A study, published in the journal Science Translational Medicine, has found that a mutated gene may be responsible for the infertility of some men. Researchers have found that the carbohydrate coating on sperm is often removed in some men. This lack of a coating in turn reduces mobility of the sperm and so it cannot fertilise the woman’s egg effectively.

The researchers also found that couples have greatest trouble conceiving if men have inherited both copies of this mutated gene from the mother and father.

The carbohydrate coating is thought to help the sperm travel freely through fluids. Its absence slows it down markedly. The gene in question is DEFB126.

Speaking with reporters one of the leaders in the study, Theodore Tollner said: “We found that sperm from donors lacking the normal gene have difficulty penetrating or swimming in the mucus surrogate (on laboratory dishes).”

He added: “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.”

Male infertility is a major problem worldwide and is something that until now has not been as widely acknowledged. Infertility is defined by the World Health Organisation (WHO) as the inability of couples to conceive after 12 months of unprotected sex. It is a problem currently affecting about 13% of couples internationally and some countries, notably India appear to have a higher prevalence.

Until now, male infertility has traditionally been blamed on low sperm count, but this latest research may force medical scientists to re-think their views.

This view was confirmed by Steven Rozen of Duke University who said: “[If this research is true it] 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.”