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September 29, 2010, 12:01 am Phys Ed: Are Bad Knees in Our Genes?
By GRETCHEN REYNOLDS Lewis Mulatero/Getty Images
Are fragile knees inherited? That intriguing question motivated a new study published earlier this month in The British Journal of Sports Medicine, during which researchers looked at one family’s propensity for shredding anterior cruciate ligaments during sports. The report was part of a much larger, ongoing study of risk factors for A.C.L. injury led by researchers, affiliated with the Cincinnati Children’s Hospital and Ohio State University, which involves thousands of young athletes. For this pocket version of the larger experiment, the scientists singled out a set of fraternal twin girls who already had been videotaped in the laboratory while wearing reflective markers. The angles of their knees during landing and cutting maneuvers had been analyzed, and the knees themselves measured. At the time of the taping, both girls’ knees were healthy. But within a year, each had suffered a catastrophic A.C.L. tear during separate volleyball and basketball games, as had an older sister, who wasn’t part of the original study.
“We thought this repeated incidence of A.C.L. tears within one family was important to look at,” said Timothy Hewett, Ph.D., the director of sports-medicine research for Ohio State University and Cincinnati Children’s Hospital and lead author of the new study. “In my lab, we have another set of twins, identical young women, who are post-docs. They both had torn their A.C.L.’s” as high-school athletes. “Their father, who is one of a set of triplets, also had torn his A.C.L.,” as had his two triplet brothers, Mr. Hewett said. “Those incidences,” together with the injuries to the fraternal twins, “made us wonder, How much does familial predisposition influence your risk for an A.C.L. tear?”
The answer may be quite a bit. What Hewitt and his colleagues found, when they parsed the data about the fraternal twin girls’ knees, was that each had unusually loose, flexible knee joints, or “Gumby knees,” as Mr. Hewett called them. They also angled at least one of their knees outward during landings and had narrower-than-average notches in the knee bone, where the A.C.L. attaches to the bone. Each of these conditions previously had been identified as a risk factor for an A.C.L. tear, but they hadn’t been shown to cluster within a family. “It appears that the propensity to be at high risk for an A.C.L. tear is definitely heritable,” Mr. Hewett said.
Related
Anyone with an active daughter or who follows the sports pages knows that the incidence of non-contact-related A.C.L. tears among young female athletes is high and increasing. Many strength- and balance-training programs have been developed to try to reduce the number of these A.C.L. injuries. But part of the problem with the
training programs, Mr. Hewett said, “is that they’ll only work if they reach the girls who actually are at risk,” because of how their knees are built. “Otherwise it’s like giving antibiotics to someone who
doesn’t have an infection. It won’t work.”
As a result, some of the most-engrossing recent A.C.L.-injury research has been aimed at finding at-risk knees, in part by probing the genetics of weak A.C.L.’s. In the past year, a flurry of new studies have identified several genes that seem to be closely associated with A.C.L. tears. One representative experiment, produced by scientists at the University of Cape Town in South Africa and published in June, sequenced gene segments from 129 volunteers who’d torn an A.C.L., 38 of them women, and compared them with the same gene sequences in 216 active but uninjured people (a third of them were women too). They found that the women who’d torn their A.C.L.’S were significantly more likely to share a specific variation in one of their genes. The gene is known to affect the suppleness of collagen or connective tissue in tendons like the A.C.L. Most of the men in both groups and the uninjured women didn’t have that genetic variant. Similarly, in another experiment by the same group of scientists, published last November, a separate gene variant was found to be more common in women who’d ruptured their A.C.L.’s. That gene variant also affects the makeup of the collagen in tendons. No one knows yet whether women who carry both variants of the genes might be at especially high risk of an A.C.L. rupture.
But the emerging genetics of A.C.L. injury do raise the possibility that “in the not-so-distant future we might be able to screen” the DNA of young athletes and find those at highest injury risk, Mr. Hewett said. Obviously, he added, much work remains to be done in the field. The genetic variants so far associated with A.C.L.-injury risk have been found primarily in injured women. But men pop their A.C.L.’s, in higher raw numbers than women, since so many more men participate in sports that threaten knees (soccer, basketball and skiing, for instance). Are there genetic risk factors for men? Should all young athletes be screened, if and when a viable screening test becomes available? And given that no A.C.L.-injury-prevention program has yet proved wholly successful, what advice do you give a young woman athlete whose genetic test shows that her knee is extremely vulnerable?
