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.
Animal models indicate that obesity causes leptin insensitivity in the hypothalamus, leading to decreased Kiss1 expression, which, in turn, alters the release of gonadotropin-releasing hormone (GnRH). Undiagnosed and untreated coeliac disease (CD). Coeliac men may have reversible infertility. Nevertheless, CD can present with several non-gastrointestinal symptoms that can involve nearly any organ system, even in the absence of gastrointestinal symptoms. Thus, the diagnosis may be missed, leading to a risk of long-term complications. In men, CD can reduce semen quality and cause immature secondary sex characteristics, hypogonadism and hyperprolactinaemia, which causes impotence and loss of libido. The giving of gluten free diet and correction of deficient dietary elements can lead to a return of fertility. It is likely that an effective evaluation for infertility would best include assessment for underlying celiac disease, both in men and women. Drugs, alcohol
Strenuous riding (bicycle riding, horseback riding)
Medications, including those that affect spermatogenesis such as chemotherapy, fluoxetine, anabolic steroids, cimetidine, spironolactone; those that decrease FSH levels such as phenytoin; those that decrease sperm motility such as sulfasalazine and nitrofurantoin
Genetic abnormalities such as a Robertsonian translocation

Tobacco smoking
There is increasing evidence that the harmful products of tobacco smoking may damage the testicles and kill sperm, but their effect on male fertility is not clear. Some governments require manufacturers to put warnings on packets. Smoking tobacco increases intake of cadmium, because the tobacco plant absorbs the metal. Cadmium, being chemically similar to zinc, may replace zinc in the DNA polymerase, which plays a critical role in sperm production.