Said team of international researchers about 20 percent of men may harbor gene mutations that allow sperm coat-free and thus a lower birth rate, on Wednesday.
Says study co-author Dr. Theodore Tollner, University of California, Davis performance tests today can not solve the problem.
"You'll have no reason to believe many of these people with genetic mutations and reduced sperm function," he said.
And can be anywhere from 10 percent to 15 percent of couples experience infertility, and doctors do not always find a reason. Lack of sperm, or problems with the form or explain their ability to move only a small part of infertility.
The team found California brought a new reason, a protein that is part of a family of molecules that kill microbes on the surface of various tissues. Secreted as a journey of the sperm in the female reproductive system and helps the sperm to penetrate cervical mucus in women, and to avoid being tagged as an invader by the immune system to it.
The presence of two copies of a specific gene mutation means that sperm can not produce the paint. Laboratory tests showed that their sperm is difficult to do so by mucus.
But to what extent affect fertility?
Researchers then 500 couples from China recently married trying to conceive. Researchers reported in the birth rate is 30% among couples with one spouse who harbored a double mutation in the journal Movement Science Medicine.
The mere presence of one copy of the mutated gene does not seem to prevent pregnancy.
Sperm coatless not always fail, so it is unclear how much of this contributes to male infertility in general.
But the creation of a test to diagnose these people will not be easy, researchers say. This test will reduce the time that is likely to spend a few problems of pregnancy in trouble before trying to treat, such as the presence of semen and placed directly into a woman's uterus.
One day it may be even vaginal gel protein coating the sperm to catch that is transmitted to the cervix. California researchers say they already try that with animals.