A young man shows up at the medical appointment with an unfulfilled desire to have children. However, the spermiogram shows normozoospermia. So the problem could be on the female side? The man also has poor hearing. Would you think of a genetic defect? According to a new exciting study, presented during the 2020 congress from the German Urological Society (DGU), you should consider genetics in the future.
In a spermiogram, men with deafness infertility syndrome (DIS) do not show any deviations compared to a normal assessment. The sperm count is as normal as their morphology and motility. And yet those affected suffer from infertility. In addition, hearing loss/hearing impairment often occurs.
The genetic defect that explains both symptoms is found on chromosome 15, according to recent research. There, the gene for stereocilin (STRC) and the gene for a subunit of the CatSper ion channel (CATSPER2) are simultaneously deleted. As a result, there are functional restrictions in the hearing sensory cells, but also a loss of fertility in the sperm, in which the CatSper calcium channel required for this becomes inoperable. Affected men then typically range from hearing-impaired to deaf, and are infertile.
On their way to the egg, sperm have to cross the cumulus oophorus cluster and the pellucid zone to reach their destination. To do this, the sperm increase their beat rate. This is triggered by progesterone in the vicinity of the egg cell. This hormone activates the CatSper calcium channels in the sperm, allowing calcium ions to flow in. The calcium flow, in turn, causes the sperm tail to rotate more quickly, finally changing from a symmetrical flagella beat to the "hypermotile" phase. In men who lack the CATSPER2 gene, the calcium channel no longer functions, so that no calcium can flow in and no change in activity takes place at the end. The sperm no longer penetrates the egg, resulting in infertility.
Statistics have previously shown that the proportion of infertile men with normozoospermia comprises about 30% of all infertility patients observed in medical practice. However, it remains unknown how large the proportion is of those who suffer from DIS.
However, a functional test ("CatSper activity test") could soon help here, which provides a result in just a few minutes to determine whether or not a CATSPER2 deletion is present. The lower the CAT index, the more likely it is that the sperm cells tested have such a defect. But why is it so important in practice to know about this defect?
A study has shown that men with deafness infertility syndrome can only achieve success in assisted reproduction with ICSI (Intracytoplasmic Sperm Injection). This means that it is absolutely necessary for these patients to bring sperm and egg directly together. All other procedures failed because the sperm could not trigger a calcium-dependent motility change.
Source:
Young S. Deafness-infertility syndrome: a model to unravel the role of CatSper in human sperm (dys)function. DGU (German Urological Society) Congress 2020