Around a third of all couples between the ages of 25 and 50 want children – but it doesn’t work. It is not always possible to clarify why this is the case. Research from Münster provides new information.
Many couples in Germany want to have a child, but have problems getting pregnant. The causes for this are diverse and only partially known. The study situation is particularly incomplete when it comes to male infertility; for years there has been little to no research into it.
In a third of men who are proven to be medically infertile, sperm testing cannot explain the cause. Because for them, the “semen analysis under the microscope initially looks completely inconspicuous and normal,” explains reproductive medicine specialist Timo Strünker from the University of Münster. Everything about the sperm seems to be as it should be: they swim well and are also present in sufficient quantities. Nothing indicates a problem.
Nevertheless, these men cannot father children. “And of course that’s a problem because with these men, where everything supposedly looks normal under the microscope, you don’t know what therapy to offer these couples.” Affected couples therefore often report many unsuccessful attempts to become pregnant.
The sperm lack the turbo
The interdisciplinary research team from the University of Münster succeeded in discovering a common cause of this form of infertility by examining almost 2,300 men. They were able to identify a defective ion channel, called CatSper, which regulates the calcium balance of the sperm.
To explain: sperm have several of these so-called ion channels. Their interaction is necessary so that the sperm cells in the female body can move to the egg cell. By giving them the momentum they need to move forward. This is because these channels control both the electrical excitation and the ion balance of the sperm and thus their drive unit. CatSper is the name of the channel that is responsible for ensuring that the sperm cell switches on the turbo and can thus overcome the last hurdle on the way to the egg cell.
“We were able to determine that this channel in these sperm does not work at all or does not function properly,” says doctor Strünker. “And this means that the sperm can no longer drill through the protective shell of the egg.” But this is the last and necessary step so that the egg cell is fertilized. “If this CatSper channel doesn’t work properly, then the sperm can’t do it. And, figuratively speaking, they get stuck in the egg shell.” And this means that neither fertilization of the egg nor pregnancy is possible.
“A piece of our DNA is missing”
To find out why this channel doesn’t work, another team from the University of Münster examined the genetic makeup of these men – and actually found a genetic deviation. The gene for the CatSper channel was either not completely present in them or was even completely missing, explains reproductive geneticist Frank Tüttelmann.
“A piece of our DNA, our genetic material, is missing. This gene is not there at all, it is not formed at all. And accordingly the channel does not work.” And since it is a genetic abnormality, it cannot be easily repaired. Sperm function cannot therefore be restored in such a case.
Under the microscope, the sperm of the affected men look “normal”. But they are missing an important ion channel.
Fertility treatment could be adjusted
Therefore, couples with this genetic peculiarity only have one way out to fulfill their wish of having a biological child: the so-called ICSI method, with which the sperm are injected directly into the egg in a test tube. However, this method is usually not the first priority in treatment in many fertility centers, says doctor Strünker. This is why couples for whom there is no clear indication of the exact cause of male infertility often undergo numerous fertility treatments, all of which fail.
Both the so-called insemination, in which the sperm are brought into the uterus, and the so-called in-vitro fertilization, in which the egg and sperm cells are brought together in a test tube, are futile if the CatSper canal is defective. Therefore, the knowledge gained now makes it possible not only to identify the cause of male infertility, but also to apply fertility treatment that is actually promising, says Sabine Kliesch, chief physician in the Department of Clinical and Operative Andrology at the University of Münster.
And reproductive medicine specialist Strünker emphasizes that this finding means a significant improvement in fertility treatment, especially for women: “I don’t know of any other clinical picture where I, as a man, am sick and in the end the woman is treated and has to bear the medical risk. In fact “It’s the case that you can save the couple, i.e. the woman, unnecessary hormone treatments and stimulation and egg collection and can directly choose the method that leads to success.”
Test already available
The laboratory test that researchers at the University of Münster developed to find out whether the CatSper channel works or not has already been certified. The researchers say it should be as easy to use as a rapid Covid antigen test. And that means that it is already available to fertility centers.
But this does not mean that all the mysteries surrounding male infertility have been solved: the CatSper canal is certainly not the only cause of it, says reproductive medicine specialist Strünker. That’s why the scientists at the University of Münster are continuing to work on the topic. Research funding from the German Research Foundation has already been approved for this.