Gene found by NZ team has fertility clues

New Zealand scientists are trumpeting a medical breakthrough that may help infertile couples and produce a safer contraceptive.

The discovery by AgResearch of the gene responsible for producing twins and triplets in sheep may also improve farm productivity.

The discovery, made at the crown research institute's molecular biological unit at Otago University and Wallaceville, near Upper Hutt, comes days after the announcement that scientists have cracked the human genetic code.

The scientists, led by Dr Sue Galloway and Dr Ken McNatty, discovered that mutations in a specific gene, known as GDF9B, influenced the ability to have twins or triplets.

Ewes with one copy of the mutation have enhanced fertility, while those with two copies are infertile. Scientists also discovered that the gene was switched on at a particular stage during pregnancy.

The structure of the gene in women and sheep is very similar.

Dr McNatty said that the implications of the find were enormous.

It showed that the GDF9B gene was essential for normal development of an egg in sheep and that mutations in that growth factor could either improve fertility or switch it off.

Many ovarian defects were linked to mutations in the X chromosome and understanding the controlling agents, including GDF9B, within the ovary meant understanding the key to fertility itself.

"It can't get any better than this," he said. "The discovery has been released worldwide and it will open up a whole new branch of science.

"People throughout the world will be working on this."

Scientists in New Zealand, Australia and Finland, who collaborated on the research, were working with women to discover the extent of the implications for human fertility, he said.

It was the first time that a gene had been found to act directly on the ovary to increase egg production rather than through the pituitary gland.

In much the same way that contraceptives interfere with the production of hormones in the pituitary gland, the GDF9B gene might lead to a safer contraceptive.

The gene's influence showed that "the egg within the ovary connects with the cell around it," said Dr McNatty.

Although it was pure speculation, a drug could be developed to interfere with the signal between the egg and the cells around it, he said.

Similarly, infertile women might possess the double mutation that caused barrenness in sheep, leading to treatment of the real causes of sterility.

Dr Galloway said the discovery could lead to increased productivity for sheep farmers, by producing more lambs from the same number of ewes, and allow AgResearch to develop a test for identifying carrier rams and ewes.

- STAFF REPORTER, NZPA