Scientists dicover male fertility gene in mice

(CNN) -- Researchers at the Salk Institute have found a gene that when altered can make male mice infertile without other side effects, such as loss of hair, growth of breasts or sexual dysfunction, according to a study in the journal Nature Genetics.

The study authors said they accidentally discovered this male fertility gene when they identified a tiny piece of genetic code which stops sperm from maturing, thus making the sperm incapable of fertilizing an egg.

"That resulted in male mice that were completely sterile," said Dr. Peter Blume-Jensen of Salk Institute.

The altered mice act like normal male mice -- they can and do mate.

Even though it is years away, scientists hope this genetic discovery could eventually lead to a male birth control pill without side effects.

But currently the genetic change in these mice is permanent. For this therapy to be used as a male contraceptive, the genetic change would have to be reversible and scientists don't yet know if that is possible.

"Our next step will be to make what's called a regulated change in the mouse so we can turn this change on and off at the gene level," said Tony Hunter, Salk Institute molecular biologist. "That will be difficult, but I think that can be done."

The researchers said they will have to study generations of these genetically altered mice to make sure there are no long-term side effects, but so far they have found none. They will also have to make sure these mice studies can then be applied to men.