Scientists studying mice have identified a gene which could boost human fertility.
Experts say the discovery, announced in a journal today, could help people struggling to conceive naturally.
A Durham University team working with scientists from Osaka University in Japan were studying fertility in mice when they discovered that the gene, which makes a protein called PDILT, enables sperm to bind to an egg, a process essential to fertilisation.
They found that when the gene was switched off in male mice, less than 3% of females' eggs were fertilised compared to more than 80% in mice when the gene was left switched on.
It is the first time that a gene of this type has been linked to fertility.
Adam Benham, of Durham University's school of biological and biomedical sciences, said: "The protein is an essential part of the navigation system of sperm.
"It helps sperm swim through the oviduct to the egg and without it sperm get stuck.
"Our results show that navigating the oviduct is an important part of the fertilisation process.
"Like any navigation system, you have to programme where it is that you want to go and this protein plays an essential role in getting sperm to the right destination, in good shape, and in good time."
The researchers also found that the cumulus cells, a cluster of cells surrounding and protecting an egg, play an important role in fertility - their presence enables sperm to bind properly to an egg.
Although the research and findings are at an early stage, the researchers now hope to look at how the gene affects sperm-to-egg binding in humans.
The findings are published in the journal PNAS, Proceedings of the National Academy of Sciences.
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