US and Japanese scientists have developed a new test to diagnose infertility in men who produce apparently normal sperm. The teams, based at Oregon Health Sciences University and the Tohoku University School of Medicine in Sendai, Japan, hope that the new test will help doctors identify a cause in some of the 20 per cent of couples affected by unexplained infertility. Their findings could also mean fewer unnecessary procedures for women seeking fertility treatment.

The new test detects small amounts of a protein, called ubiquitin, that accumulates on the surface of damaged or defective cells. In the study, published in the latest issue of Human Reproduction, the scientists tested sperm samples from 17 patients undergoing fertility treatment. They detected a high level of ubiquitin in the sperm of five men, confirming a previous diagnosis of male infertility. They also identified five other cases in which male factors could be the cause of previously unexplained infertility. 'Ubiquitin appears to be a universal marker of semen abnormalities, recognising a wide range of sperm defects and also contaminants in sperm' said team member Dr Peter Sutovsky.

The researchers believe their discovery may also allow them to develop a new technique for removing defective sperm from samples used in IVF or ICSI (intracytoplasmic sperm injection) treatments.