In about one-sixth of the cases of male infertility, men do not make any measurable levels of sperm, a condition called azoospermia.

New research led by University of Pennsylvania scientists suggests that mutations in an X chromosome gene called TEX11 are responsible for about 1 percent of azoospermia cases.

The investigators also found that in mice bred to lack the gene, reintroducing the gene restores their fertility.

Additional studies in mice revealed that a certain amount of the TEX11 protein expressed from the gene is needed for sperm to form.

The protein plays an important role in the chromosomal arrangements that take place as sperm cells divide.

The findings could have important implications for diagnosing and treating certain cases of azoospermia in men.

"Identification of mutations in this X chromosome gene would improve genetic counseling for couples seeking infertility treatment, " said Dr. P. Jeremy Wang, senior author of the EMBO Molecular Medicine study.