DNA fragmentation in sperm: TUNEL
When a couple fails to get pregnant or has an unsuccessful pregnancy, a number of tests performed on both partners is recommended. One of the basic tests in analysis of the male partner involves performing a seminogram or spermiogram that provides us with an initial indication of semen quality. This information can be supplemented with a sperm DNA fragmentation analysis, should this be considered necessary.
The DNA fragmentation test is a technique that supplements a study of the male factor in certain cases.
The test measures the status of DNA in spermatozoa. This DNA is located in the sperm head and forms the person’s genetic makeup. In certain circumstances, this DNA can be fragmented and, as such, can lead to implantation failure, abnormal embryo development or pregnancy loss during a later stage of pregnancy.
There are different techniques for assessing sperm DNA integrity. These include the TUNEL test (Terminal Transferase dUTP Nick End Labeling), the sperm chromatim structure assay test, the comet assay and the sperm chromatin dispersion test (SCD).
Depending on the extent and type of fragmentation, and on oocyte quality (a factor that has a direct link to the female partner’s age), these lesions can be repaired by the oocyte that has been fertilised by the spermatozoon. The fact that the oocyte’s ability to make repairs decreases with age and the sperm DNA fragmentation rate can increase with age might explain, in part, the significant decrease in pregnancy rates observed in couples of an advanced age.
When the degree of fragmentation is elevated, administration of oral antioxidants can bring it down in some cases. In cases where decreasing the extent of fragmentation is not possible despite antioxidant treatment, the option of obtaining spermatozoa directly from the testicle can be contemplated. The explanation for this is that fragmentation is lower here than in spermatozoa obtained from ejaculate.
There are many factors that cause damage of this kind in DNA:
- Inefficient selection and elimination of damaged spermatozoa.
- Failures during spermatozoa maturation at an epididymis level.
- Exposure to chemotherapy, radiotherapy or environmental toxic substances.
- Periods of high body temperatures or exposure to high temperatures.
- Exposure to free radicals both at a testicular level (in the case of severe or chronic inflammation) and at a post-testicular level.
The information provided above leads us to the conclusion that when presented with cases of sterility that have an unknown cause (after having ruled out a female pathology), recurrent pregnancy loss after assisted reproduction treatment due to fertilisation failure, implantation failure or poor embryo quality or recurrent pregnancy loss, performing a sperm DNA fragmentation test, along with other tests to determine the causes behind the difficulties achieving a successful pregnancy, could prove helpful.