1. The absence of sperm in the testicles or the absences of testicles, described as non-obstructive azoospermia, are the most basic factors of male infertility. The causes that lead to these situations are
- Chromosomal or genetic abnormalities such as deletions of chromosome parts or genes
- Inability of testicular descent
- Surgical removal of the testicles due to testicular tumors that are common in young ages
- Mumps disease, that may only affect spermatogenesis if it occurs during adolescence or after that stage
- Chemotherapy or radiotherapy
