CATSPER2 and Infertility: In addition, the gene expression of CatSper1, 2, 3, and 4 was lower in infertile men with AZS as compared with fertile individuals with normal sperm parameters 20, and the mRNA levels of CatSper2 and CatSper3 in the low-motile spermatozoa were lower than those in the high-motile fraction of human ejaculated spermatozoa 21.