Sperm DNA fragmentation index (DFI)

One of my readers asked me my opinion of the sperm DNA fragmentation index or DFI. The value of any clinical test depends on a number of factors. Is the test relatively easy to perform or is it subject to exceptional end user skill and ideal test conditions? Some research lab tests don’t translate well to the clinical testing world. Does the test have good predictive value so that results can be reliably used to inform patients regarding their treatments? In other words, is there enough correlation between test results and real world pregnancy outcomes to know if test results are meaningful in predicting pregnancy outcomes with intercourse, insemination, IVF or ICSI? Even if useful, are there other factors that already dictate the most aggressive treatment plan (ICSI) regardless of the DFI result?

If ICSI is to be used,  can the test be used to select sperm for ICSI or is the test just used to describe the parameters of a population of cells, most of which will not be chosen for sperm injection? This last factor is what makes a test useful to the embryologist. My issue with another “advanced” semen analysis test,  Kruger’s strict criteria, is that although very poor test results (percent normal less than 5%) is used to drive a couple to having ICSI added to their treatment plan, it is worthless to the embryologist who will choose a sperm for ICSI that “looks good” from a much lower magnification and without any measurement of sperm head that is specific to Kruger. It’s like identifying the best fruit from a bucket at your feet (Kruger’s strict) but then taking home some fruit that lies in a bin twenty feet away (selecting sperm for ICSI).

The DNA fragmentation index is a score based on the percent of cells that have detectable sperm degradation. The value of the test is based on the idea that sperm vary in the amount of fragmentation found in the DNA stands stored in the sperm head and that having lots of sperm with lots of DNA degradation is likely to translate into poor pregnancy rates.

What causes DNA fragmentation? Some fragmentation may be due to apoptosis or cell suicide, a natural mechanism that cells use to get rid of old cells or to remove excess cells that are not needed in the final developmental plan for that tissue or organ.  But these normal mechanisms of cell removal are probably not the major factor that accounts for high levels of sperm DNA fragmentation that negatively affect reproduction.

Various environmental factors such as radiation, chemotherapy drugs, some prescribed medications, pesticides, smoking, some chemicals and high heat exposure all have been shown to negatively affect sperm DNA integrity.  Some medical conditions such as cryptorchidism (undescended testicle), cancer , varicocele, fever, advanced age and infection can also affect sperm DNA integrity. Some of these causes may indirectly raise the amount of reactive oxygen species (ROS) in the sperm’s local environment. ROS is then directly responsible for causing DNA strand breaks. Some ROS activity is required for normal gene and protein activities that are necessary in sperm production. Too much ROS is destructive. Fertile men are believed to have adequate levels of natural antioxidants to keep excess ROS in check. Varicocele (a varicose vein in the testicle) repair has also been attributed to improved DFI scores.  Some patients and clinical reports suggest that antioxidant therapy (for instance, taking vitamins like Vitamin C which have antioxidant properties) may decrease ROS levels, allowing more sperm DNA to remain intact.

The sperm chromatin structure assay (SCSA) is probably the most common clinical test used to determine a DFI score although other tests such as the Comet assay, Tunel assay and acridine orange test are routinely used in research labs. For those of you who want to know about the various techniques that can be used and a review of clinical use of the DFI , might find the paper  “Clinical aspects of sperm DNA fragmentation and male infertility“, useful and it is available for free download. Another good reference for readers interested in the details of sperm production, DNA integrity and ROS might be “Sperm chromatin structure and male fertility: biological and clinical aspects”, also available for free download.

From the  Georgetown Male Factor Infertility study, three broad categories of DFI results and fertility prognosis were derived.

  • Greater than 30% fragmentation : poor fertility prognosis
  • Between 15 and 30% fragmentation: reasonable fertility status
  • Less than 15% fragmentation: good fertility prognosis.

As it turns out, this rule of thumb is pretty reliable for predicting outcomes for intercourse and IUI. For instance, if a man has less than 15% fragmentation, AND assuming no female issues, he has an excellent chance of getting his partner pregnant with intercourse or IUI.  On the other hand, if his DFI is higher than 30%, the probability of pregnancy success with intercourse or IUI is dismal. Of course, these are probabilities, not guarantees. You are looking at a population of sperm and there is no way to know which sperm will successfully enter the egg. Ironically, sperm with DNA integrity problems don’t necessarily have any trouble entering the egg and may even fertilize the egg and create embryos. But in spite of this initial success, embryos derived from sperm with poor DNA integrity are at greater risk for failure later in the development program. The miscarriage rate observed from pregnancies where the male DFI is greater than 30% is  higher than in pregnancies where the male partner had a very low DFI score. .

DFI  scores are less useful in predicting success with IVF and especially with ICSI. Clinics have reported pregnancy outcomes that are better than expected based on DFI when ICSI is used. This is surprising because there is no way to identify individual sperm which have intact DNA by looking at them. And looking at them at relatively low magnification is still the way the embryologist selects a sperm to be injected. So these favorable results with ICSI can not be attributed to selection of better sperm. Some researchers have proposed that ICSI,  by bypassing the natural egg-sperm interactions and getting the sperm into the egg, is enough to get the ball rolling and then the egg can repair some of the DNA damage and support at least the early stages of embryo development. However, the miscarriage rate is still higher with higher DFI scores than lower DFI scores, even if ICSI is used to establish the pregnancy.

Not all clinicians are convinced that the DFI is useful for reasons that have nothing to do with the validity of the test.  It is yet another test for couples who may be emotionally (and financially) fatigued by the increasing list of diagnostic tests offered to both male and female. In many ART programs, ICSI is already the “go to” solution for any number of infertility diagnoses so another test to direct the clinician to use ICSI is not really useful. Some clinicians use ICSI for any history of male infertility without an obvious cause, in recognition of the fact that molecular problems are not detectable by routine semen analysis. DFI scores are probably most useful to decide whether there is a reasonable expectation of pregnancy with intercourse or insemination and thus may be more useful to the primary doctor or OBGyn who may do some preliminary infertility diagnosis and treatment, rather than the REI whose treatment plan will more quickly include more aggressive treatments like IVF and ICSI.

So what is my opinion of DFI? I think it may be a useful test for some clinicians, especially when they are trying to decide between intercourse or IUI and more aggressive treatments. For the embryologist, once ICSI is ordered, the DFI index does not help the embryologist select the best sperm and so has no value for the embryologist.

 

© 2011, Fertility Lab Insider. All rights reserved.

©2011 Fertility Lab Insider. All Rights Reserved.

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