* Mutant gene causes loss of sperm coating, mobility
* May be linked to lower conception rates, China study finds
By Tan Ee Lyn
HONG KONG, July 21 A genetic mutation that
removes a coating of carbohydrates around sperm reduces their
mobility and may explain why some men are less fertile than
others, researchers said on Thursday.
The study, published in the journal Science Translational
Medicine, found that couples who had the most trouble conceiving
were those where the men inherited both copies of this mutant
gene, one from their father and one from their mother.
The loss of this coating makes it more difficult for sperm
to travel through fluids in the female reproductive tract, which
in turn reduces the rate of conception, lead author Theodore
Using semen donated from 19 participants, Tollner and
colleagues observed that sperm from donors who had both copies
of the mutant DEFB126 gene exhibited most mobility problems.
"We found that sperm from donors lacking the normal gene
have difficulty penetrating or swimming in the mucus surrogate
(on laboratory dishes)," wrote Tollner, assistant adjunct
professor at the Center for Health and the Environment,
University of California.
"The rate at which they are able to penetrate the mucus-like
gel is only 15 to 20 percent of the rate observed for sperm from
donors with the normal gene," Tollner said in an email, replying
to questions from Reuters.
The World Health Organisation defines infertility as the
inability of a couple to conceive after a year of unprotected
sex, and the problem occurs to around 13 to 14 percent of
couples in many countries across the world.
In about half of infertile couples, the cause lies with the
men and experts have traditionally blamed low sperm count. This
paper by Tollner and colleagues is the first time that experts
are pointing to the loss of a coating around sperm.
Steven Rozen of Duke University-NUS Graduate Medical School
Singapore, who was not related to the study, said this genetic
mutation is "quite common".
"That means that a large proportion of men would be
affected. Depending on the population, 20 percent to 30 percent
of men have two copies of the low fertility variant, which means
their sperm lack the coating," Rozen told Reuters.
To test their hypothesis, the scientists recruited 509 young
couples in China and tracked them for nearly two years. The
average age of the men was 25.8 and the women 23.4.
The couples were put into three groups depending on the DNA
of the men: men without the gene mutation, men with one copy of
the mutant gene and men with both copies of the mutation.
By the end of the study, wives of 71 percent of men with
both copies of the mutant gene had conceived, compared to 81
percent of wives of men with either one or none of the mutant
"Our key finding was that the rate of births among couples
where the husband had two copies of the DEFB126 mutation was 30
percent lower than in other couples," wrote Scott Venners,
assistant professor of epidemiology at the Simon Fraser
University Faculty of Health Sciences.
"This most likely indicates that the DEFB126 mutation
reduced the rate of conception in these couples and so it took
them longer to achieve pregnancy," he told Reuters.
When helping couples conceive, doctors may consider using
more direct interventions such as in vitro fertilisation or
intrauterine insemination if they find that the male partner has
this gene mutation, Tollner said.
(Reporting by Tan Ee Lyn; Editing by Daniel Magnowski)