The gene that causes infertility in men has been discovered by scientists from the Pasteur Institute in France and University College London.
Mutations of the NR5A1 gene were found in a small percentage of infertile men. This gene is already known to be involved in sexual development in both men and women - it is been linked to physical defects in the development of the testicles or ovaries.
"Given the complexity of the sperm production process it is likely that many genes are involved," BBC quoted Dr Allan Pacey, as saying.
In a group of 315 apparently healthy men, the team found mutations in the gene in just seven, and closer examination revealed the men had altered levels of sex hormones and, in one case, mild abnormalities in the cellular structure of the testicles.
"We conclude that approximately 4pc of men with otherwise unexplained failure to produce sperm carry mutations in the NR5A1 gene," they concluded.
"Although this gene defect affects only a small number of men, we need more studies like this so that we can fill in the gaps in our knowledge and possibly one day build a robust diagnostic test for male fertility based on genetics," Pacey said.
The study is published in the American Journal of Human Genetics.