Testicular factor infertility is infertility due to factors that directly affect the testicles. These factors can be congenital, due to causes present from birth or environmental. The most frequent genetic alterations are microdeletions of the Y chromosome and Klinefelter's syndrome.
The Y chromosome is only found in males and contains the genes responsible for the formation of the testes in a region called the AZF region. If there is an alteration in this region, the male will have a severe male factor, such as oligoasthenozoospermia or even azoospermia.
On the other hand, Klinefelter syndrome is a genetic alteration in which the male has three sex chromosomes instead of two, with the karyotype being 47 XXY. The result of this alteration is a male with insufficient production of testosterone, so that a correct development of the reproductive system does not occur, leading to azoospermia.
There are other non-genetic testicular alterations that are responsible for infertility. The most important of these is varicocele. It is a dilatation of the testicular vessels that can affect fertility. If it is very evident it can cause pain. Symptomatic cases may benefit from surgical intervention.