Male contraceptive pill is a step closer after gene discovery

A contraceptive pill for men which works by preventing sperm development could result from the discovery of a new gene, scientists have said.

The gene, which is active in the testes, controls the final stages of sperm development. Blocking it would result in temporary infertility, without permanently damaging a man's sperm-making machinery, the researchers said.

One of the greatest problems associated with developing a male contraceptive is knowing how to block the immense sperm-producing factories of the testes with near 100 per cent reliability but without long-term damage.

Several attempts at making a contraceptive based on blocking testosterone have run into difficulties, not least because of adverse side-effects such as irritability, tiredness and loss of sex drive.

But scientists believe the discovery of a gene called Katnal1 could provide a potential solution given its pivotal role in the last stages of sperm development.

When the gene is blocked, the testes continue to make sperm, but only ineffective, immature sperm are released, said Lee Smith of Edinburgh University. "The effects of such a drug would be reversible, because Katnal1 only affects sperm cells in the later stages of development, so it would not hinder the overall ability to produce sperm," he said.

The scientists, funded by the Medical Research Council, discovered Katnal1's role by analysing the DNA of infertile male mice that had suffered mutations to their genetic material.

Further research, published in online journal PloS Genetics, revealed Katnal1 controls the fine network of microscopic tubes that supply nutrients to the final developmental stages of sperm cells just before they are ready for release.

When Katnal1 is blocked, the microscopic tubules break down earlier than they should, which arrests sperm development. The result is that the sperm cells are released in an immature state, making them incapable of fertilising an egg cell, Dr Smith said. "Although other research is being carried out into non-hormonal male contraceptives, identification of a gene that controls sperm production is a unique and significant step forward," he said. But he added it will still take years before potential drugs can be tested on men.