Scientists discover enzyme that controls ovulation

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A cause of premature menopause has been found which could pave the way to new treatments and also help improve the success of test tube baby fertility treatments.

An international team that includes British scientists has discovered an enzyme that controls the rate at which women ovulate and believe that when this process goes awry it can lead to menopause occurring years earlier than normal.

At birth, the ovaries of women contain about 300,000 - 400,000 unripe eggs, her lifetime's complement, each held in a tiny sac or follicle.

But in adulthood only ten or so follicles grow each month and of these, only one goes on to deliver an egg bursting to release its ripened egg into the fallopian tube.

However, around one woman in every hundred runs out eggs before her 40th birthday, triggering early menopause, so she is no longer able to have children naturally.

Today, in the journal Science, Dr Kui Liu of Umeå University, Sweden, Prof Ilpo Huhtaniemi of Imperial College London and colleagues in China and America report that the enzyme PTEN keeps immature eggs from ripening prematurely. "It is a kind of brake," says Prof Huhtaniemi.

The team finds that in mice lacking PTEN in their eggs, the entire pool of immature eggs is activated prematurely, becoming ripe so the mouse uses up it store of eggs more rapidly..

Prof Huhtaniemi says that PTEN works in humans too and that the team is now going to investigate whether mutations in the PTEN gene are linked with premature menopause in women. "We have one good candidate to explain why some women develop premature menopause," he says.

A drug to mimic the effects of PTEN could be used to prevent or treat premature menopause when combined with new tests that can show how quickly a woman's biological clock is ticking. By the same token, a way to block the effects of PTEN could lead to new ways to ripen eggs for IVF, notably if eggs fail to ripen in the first place, says Dr Liu.

To overcome how women only make one egg each month and obtain more for IVF treatments, or to create embryos if they are to undergo fertility threatening cancer treatments, doctors have used expensive hormones to stimulate them to ripen multiple eggs, which does carry some risks.

But some women seeking to preserve their child-bearing capacity may not have enough time to undergo ovarian stimulation or may have a condition that makes it dangerous, such as hormone-sensitive breast cancer.

Lab-dish or "in vitro" egg maturation has produced hundreds of babies worldwide, though is still experimental.

Now PTEN offers another way to ripen eggs, says Dr Liu. "With the knowledge that PTEN suppresses follicle activation, it is in theory possible to culture a piece of the ovaries in the petri-dish and trigger the follicle growth with a synthetic PTEN inhibitor, which we have started to try".

Such a method will enrich the source of eggs for IVF or who want to freeze their embryos before going to have chemotherapy or radiation therapy for cancer, says Dr Liu.

Source: http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/01/31/scimeno131.xml

Category: early menopause, Egg Freezing, IVF, menopause, Old Eggs, ovulation, perimenopause