Sperm DNA Fragmentation At A Glance

There are many factors that contribute to the increasing incidences of male infertility, one of them being sperm DNA fragmentation. This condition damages sperm DNA and is associated with adverse effects on the process of fertilization in males. ¹

Let us delve further and understand more about this anomaly.

What Is Sperm DNA fragmentation?

As the term itself suggests, DNA fragmentation is defined as the breaking of one’s sperm DNA into separate (fragmented) pieces. It is one of the most common DNA abnormalities observed in male gametes. Sperm DNA fragmentation is known to be linked with low fertilization rates, poor quality semen, reduced success in assisted reproduction procedures as well as impaired development of embryo after a pregnancy is achieved.²

Sperm DNA Fragmentation & Its Impact On The Reproduction Process

According to WHO, sperm motility, morphology, concentration, and semen volume are the most significant parameters when it comes to analysing the former’s quality. ³ Although DNA fragmentation is a less tested parameter, sperm damage as a result of its fragmented DNA is very common. 

In fact, too much fragmented DNA in sperm has been observed to have a negative impact on implantation, development of the embryo, as well as pregnancies (both natural and assisted). This is because your body cannot repair the damage caused by DNA fragmentation, and as a result, it accumulates.⁴ 

When the level of sperm DNA fragmentation goes beyond a certain threshold, it leads to fertility problems and reduces one’s chance of conceiving naturally as well as via assisted reproductive techniques like IVF (In Vitro Fertilization).⁴

You must already know that the genetic makeup of a newborn is a result of fusion of the DNA information in a male’s sperm and a female's egg or oocyte. However, any type of damage or abnormalities in the DNA of the male or female gamete can interrupt the process of reproduction.³

Among males, sperm DNA fragmentation is one of the most common types of defect in the DNA  to be transmitted to their offsprings. Although it’s normal to have some degree of fragmented DNA in one’s sperm, when the level of fragmentation goes beyond a certain threshold, male fertility problems tend to occur. Thus, this is how sperm DNA fragmentation is found widely among both sub fertile (failure to achieve pregnancy even after 12 months of unprotected intercourse) as well as infertile men.³

Measuring Sperm DNA Fragmentation

DNA fragmentation is often measured via DNA fragmentation index (also known as DFI). This value is referred to as the percentage of fragmented sperm (sperm observed to have fragmented DNA) found in a semen sample. A higher DFI is directly proportional to the amount of damaged sperm in an individual’s sample.

In general, DFI of more than 30% is regarded as quite high and has less chances of achieving pregnancy naturally or via insemination. Even 20% DFI is considered to be quite high and the chances of achieving a natural pregnancy with it is substantially reduced.⁵

What Causes Sperm DNA Fragmentation?

DNA fragmentation is mostly known to be caused by 3 common triggers. They are:

• Apoptosis: Sperm apoptosis (programmed cell death of impaired sperm) helps regulate over synthesis of sperm cells and also helps in discarding abnormal cells. However, some defective sperm cells that have a normal morphology but an abnormal genetic makeup (DNA fragmentation) can still be found in male ejaculate (the white fluid - semen - discharged from the male reproductive tract). ³
• Sperm Chromatin Damage: The sperm chromatin mainly comprises a complex of DNA and nuclear proteins (forming the chromosomes). This genetic material might undergo DNA fragmentation while being packed into the extremely small sperm head during spermiogenesis (the final stage of spermatogenesis that results in the formation of matured sperm). ⁶
• Damage By Oxygen Radicals: Radiation from electromagnetic sources as well as toxins from industrial and other by-products can all produce free radicals, which, in turn, induces sperm DNA fragmentation. ⁷

Risk Factors For Sperm DNA Fragmentation 

Here are some common factors that have been associated with an increase in Sperm DNA fragmentation.

1. Advancing Paternal Age

Increased paternal age is linked to various reproductive issues in males. Older men are found to have lower semen volume and motility. An increased incidence of sperm DNA fragmentation has also been observed in males who are 40 and above. ⁸

2. Low Sperm Quality

Abnormalities in normal sperm morphology, low motility, and low sperm concentration have been observed to cause higher levels of sperm DNA fragmentation. ⁶

3. Clinical Factors

An increase in sperm DNA fragmentation is also observed in men with varicocele (an enlargement of veins within the scrotum), genitourinary infections, leukocytospermia (unusually high number of WBCs in semen), and testicular cancer.⁹

4. Lifestyle Factors

Obese men, as compared to normal weight or overweight men, have higher levels of sperm DNA fragmentation that might alter their sperm function and reduce fertility potential. Multiple studies have also observed that cigarette smoking and alcohol consumption can induce sperm DNA fragmentation.⁹

5. Environmental Factors

Various environmental factors such as air pollution and exposure to heavy metals (lead, cadmium), pesticides, and electromagnetic waves are also linked with increased sperm DNA fragmentation.⁹

Sperm DNA Fragmentation & Assisted Reproduction Outcomes

High DNA fragmentation has been observed to have a negative impact on the outcomes of assisted reproductive techniques like IVF (In Vitro Fertilization) and ICSI (Intracytoplasmic Sperm Injection). 

The chances of successfully carrying a pregnancy to term, growth and development of the embryo, the probability of a live birth during assisted reproduction, are all significantly lowered when the sperm is subjected to DNA fragmentation.³

Sperm DNA Fragmentation & Increased Risk Of Miscarriages

Multiple studies have linked damaged sperm DNA to early pregnancy loss and also as a potential cause of recurrent miscarriages. ^{10, 11}

In a study comprising couples who opted for IVF, more miscarriages were observed when the male partners had increased levels of sperm DNA fragmentation. The same study also concluded that there was a drop in pregnancy rate with increased incidence of sperm DNA fragmentation among the patients.⁷

Conclusion

Men who are sub fertile or infertile should be educated and guided on their chances of having fragmented DNA in their sperm. In many instances, men with normal sperm parameters have fragmented DNA. ² Thus, irrespective of the results of a classic semen analysis, males experiencing repeated reproductive failure with their spouses must also undergo sperm DNA fragmentation tests. This will help them get a clear cut picture on the root cause of their inability to embrace parenthood.

Meanwhile, men at risk of sperm DNA fragmentation are advised to wear loose-fitting undergarments, quit smoking, eat healthy, and exercise daily to try reversing the levels of fragmented DNA in their sperm.

And if you’re looking for more information on male infertility and reproductive health, don’t forget to give our other blogs in the same category a read!