, Maine, USA said that 'IVF is becoming more common' and if the genetic selection of eggs and sperm could be done before fertilisation, 'it is conceivable that over time, the offspring of millions of selective IVFs will alter the genetic landscape of our species'.

The team has begun a clinical trial in China of polar body whole genome sequencing with 30 women with genetic disorders. 'We hope to have healthy MALBAC babies in 2014', said Professor Xie.

The research is published in the journal Cell.

Genetic test screens embryo without disturbing it
New Scientist |  20 December 2013
Genome Analyses of Single Human Oocytes
Cell |  19 December 2013
IVF success rate 'could be doubled'
BBC News |  20 December 2013
Non-invasive method devised to sequence DNA of human eggs
Nature News |  19 December 2013
14 November 2016 - by Dr Katie Howe 
US researchers have created functional eggs using DNA from small cells that normally form as waste products during egg development...
25 January 2016 - by Dr Nicola Davis 
Chinese researchers have identified genetic mutations that cause infertility in a small number of women...
16 March 2015 - by Dr Katie Howe 
A team of Spanish researchers has developed a test that could improve IVF success rates by identifying the optimal timing for embryo transfer....
24 March 2014 - by Simon Hazelwood-Smith 
A study has found that women who produce fewer eggs during IVF treatment may have an increased risk of miscarriage....
2 December 2013 - by Rebecca Carr 
Time-lapse imaging has been used to track the way that cells organise themselves to form an early mouse embryo...
21 October 2013 - by Dr Rachel Montgomery 
An IVF method that claims to be cheaper and safer than conventional methods may give older women a greater chance of pregnancy, according to a study...
8 July 2013 - by Siobhan Chan 
A 'powerful' form of genome analysis could improve embryo selection for IVF, according to scientists who report that the first baby has been born from this method...
20 May 2013 - by Emma Stoye 
A technique for monitoring embryo health could increase the chance of IVF couples having a healthy baby, according to a study from researchers at a private fertility clinic...
Comment ( - 04/02/2014)
High quality embryo are selected for transfer into mothers uterus. All chromosomal abnormalities are removed before transferring. Hence the outcome is best. These in turn increases the success rate of IVF. Latest IVF Laboratory equipments enables embryologist to perform to their optimum level.
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