Insight Into Male Infertility

A team of Mayo Clinic researchers led by Jan van Deursen, Ph.D., including Ningling Kang-Decker, Ph.D., George Mantchev, M.D., Subhash Juneja, Ph.D. and Mark McNiven, Ph.D., identified that the Hrb protein affects the sperm's ability to fertilize an egg. In the study, researchers deleted the gene that produces the Hrb protein in mice, which made the mice infertile. They concluded that this lack of Hrb protein prevents the acrosome from forming, making egg penetration impossible. The acrosome, which develops as the sperm matures, is a structure that contains a bag of enzymes covering the head of the sperm. The enzymes contained in the acrosome help penetrate and digest the outer sheath of the egg, thereby allowing conception.

"It has long been known that healthy acrosome development is essential for fertility and is often defective in men with certain types of infertility," says Dr. van Deursen. "This study now identifies the specific protein needed for healthy acrosome development, resulting in fertility."

Dr. van Deursen says that although male infertility has many causes, if there is a link between defective Hrb protein and acrosome development, future screening for this protein deficiency may help eliminate that as a specific cause of infertility.

"The findings will not lead to immediate therapeutic advances in fertility treatment," says Dr. van Deursen. "However, the findings provide valuable insight into the molecular basis of fertility."

He adds that the next step will be to study infertile men to determine if they have the defective Hrb protein. This will enable researchers to further define the importance of Hrb in acrosome formation.

"By understanding how healthy cells should function, we will eventually understand and identify defective cells," says Dr. van Deursen. "This is a first step in understanding male infertility."

About one in 12 couples in the United States is affected by infertility which is defined as the inability to conceive after at least one year of trying. Ten to 15 percent of couples are infertile. Of these couples, a problem occurs in the male reproductive system in about 30 percent of cases and contributes to the infertility problem in an additional 20 percent of cases.