Couples unable to conceive may soon be better able to pinpoint the cause of their problem. According to a report in the journal Human Reproduction, a team of American and Japanese scientists has developed a test for male infertility that surpasses conventional semen analysis.

The new method, called sperm-ubiquitin tag immunoassay (SUTI), searches sperm cells for a small protein known as ubiquitin, an indicator of damage or defect. Using ubiquitin antibodies to screen sperm from 17 infertility patients and two fertile donors, the researchers confirmed previous diagnoses in some cases and revealed reasons for infertility that had been inexplicable in others. "Ubiquitin appears to be a universal marker of semen abnormalities, recognizing a wide range of sperm defects and also contaminants in semen," says team member Peter Sutovsky of Oregon Health Sciences University. "In around one fifth of all couples, current methods cannot identify a cause," he adds. "SUTI will be able to provide an answer in at least a portion of these cases."

What is more, SUTI may even play an active role in treatment, team member Gerald Schatten notes. "Since we now know a specific protein that is associated with defective sperm and we have antibodies against it, there is a chance that we could develop a technique for depleting most of the truly defective sperm from semen samples for [in vitro fertilization] or intracytoplasmic sperm injection (ICSI)the process by which an egg is fertilized by injecting a single sperm."