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How sperm DNA is damaged?

The head of a sperm contains genetic building blocks, called DNA (deoxyribonucleic acid), which are needed from the male to create an embryo with a successful pregnancy. Within the sperm head the DNA is twisted on itself and wrapped around blocks of protein known as chromatin.  Part of the role of these protein blocks is to protect the DNA from damage during the sperms’ journey from the testes to the female reproductive tract.  However, damage can still occur to the DNA and it can become fragmented. Having been manufactured without defect, the sperm may still undergo DNA damage as they reside in the epididymis waiting for ejaculation.  The main concern here is reactive oxygen species (ROS) which can react with DNA causing breaks and fragmentation.  ROS themselves can be derived from immune cells which may invade the testis during infection or inflammation or from increased scrotal temperature and smoking. It is not clear whether the DNA damage is entirely due to external factors, in some cases inherent defects in spermatogenesis may leave sperm more susceptible to DNA damage.

Normal semen analysis does not exclude sperm DNA fragmentation

Classical semen analysis is based mainly on sperm count, the number and ability of the sperm to swim and the shape or morphology of the sperm.  Testing for DNA damage in sperm is not routinely performed in a normal semen analysis. Classical semen analysis is based mainly on sperm count, the number and ability of the sperm to swim and the shape or morphology of the sperm.  Testing for DNA damage in sperm is not routinely performed in a normal semen analysis

Possible causes of sperm DNA damage:
  • Drugs, chemotherapy and radiation therapy.
  • Cigarette smoking and environmental toxins.
  • Testicular hyperthermia (use of hot baths, saunas and prolonged periods of driving).
  • Genital tract infection and inflammation.
  • Infrequent ejaculation.
  • Male’s advanced age.

The degree of DNA fragmentation correlates very highly with the inability of the sperm to initiate a birth regardless of the technology used to fertilize the egg such as insemination, IVF or ICSI. Spermatazoa with high DNA fragmentation may fertilize an egg and embryo development stops before implantation or may even initiate a pregnancy, but there is a significantly higher likelihood that it will result in miscarriage.

How to minimize sperm DNA damage and fragmentation?

The presence of ROS can be detected in semen samples, but it is not known exactly what threshold level of ROS we should regard as a threat to DNA integrity.  It is possible that increasing antioxidants in the diet, such as vitamins A, C and E may help prevent high ROS levels.  Smoking is a potent source of ROS and stopping has been shown to help semen quality in some smokers.

Overall, the advice to a man concerned about semen quality would be to eat a balanced diet containing sufficient antioxidants and to stop smoking.  Medicinal antioxidant treatments have not been shown to be effective so far, but this is one area of research that is continuing.

Sperm DNA fragmentation test

By testing for sperm DNA fragmentation, many cases of formerly “unexplained” infertility can now be explained. Many of those couples who have been previously unable to conceive with what would be considered extreme measures have been diagnosed with high sperm DNA fragmentation and treated. It is now very clear to see that having this information about the quality of the sperm can be tremendously helpful to couples and their physicians.

Read more investigation for causes of infertility