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2011-07-21 08:19:24
By Helen Briggs Health editor, BBC News website
As many as a quarter of men have a genetic change which makes them less fertile
than usual, research suggests.
The discovery could lead to a new screening test to identify those who will
take longer to father a child, experts report in the journal Science
Translational Medicine.
The change is in a gene that codes for a key protein found on the outside of
sperm.
Sperm lacking in the substance find it harder to swim to the egg.
Researchers believe a man with the altered gene can still get his partner
pregnant, but this will take longer than usual.
Dr Edward Hollox of the University of Leicester is a co-author of the study.
Start Quote
We understand little about the subtle molecular events which occur in sperm as
they make their journey through the woman's body to fertilise an egg
Dr Allan Pacey University of Sheffield
He told the BBC: "If you've got this gene variant you should allow that little
bit longer if your partner's planning to get pregnant.
"It takes two - it's the genetic variation in a man that affects fertility in
this particular case."
Molecular events
He said the discovery raised the possibility of a new test to identify couples
who might need fertility treatment.
"It's another tool in the toolkit of fertility treatment," he said.
The genetic change is in a gene called DEFB126, which codes for a protein that
clings to sperm, helping them swim through the woman's body to fertilise the
egg.
Abnormal sperm These sperm look normal but have more difficulty getting to the
egg
Researchers believe men with the defective gene have sperm that find it harder
to make their way through mucus, causing low fertility.
A study of more than 500 married couples in China found that women who had
partners with two copies of the defective gene (one from the mother and one
from the father) were less likely to get pregnant.
The women also took longer to get pregnant by a couple of months.
Further studies, carried out in people from the US, UK, China, Japan and
Africa, found the gene mutation is common around the world.
About half of all men carry one copy of the defective gene; while a quarter
have two defective copies.
Male infertility
Infertility affects around 10 to 15% of couples
About half of these cases involve problems in men
Most cases of male infertility are unexplained, driving the search to find new
tests and possible treatments
Commenting on the study, Dr Allan Pacey, Senior Lecturer in Andrology at the
University of Sheffield, said:
"We actually understand very little about the subtle molecular events which
occur in sperm as they make their journey through the woman's body to fertilise
an egg.
"We know even less about how a man's genes may contribute to how his sperm
work, in the absence of an obvious defect that we can see down the microscope.
"Therefore, this paper is an important step forward and makes a significant
contribution to our sperm-knowledge."