Mapping DNA of egg cells could boost IVF success

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.