The DNA of sperm supplies half of the genetic material for a baby, if the sperm manages to fertilize an egg. Damaged DNA can be a cause of infertility and also of problems with the fetus. There may be environmental causes of damage to sperm DNA, like chemotherapy drugs or the use of cigarettes. Infections, hormonal imbalances and advancing age can also adversely affect sperm DNA quality.
Healthy, fertile men can produce a small amount of sperm with genetic damage along with normal sperm. When most, or all of the sperm have genetic problems, then fertility issues arise. These sperm may not be able to properly fertilize an egg at all. Sometimes, the sperm that do fertilize an egg can produce a damaged embryo. The pregnancy may then miscarry, or if the woman carries the baby to term, the baby may have medical problems that stem from the sperm DNA issues.
Male fertility problems may arise from sperm DNA damage from environmental causes. If the man smokes cigarettes, for example, he is more likely to develop genetic problems in his sperm than if he is a non-smoker. Pollution in the air can also result in sperm DNA damage, as can contact with certain pesticides.
Drugs that target cancer cells place men at high risk for genetic damage. The sperm are more susceptible to chemotherapeutic drugs than other cells in the body as they exhibit the same type of proliferation as cancerous cells do. Radiation therapy is another medical treatment that can mutate DNA in the sperm cells. Sperm damage from these treatments can last a long time, if the cells in the testes that produce the sperm have been mutated.
Age also appears to have an effect on sperm DNA quality. In normal, healthy men, the testes destroy sperm that exhibits DNA damage. This quality control process typically becomes less efficient as the man gets older. If a man has an abnormal level of hormones such as testosterone, this can also reduce sperm DNA quality.
Infections can also produce sperm with DNA damage. Sometimes an infection inflames the reproductive tract and thereby exposes the sperm to more reactive oxygen species (ROS), highly interactive molecules that can have a detrimental effect on DNA. These ROS are also present in high numbers in men who have enlargement of the veins in the scrotum, a condition called varicocele.
Sperm require a cool environment compared to the rest of the body. This is why the testicles are outside of the body. When a man suffers from an illness that produces a feverish high temperature, his sperm can become damaged. He can also adversely affect his sperm quality if he takes hot baths, drives a lot or does anything else that heats up his testicles, like holding a laptop on his lap.