A gene inherited from their mothers raises men's risk of testicular cancer by up to 50 times, scientists have discovered.
Scientists said the gene was thought to account for about one third of cases of inherited testicular cancer. Within two to five years they expect to isolate the gene, allowing men with the abnormality to be identified and treated earlier and more successfully.
The gene, the first linked with the disease to be located, lies somewhere within a region of about 300 genes on the female X chromosome.
Experts believe as many as 20 per cent of cases involve an inherited susceptibility linked to at least three genes. The risk of testicular cancer is increased eight to 10 times in a man whose brother has had the disease.
There were 102 cases of testicular cancer reported in Ireland in 1996 - the most recent statistics available. The disease accounts for about 1 per cent of Irish cancers. However, the numbers of testicular cancers are increasing, the Irish Cancer Society said.
The discovery, reported in the journal Nature Genetics, followed 10 years' work, including research at St James's Hospital, Dublin. Researchers from Britain, Norway, Germany, Australia and Canada also contributed.
The British-led team behind the research said they homed in on the gene, given the name TGCT1, after analysing blood samples from members of 134 families with two or more cases of testicular cancer.
A leading member of the team, Prof Mike Stratton, from the Institute of Cancer Research in Sutton, Surrey, said: "The major implication is that if we can identify individuals who are carrying abnormal copies of this gene before they are affected, it will be possible to implement screening procedures that will allow us to detect cancers early, and with early detection the cure rate is very high."
Prof Stratton, who led the team that discovered the breast cancer susceptibility gene BRCA2 in 1995, said tracing the genes linked to testicular cancer may also help improve the treatment of other cancers. For some unknown reason testicular cancer was unusually responsive to treatment, and more than 90 per cent of new cases were cured with chemotherapy.