Late in the first quarter in only his third game this season, one professional football team’s star edge-rusher limped off the field, gesturing to his trainers with his thumb down. Apparently, he already knew what he’d find out a short time later with an MRI: he’d again torn his ACL, the anterior cruciate ligament.
While a hard tackle or awkward fall can tear an ACL, some people may be more prone to an ACL tear than others, and their genetics may explain why.
A new 23andMe polygenic risk score (PRS) report sheds light on that genetic connection. The report examines how a person’s genetics may impact their likelihood of experiencing an ACL tear, an injury particularly common among those involved in high-impact sports.
How Genetics May Influence ACL Tear Risk
First, it’s important to note that your genetics is only one part of the story – many other factors can influence the risk of an ACL tear.
Tears typically occur when the knee twists or extends beyond its normal range, often seen in sports that involve jumping and sudden stops, pivots, or changes in direction. That might be in sports such as football, soccer, basketball, or downhill skiing. The ACL is the most commonly injured ligament in the knee.
We also know that ACL tears are more common in female athletes. However, because more males participate in high-risk sports, the total number of ACL tears may actually be higher in males. They are also more likely in people with a family history of an ACL injury or a personal history of an ACL tear. Indeed, genetics plays an important role, with one 2020 sports medicine journal study estimating the genetic contribution to an ACL tear at approximately 69 percent.
While the exact biological mechanism involved is not yet known, the genetic associations do offer some hints. Among the many genetic variants associated with ACL tears are variants in or near genes involved in the formation of collagen, a building block for ligaments. Scientists have discovered other variants linked to tears, but most of those associations are inconclusive, and more research is needed.
23andMe’s New ACL Tear PRS Report
Knowing how genetics influences the risk for an ACL tear can empower athletes, who are at the highest risk, train smarter and work toward preventing them.
To create the new ACL Tear PRS Report* 23andMe scientists analyzed data from people who consented to participate in research to identify thousands of variants associated with ACL tears. The 23andMe scientists then created a genetic model that incorporated those variants to calculate the genetic likelihood of an ACL tear.
This PRS report, like other 23andMe PRS reports, is research-based and not validated for medical diagnostic use; it may have limitations for people with mixed or less-studied ancestries and does not account for every possible factor influencing ACL health. In addition, polygenic risk scores integrate many common variants, but they do not account for rare genetic variants or lifestyle factors that can heavily impact risk.
For individuals with an elevated genetic or family risk, creating a personalized prevention plan and scheduling regular check-ins with sports medicine professionals are great ways to keep knees healthy.
Mitigating the Risk of ACL Tears
Whether you’re a pro athlete or not, and especially if you’ve already had an ACL tear before, proper training and technique are simple ways to help lower the likelihood of injury.
Here are a few things you can do to help lower the risk of an ACL tear:
- Build muscle strength in the hamstrings, and core to stabilize the knee.
- Maintain proper technique for movements such as jumping, pivoting, and squatting — like landing on the balls of your feet with knees bent and keeping knees aligned over your toes.
- Warm up and cool down before and after physical activity to increase flexibility.
- Wear supportive, activity-appropriate footwear for correct alignment.
- Consulting with physical therapists or trainers for form and strength assessments can further reduce the risk, regardless of one’s genetic background.
We continue to learn about the role genetics plays in sports-related injuries, including ACL tears, but genetics is just one factor.
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* The 23andMe ACL Tear PRS report is based on a genetic model that includes data and insights from 23andMe consented research participants and incorporates more than 6,000 genetic variants to provide information on the likelihood of experiencing an ACL tear. The report does not describe a person’s overall likelihood, does not account for lifestyle or family history and has not been reviewed by the US Food and Drug Administration. The ACL Tear PRS report is not intended to tell you anything about your current state of health, or to be used to make medical decisions or determine any treatment.
