Genetic sperm 'invisibility cloak' clue to infertility

A team of international
scientists has found a common genetic variant which may explain why some men
with normal sperm counts and good quality sperm are affected by infertility.

The study findings suggested
that men with a variation in a gene which codes for a sperm-coating protein called beta defensin 126 (DEFB126) have a reduction in the protein coat on the
outside of the sperm which makes it difficult for the sperm to 'swim' to the
egg.

Dr Edward Hollox of the University of
Leicester and co-author of the study said:
'If you've got this gene variant you should allow that little bit longer if
your partner's planning to get pregnant'.

The researchers, including scientists from the
University of California and the Anhui Medical University in
China, carried out the study on over 500 newly-wed Chinese couples who were
trying for a baby. They found that when men's sperm lacked a coat of the DEFB126 protein, their wives were
significantly less likely than expected to become pregnant.

Previous studies have
shown that two copies of the genetic variant may be found in up to one quarter
of men around the world, with about half of all men having one copy. The
DEFB126 protein coat helps sperm to swim through cervical mucus and evade the
woman's immune system, as well as enabling it to attach to the walls of
fallopian tubes.

The study showed, however, that men with two copies
of the variantproduced sperm that were less able to swim through a substitute to cervical
mucus, hyaluronic acid gel. In macaques, it has already been shown that this
protein is important in evading the immune system and the researchers believe the
protein coat plays the same role in humans.

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'.

The research was
published in the journal Science Translational Medicine.