Sperm DNA fragmentation assessment: Is it really helpful?
Posted Mar 16 2011 11:46pm
All infertile couples know that the sperm plays a vitally important role in fertility. However, there's still a lot of confusion ! If we need only one sperm to fertilise an egg during ICSI, does the sperm count and motility really matter ? And if it does, how and why ?
The fact that the WHO has kept on changing the definition of what a normal sperm count just testifies to the fact that experts are as confused as patients are. This is especially true when we consider 3 contentious areas. While it's true that the sperm provides 50% of the child's DNA, can it be responsible forfailed fertilisation after ICSI ? poor qualty embryos ? miscarriages ?
In order to drill down further into when the sperm can be responsible for reproductive problems, researchers have developed sophisticated tests to analyse whether the sperm are "normal " or not. In the past, the only tests we had available were the sperm count, motility and morphology. These are admittedly crude tests, and the hope was that newer tests which could directly check the functional status of the sperm's DNA would give us more useful information. Logically, since the man's DNA contributes half of the offspring’s genetic material , it is reasonable to assume that abnormal DNA in the form of fragmented DNA ( when excessive strand breaks are present ) may lead to derangements in the reproductive process.
Let's look at some of these tests.
The tests used for the assessment of sperm DNA integrity can be distinguished into direct and indirect. Direct assays try to detect the actual DNA breaks, while indirect assays quantify the susceptibility of sperm DNA to break after an external insult, such as acid treatment. The most commonly used direct assays are; Terminal Deoxynucleotidyl Transferase-mediated Nick End Labeling (TUNEL), Single Cell Gel Electrophoresis (COMET) and In-Situ Nick Translation (NT) assay. The most common indirect assays are; Flow flow cytometric acridine orange assay, Acridine Orange test (AO), DNA Break Detection-Fluorescence In Situ Hybridization (DBD-FISH) and Sperm Chromatin Dispertion test (SCD).
The very fact that it's such a long list is a testimony to the fact that we really do not understand what the results signify in real life. For example, breaks affecting genes in “silent” areas of the genome are unlikely to have any clinical importance, but no assay can evaluate this factor yet.
The truth is that for the present, there is no differentiation between clinically significant and insignificant fragmentation. While it's true that many studies using a variety of assays have shown statistically significant differences in sperm DNA fragmentation between fertile and infertile men, remember that these refer only to the mean or median . In reality, there is extensive overlap between the values found in fertile and infertile men.
Because these tests are so new, they've not been standardised. Clear reference values have still not been established, just adding to the confusion. Just like conventional semen parameters have been proven to be disappointing at predicting the outcome of IVF, sperm DNA fragmentation has been equally disappointing in predicting pregnancy rates after standard IVF and ICSI.
If you have poor quality embryos and your test shows you have increased sperm DNA fragmentation , it's very tempting to conclude that it's the sperm DNA fragmentation which is responsible for the fragmented embryos. However, this has never been proven ; and please remember this is not necessarily cause and effect. Men with higher sperm DNA fragmentation have had completely healthy and normal babies in their bedroom !
DNA fragmentation is a new parameter for the evaluation of male factor infertility . However, just because it is new does not automatically mean it is better ! In fact, at present it just seems to add to the confusion, rather than clarify it !