A single gene may be crucial for the final stages of sperm cell formation and could help explain why some men are infertile, U.S. researchers said on Wednesday.

Laboratory mice who lacked the gene had a significantly lower sperm count and were infertile, researchers at the University of North Carolina at Chapel Hill discovered.

And the few sperm the mice did produce had significant defects, they said.

"Because this gene has a very specific effect on the development of functional sperm, it holds great potential as a target for new infertility treatments," Yi Zhang, a professor of biochemistry and biophysics at the university`s school of medicine, said in a statement.

About 1 in 6 couples in the United States has difficulty conceiving a child, according to the National Institutes of Health. In 30 to 40 percent of these 2.6 million couples, the men are infertile.

Zhang`s study, which appears in the journal Nature, focused on the last stage of sperm cell formation known as spermiogenesis. During this phase, DNA is crammed into a tight ball at the head of the sperm, ensuring that it can successfully penetrate an egg.

Mice bred to lack a gene responsible for this process produced few mature sperm, and the few that were produced had abnormally shaped heads and immobile tails.

"This gene is very important in controlling key genes that are involved in compacting the DNA," Zhang said in a telephone interview.

In the mutant mice, Zhang and colleagues detected a defect in sperm DNA packaging. The mice also had smaller testes, but Zhang said this was because the testes were not filled with sperm as they should be.

He said more work needed to be done to discover whether this same defect causes infertility in men.

"The first thing we need to know is whether people have mutations of this gene," said Zhang, who plans to team up with researchers studying this infertility syndrome in humans.

Ultimately, he said this discovery could lead to the development of a drug that compensates for mutations in the gene.

"That possibility is there, but it is not going to happen tomorrow," Zhang said.

The research was funded by the Howard Hughes Medical Institute and the National Institutes of Health.
sections: Nature & Health