A discovery by Hong Kong scientists may open up approaches to treating infertility and creating a new form of contraception.
Researchers at the University of Hong Kong have pinpointed a molecule that helps to bind the egg and sperm during fertilisation.
The sugar chain molecule called SLeX is found on the coating of the human egg, which binds to an incoming sperm like a lock and key. This enables the sperm to enter the egg to initiate fertilisation.
'When couples have trouble with fertility, we can now check if it's because of a lack of SLeX on the egg,' said Professor William Yeung Shu-biu, an obstetrics and gynaecology professor who collaborated with experts from Imperial College London, the University of Missouri and Academia Sinica in Taiwan.
The study was published in the latest issue of Science.
Over three years, researchers collected 195 unfertilised eggs donated by patients who sought help from Queen Mary Hospital's assisted reproduction programme. These eggs had undergone failed assisted reproduction procedures and were non-living.
They found SLeX on 70 per cent of the egg's surface. If the molecule's structure was altered, fewer sperm would bind to the egg.
They also discovered that when the egg was surrounded by a layer of SLeX antibodies, the binding of sperm and eggs would be suppressed by 70 to 80 per cent.
Egg fertilisation is divided into three steps - the sperm has to go through the coating of the egg, it undergoes a chemical reaction and loses it tail, before fusion between the sperm and the egg.
There are two main methods in assisted reproduction. The first one is intrauterine insemination or IUI, where the sperm swims towards the egg after being injected into the womb; the second is in vitro fertilisation, or IVF, where an egg is taken out of the body and sperm is injected directly into the egg, skipping the first step of fertilisation. The fertilised egg is then put back into the womb.
Yeung said while there was not yet evidence that the lack of SLeX was the cause of infertility, their discovery might allow doctors to determine affected men earlier.
'In the future, when doctors discover a problem with SLeX receptors on sperm, they can refer that patient directly to IVF and skip IUI,' he said.
Researchers expect the discovery to be put into clinical use in two years.
The same principle could be applied to contraception, he said. When the function of SLeX was inhibited, it could suppress the sperm from binding to the egg by 70 to 80 per cent. But more work needed to be done to get a 100 per cent blockage.
The number of assisted reproduction procedures at Queen Mary Hospital last year. About 40 per cent of them were IVF