Gene key to sperm power

The gene is crucial in the production of sperm

Some cases of male infertility may be caused by a gene defect which could rob the sperm of power, say scientists.

It could be a factor in at least five to 10 per cent of male infertility cases, they believe.

If confirmed, it could lead to early detection through screening, saving couples the heartache of trying and failing to conceive over many years.

The international study, published on the website of the journal Nature Genetics, looked at a genetic mutation affecting a gene called POLG.

The information would be very valuable to an individual, who could be alerted to the problem even before reaching reproductive age

Professor Howy Jacobs

The gene plays a role in the replication of DNA within mitochondria, components of cells which help produce enough energy to make them work.

If the mitochondria in sperm cells do not function correctly, the theory is that sperm may not be able to swim vigorously enough and so fail to fertilise the egg.

Between one on five and one in 10 couples are affected by fertility problems.

In around half of cases, it is the man's fertility which is affected.

Many cases have a genetic cause.

Poor quality sperm link

The study found the mutations of the POLG were associated with poor sperm quality, but had no other obvious consequences.

Women with the mutation appeared to be completely healthy.

The researchers estimate up to 2% of the population have the POLG mutation, and that it may cause up to 10% of male infertility cases.

The mutation has been found in men with moderately low sperm counts combined with a variety of other sperm abnormalities, such as abnormal cell structure or the inability to swim.

Professor Howy Jacobs, of the University of Tampere, Finland, who led the study, said it was believed the mutation affected the amount or integrity of mitochondrial DNA in the sperm cells, damaging their energy-producing ability.

He said further research would be carried out to confirm their supposition.

Access to early help

He told BBC News Online that: "The good news is that because men affected by POLG-associated infertility do produce at least a few relatively normal sperm, simple procedures of 'assisted reproduction', such as IVF and especially ICSI may be an appropriate therapy."

He added: "POLG mutations associated with male infertility can be easily detected using a simple DNA screening procedure.

"Such a screening could easily be incorporated into a routine set of genetic tests offered at any age - even, for example, in childhood.

"The information would be very valuable to an individual, who could be alerted to the problem even before reaching reproductive age.

"He could thus be provided with appropriate counselling and effective therapy when he chooses, instead of wasting many desperate years trying but failing to produce children."

Professor Jacobs added: "Long-term ignorance of the problem carries a large cost in terms of wasted time, expensive medical investigations, damaged relationships, injured self-esteem and depression, often culminating in permanently disrupted family life.

"Early diagnosis could be hugely beneficial in alleviating this burden."