Risk factors for the formation of antisperm antibodies in men include the breakdown of the blood‑testis barrier, trauma and surgery, orchitis, varicocele, infections, prostatitis, testicular cancer, failure of immunosuppression and unprotected receptive anal or oral sex with men. Genetics
Chromosomal anomalies and genetic mutations account for nearly 10–15% of all male infertility cases. Klinefelter syndrome
One of the most commonly known causes of infertility is Klinefelter syndrome, which affects  one in 500–1000 newborn males. Klinefelter syndrome is a chromosomal defect that occurs during gamete formation due to a non-disjunction error during cell division. Resulting in males having smaller testes, reducing the amount of testosterone and sperm production. Males with this syndrome carry an extra X chromosome (XXY), meaning they have 47 chromosomes compared to the normal 46 in each cell. This extra chromosome directly affects sexual development before birth and during puberty. A variation of Klinefelter syndrome is when some cells in an individual have the extra X chromosome but others do not, referred to as mosaic Klinefelter syndrome. The reduction of testosterone in the male body normally results in an overall decrease in the production of viable sperm for these individuals thereby forcing them to turn to fertility treatments to father children. Y chromosome deletions
Y chromosomal infertility is a direct cause of male infertility due to its effects on sperm production, occurring in approximately one in 2000 males. Usually, affected men show no symptoms, although they may have smaller testes.
If reproduced in humans, this could potentially enable infertile men to father children with their own sperm.Researchers from Montana State University developed precursors of sperm from skin cells of infertile men.Sharpe et al. comment on the success of intracytoplasmic sperm injection (ICSI) in women saying, "[t]hus, the woman carries the treatment burden for male infertility, a fairly unique scenario in medical practice. Ironically, ICSIs success has effectively diverted attention from identifying what causes male infertility and focused research onto the female, to optimize the provision of eggs and a receptive endometrium, on which ICSIs success depends." Prevalence
Currently, there are no solid numbers on how many couples worldwide experience infertility, but the World Health Organization estimates between 60 and 80 million couples are affected. The population in different regions have varying amounts of infertility. Starting in the late 20th century, scientists have expressed concerns about the declining semen quality in men. A study was done in 1992 with men who had never experienced infertility showed that the amount of sperm in semen had declined by 1% per year since 1938. Further research a few years later also confirmed the decline in sperm count and also seminal volume. Various studies in Finland, Southern Tunisia, and Argentina also showed a decline in sperm count, motility, morphology, and seminal volume. Males from India had a 30.3% decline in sperm count, 22.9% decline in sperm motility, and a 51% decrease in morphology over a span of a decade.