What is sperm DNA fragmentation?
Sperm DNA fragmentation is damage occurring in the genetic material of sperm. This damage is usually an alteration or a break in one of the two strands of the DNA double helix.
Several studies have shown that increased levels of DNA fragmentation are associated with decreased pregnancy and live birth rates, poor embryo quality and an increase in pregnancy loss. The Practice Committee of the American Society for Reproductive Medicine has stated that a threshold of DNA damage exists, beyond which embryo development and pregnancy are impaired [1].
Sakkas and Alvarez report that the most important causes of DNA fragmentation are abnormalities in the packaging of chromatin, oxidative stress and apoptosis. External and environmental factors that have been found to associate with increased DNA fragmentation in the sperm include heat, chemotherapeutic agents, smoking, inflammation of the genital tract and deficiency of some hormones [2].
Occurrence
A higher incidence of DNA fragmentation is observed among infertile men with abnormal sperm parameters, when compared to fertile men with normal sperm parameters. However, a small proportion of infertile men show DNA fragmentation in their sperm despite normal parameters [3, 4].
Detection
Sperm DNA fragmentation may be detected and quantified through a specialized test. Following the treatment of the sample, analysis of sperm under the microscope provides a means to distinguish between normal and spermatozoa with fragmented DNA. When the proportion of sperm with fragmented DNA is >30% the ability to fertilize is reduced regardless of the sperm parameters.
Results
The results of the DNA fragmentation test may provide answers to unexplained infertility, an indication of the method of ART that needs to be used and possible treatment that can be undertaken in order to reduce the fragmentation levels. For example, incorporation of antioxidant vitamins in the diet and cessation of smoking may reduce the proportion of abnormal spermatozoa.
- The Practice Committee of the American Society for Reproductive Medicine. 2006. The clinical utility of sperm DNA integrity testing. Fertility and Sterility. 86: S35 – S37.
- Sakkas D., Alvarez J. G. 2010. Sperm DNA fragmentation: mechanisms of origin, impact on reproductive outcome, and analysis. Fertility and Sterility. 93: 1027 – 1036.
- Saleh R.A., Agarwal A., Nelson D. R., Nada E. A., El-Tonsy M. H., Alvarez J. G., Thomas A. J. Jr, Sharma R. K. 2002. Increased sperm nuclear DNA damage in normozoospermic fertile men: a prospective study. Fertility and Sterility. 78: 313 – 318.
- Simon L., Brunborg G., Stevenson M., Lutton D., McManus J., Lewis SE. 2010. Clinical significance of sperm DNA damage in assisted reproduction outcome. Hum Reprod. 25: 1594 – 608.