The cause of male infertility often escapes experts, but scientists have found a genetic mutation that appears to disrupt sperm production.
"This may be the most frequent single gene defect that is associated with male infertility known to date, with 4% of men with unexplained severe spermatogenic failure carrying a mutation," said Kenneth McElreavey, a researcher at the Pasteur Institute in France and a member of the team that made the discovery.
The gene, NR5A1, has been associated with other reproductive problems, McElreavey noted. "Studies in the last 10 years have linked mutations involving NR5A1 to defects in the development of external genitalia in boys," he said. "Last year, we identified mutations in this gene associated with a range of reproductive problems in women."
The new study links mutations in the same gene with reduced sperm count, which can lead to male infertility problems.
Male infertility is believed to account for nearly half of all infertility cases. Worldwide, about one in seven couples has problems with infertility and conception, according to the study.
McElreavey and his colleagues reported the findings in the American Journal of Human Genetics.
The researchers sequenced the gene in 315 healthy men who sought treatment for infertility because of an unexplained failure to produce sperm. They found seven men with a severe sperm production problem who carried a mutation in the gene. The defect was not found in more than 2,000 samples from a control group, for comparison.
The carriers of the mutation, McElreavey said, "may have a progressive reduction in sperm quality and quantity over time."
However, some men may be affected more than others if the findings in women - "some women carriers of the mutations have no obvious reproduction [defects]," he said - also hold true in men. The difference may stem from other genetic or environmental factors, he explained.
In the future, McElreavey added, those identified as carriers might be counselled to start a family earlier rather than later, if suspicions about the progressive nature of the defect bear out.
What's not known is whether other genes regulated by NR5A1 are also contributing to sperm production problems, he said.
Dr Robert Oates, a urology professor at Boston University School of Medicine, described the study as scientifically very sound, but offered some caveats.
The researchers found a link, but not cause and effect, he pointed out. And, the finding has no immediate practical application. "There's no commercial test for this [mutation] at this point," Oates said.
As good as the science is, Oates noted, the finding must be duplicated by other experts, in scientific fashion. For now, he said, the finding might help convince some infertility doctors not to push men to start treatment right away, without first looking for possible causes of the infertility.
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