Scientists have identified an enzyme that controls the ovulation process in women, and is responsible for premature menopause.

The international team suggests that their findings could lead to new treatments and also help improve the success of test tube baby fertility treatments.

At birth women's ovaries contain about 300,000 - 400,000 unripe eggs, each held in a tiny sac or follicle. However, in adulthood only ten or so follicles grow each month and of these, only one goes on to carry an egg bursting to release its ripened egg into the fallopian tube.

But, in around one woman in every hundred, eggs exhaust before her 40th birthday, causing early menopause, and thus disabling her to have children naturally.

But Dr Kui Liu of Umea University, Sweden, Prof Ilpo Huhtaniemi of Imperial College London and colleagues in China and America have found the root cause of this condition - an enzyme called PTEN that keeps immature eggs from ripening prematurely.

"It is a kind of brake," the Telegraph quoted Prof Huhtaniemi, as saying.

The study on mice lacking PTEN in their eggs, found that the entire group of immature eggs is activated prematurely, becoming ripe and thus the mouse consumes it's store of eggs more quickly.

Prof Huhtaniemi said that PTEN works in humans too, adding that the team is now going to look into whether mutations in the PTEN gene are associated with premature menopause in women.