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Factors that affect normal sperm production by the testicle (Examples: undescended testicles, cigarette or marijuana smoke, EtOH, trauma to the testicle, prior chemotherapy, a history of testicular cancer, genetic factors, genital infections, prescription drugs)
Problems with the production and maturation of sperm are the most common causes of male infertility. Sperm may be immature or abnormally shaped (teratospermia), unable to move properly (asthenospermia), or be produced in abnormally low numbers (oligospermia) or seemingly not at all (azoospermia). This problem may be caused by many different conditions including the following:
Infectious diseases or inflammatory conditions such as the mumps virus
Endocrine or hormonal disorders such as kallmann's syndrome or pituitary problem
Immunological disorders in which some men produce antibodies to their own sperm
Environmental and lifestyle factors
Genetic diseases (most are associated with sperm abnormalities, either directly or indirectly.) Indeed, up to one third of the male genome is dedicated to male reproduction thus it makes sense that many problems in sperm production and transit may be due to genetic causes:
Chromosomal abnormalities - men with an extra X sex chromosome, known as Klinefelter syndrome, often do not produce sperm or produce very low quantities of sperm; in some persons, there are the usual number of chromosomes (46) in the nucleus (center) of cells, but rearrangements in the chromosome material, where a piece of a chromosome has exchanged places with another, has taken place; men with either azoospermia or oligospermia have a higher frequency of chromosome rearrangements than is found in the general population.
Abnormal Y chromosome - in some persons, there are the usual number of chromosomes (46) in the body cells, but small sections of the Y chromosome are missing or deleted; anywhere from 3 to 30 percent of men with either azoospermia or oligospermia have deletions in the Y chromosome. This can have implications for fatherhood and the gender of the offspring. It is important to understand that men who have genetic problems which cause their infertility, such as a deletion in the Y chromosome, can pass this problem to their sons, who would also have infertility, if they elect to use their own sperm in achieving a pregnancy.