When semen parameters are lower, it is worth considering the performance of genetic diagnosis. Genetic defects can also be the cause of these abnormal parameters. The basic markers which are analyzed for infertility are mutations in the Cystic Fibrosis gene which contribute to the development of mucoviscidosis. And in the cases of incomplete disease, they may concern solely lower semen parameters. Another test we recommend for male patients is the test for the presence of the AZF factor, i.e. mutations in a part of the gene located on Y chromosome, leading to a significantly decreased number or lack of sperm. The causes of male infertility may also be mutations in all fertility receptors and hormones, which means that both mutations in FSH hormone and its receptor or in LH hormone and the receptor for LH -HCG may induce infertility or fertility disorders. The receptor for androgens is also frequently checked.