Sperm DNA fragmentation assessment: Is it really
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 fertilize an egg during ICSI, does the sperm count
and motility really matter? And if it does, how and why ?
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 for:
Failed fertilisation after ICSI ?
Poor qualty embryos?
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.
look at some of these tests.
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).
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.
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.
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.
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!
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!