“I’ve got swimmers!” One of our patients actually listed this as the reason he was ready to discard the sperm he had banked with us prior to starting cancer treatment. I laughed aloud when I read it. What a humorous way of telling us that he recently had a semen analysis that demonstrated good motility and forward progression.
Being a swimmer (good motility) is critical to sperm’s ability to fertilize an egg. Sperm start to move once they’ve been ejaculated from the male urethra. However just because they’re moving doesn’t mean they’re able to fertilize an egg. First sperm must undergo a maturation process called capacitation. Capacitation involves the movement of calcium ions into the sperm cell. The calcium ions move into the sperm cell through specialized ion channels named CatSper. Once inside the cell, the calcium ions trigger a series of events that will hyperactivate sperm motility. In the female reproductive tract, hyperactivated motility occurs right by the egg, at the site of fertilization, and enables the sperm to penetrate the egg and achieve fertilization.
Sperm that are unable to undergo capacitation cannot penetrate an egg and thus fertilize it. Researchers have discovered two gene mutations that cause sperm to be produced without CatSper channels. These genes are CatSper1 and CatSper2. Men with either of these mutations are infertile.
Clinically diagnosing CatSper-related male infertility can be tricky. Changes in motility caused by the absence of CatSper channels are frequently missed in standard semen analyses. “A more rigorous clinical examination that includes measurement of sperm motility parameters like path velocity, progressive velocity, and track speed”1 is required to help determine if sperm cells are hyperactivated. Computer-aided sperm analysis (CASA) systems have been developed that are capable of performing this type of assessment of motility. Genetic testing is also available to confirm a diagnosis of CatSper-related male infertility.
If lack of CatSper channels is the cause of a couple’s fertility woes, there is no treatment option available that will enable them to achieve a pregnancy naturally. However, pregnancy can be achieved with intracytoplasmic sperm injection (ICSI) using sperm from ejaculate, testis tissue, or epididymal tissue.
Hildebrand MS, Avenarius MR, Fellous M, et al. Genetic male infertility and mutation of CatSper ion channels. European Journal of Human Genetics. 2010; 18(11): 1178-1184.
Calcium Signaling Through CatSper Channels in Mammalian Fertilization, Dejian Ren and Jingsheng Xia, Physiology June 1, 2010 vol. 25 no. 3 165-1750