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What is sperm DNA fragmentation?


Up to 50% of infertility cases are due to the male factor. Sperm health is key to increasing the chances of conception, therefore it is important to get the sperm tested to see if there are any problems. However, while a standard sperm analysis would look at various factors that affect sperm quality, such as sperm count, motility and the shape of sperm cells, they often don’t look at the DNA of the sperm themselves.

What is DNA fragmentation in sperm? 

Simply put, DNA fragmentation is where the instructions contained within the nucleus of a cell break down. You could think of it as a message typed on a broken keyboard - some letters are mixed up and some don’t print at all, and therefore not all of the important information can be read. 

Damage of this type is quite common in the cells of your body, most of which have the ability to correct their own DNA. Unfortunately, mature sperm cells cannot do this, so any changes are irreversible. This change to the DNA of a sperm cell can happen at any point in its life cycle, from when it is produced in the testicles to post-ejaculation. 

When DNA fragmentation occurs in the sperm, it can be very impactful on a man’s ability to have children - whether through natural conception or a fertility treatment such as IVF.

How does DNA fragmentation affect male fertility? 

In fertilisation, the purpose of the sperm and the egg is to each provide half of the chromosomes needed for a full set. These then combine in a fertilised egg or zygote, which grows into an embryo as the pregnancy progresses. However, if the sperm’s DNA contains breaks due to DNA fragmentation, then these errors in the DNA sequence could be passed on to the zygote. 

In some cases, the egg cell has the ability to repair errors in the genetic code of the sperm. This is less likely if the damage is extensive or if the egg is weaker - for example, if it has poor egg quality

Sperm DNA fragmentation can have a range of effects, including:

  • Embryonic failure to develop or implant (difficulty conceiving)
  • Miscarriage
  • Genetic conditions in the resulting baby

However, it’s important to note that successful, healthy, full-term pregnancies have been achieved in couples where sperm DNA fragmentation is an issue, and an assortment of male fertility treatments are available that may help.

What causes DNA fragmentation in sperm?

Sperm DNA fragmentation can occur as early as spermatogenesis (the process where sperm is made). Part of the production process that goes on in the testicles involves the genetic material of the sperm cell forming inside the head of the sperm. This is a lot of material to get into a small space, therefore it coils up and doubles back on itself so it can all fit. This coiling can cause physical damage and breaks in the DNA sequence. 

DNA fragmentation may also be caused if there are issues with the mechanisms that allow the DNA to be packaged tightly into the head of the sperm. This could leave the DNA susceptible to damage even after the sperm is fully mature. 

Another possible cause of DNA fragmentation is oxidative stress. This is the name given to damage caused to cells in our bodies by free radicals, also known as reactive oxygen species (ROS). Free radicals are unstable molecules that aren’t usually a problem in low amounts. They are countered by antioxidants, which we get from food and supplements as well as naturally producing them in our bodies. 

However, oxidative stress can cause DNA fragmentation, among other issues, if there are either too many free radicals in the body or too few antioxidants. High levels of free radicals can be caused by a range of environmental factors, including: 

  • Exposure to toxins such as heavy metals, pollution or pesticides
  • Exposure to radiation
  • Illnesses and infections
  • Smoking tobacco
  • Drinking alcohol

The body has a mechanism in place to destroy faulty cells such as sperm with DNA fragmentation. This is called apoptosis, often described as a planned cell death. Essentially, your body can add a protein marker to any cells that are damaged, deformed or otherwise abnormal so that they can then be eradicated. Unfortunately, this process doesn’t have a 100% success rate, which is how DNA fragmentation can continue to be a problem. 

According to research, there appears to be some correlation between certain conditions and high levels of sperm DNA fragmentation. These include: 

  • Paternal age
  • Smoking
  • Drinking alcohol
  • Infection and illness
  • Cancer treatments such as chemotherapy and radiation exposure
  • Exposure to chemicals or toxins

There is also some evidence to suggest that men with other semen abnormalities may be more likely to have a higher sperm DNA fragmentation index. Why? Well, the cause behind this comorbidity isn’t fully known, but it’s likely that DNA fragmentation is either caused or exacerbated by the same factors that cause other semen abnormalities like poor morphology or a low sperm count.

What is a DNA fragmentation test? 

DNA fragmentation is not one of the factors assessed in a traditional semen analysis test, which means that the condition could fly under the radar while you continue to struggle to conceive. Fortunately, there are tests available specifically for identifying sperm DNA fragmentation issues so that treatment plans can be made. There are a variety of tests available that use different techniques, but they should all aim to give you an idea of whether or not you have DNA fragmentation issues. 

Usually, a DNA fragmentation test will give you a figure known as your DNA fragmentation index or DFI. This number represents the percentage of sperm in a given sample that have DNA fragmentation issues. Although there aren’t any set parameters, it’s generally thought that a DFI higher than 30 to 50% is likely to have an impact on fertility. Fertility may also be affected in those with a DFI of 15 to 30%, especially if they have other semen problems such as low sperm count, low sperm motility, or if their partner has risk factors for infertility.