“There’s so much we still have to learn and think about,” Mr. Hewett said.
For now, the takeaway from the current research is simple. Look to your family. “If you have a first-generation relative, a sibling or parent, who has torn an A.C.L., you are likely to be at above-average risk,” Mr. Hewett said, and might want to investigate the availability of A.C.L.-injury-prevention programs in your area. You also can find D.I.Y. programs online at a number of websites and on YouTube. Genetics will, of course, never provide “all of the answers to the question of why” some people tear an A.C.L. and others in the same situation do not, Mr. Hewett said. “But this field does give us another piece of the puzzle.”
By GRETCHEN REYNOLDS Lewis Mulatero/Getty Images
Are fragile knees inherited? That intriguing question motivated a new study published earlier this month in The British Journal of Sports Medicine, during which researchers looked at one family’s propensity for shredding anterior cruciate ligaments during sports. The report was part of a much larger, ongoing study of risk factors for A.C.L. injury led by researchers, affiliated with the Cincinnati Children’s Hospital and Ohio State University, which involves thousands of young athletes. For this pocket version of the larger experiment, the scientists singled out a set of fraternal twin girls who already had been videotaped in the laboratory while wearing reflective markers. The angles of their knees during landing and cutting maneuvers had been analyzed, and the knees themselves measured. At the time of the taping, both girls’ knees were healthy. But within a year, each had suffered a catastrophic A.C.L. tear during separate volleyball and basketball games, as had an older sister, who wasn’t part of the original study.
“We thought this repeated incidence of A.C.L. tears within one family was important to look at,” said Timothy Hewett, Ph.D., the director of sports-medicine research for Ohio State University and Cincinnati Children’s Hospital and lead author of the new study. “In my lab, we have another set of twins, identical young women, who are post-docs. They both had torn their A.C.L.’s” as high-school athletes. “Their father, who is one of a set of triplets, also had torn his A.C.L.,” as had his two triplet brothers, Mr. Hewett said. “Those incidences,” together with the injuries to the fraternal twins, “made us wonder, How much does familial predisposition influence your risk for an A.C.L. tear?”
The answer may be quite a bit. What Hewitt and his colleagues found, when they parsed the data about the fraternal twin girls’ knees, was that each had unusually loose, flexible knee joints, or “Gumby knees,” as Mr. Hewett called them. They also angled at least one of their knees outward during landings and had narrower-than-average notches in the knee bone, where the A.C.L. attaches to the bone. Each of these conditions previously had been identified as a risk factor for an A.C.L. tear, but they hadn’t been shown to cluster within a family. “It appears that the propensity to be at high risk for an A.C.L. tear is definitely heritable,” Mr. Hewett said.
Related
Anyone with an active daughter or who follows the sports pages knows that the incidence of non-contact-related A.C.L. tears among young female athletes is high and increasing. Many strength- and balance-training programs have been developed to try to reduce the number of these A.C.L. injuries. But part of the problem with the
training programs, Mr. Hewett said, “is that they’ll only work if they reach the girls who actually are at risk,” because of how their knees are built. “Otherwise it’s like giving antibiotics to someone who
doesn’t have an infection. It won’t work.”
As a result, some of the most-engrossing recent A.C.L.-injury research has been aimed at finding at-risk knees, in part by probing the genetics of weak A.C.L.’s. In the past year, a flurry of new studies have identified several genes that seem to be closely associated with A.C.L. tears. One representative experiment, produced by scientists at the University of Cape Town in South Africa and published in June, sequenced gene segments from 129 volunteers who’d torn an A.C.L., 38 of them women, and compared them with the same gene sequences in 216 active but uninjured people (a third of them were women too). They found that the women who’d torn their A.C.L.’S were significantly more likely to share a specific variation in one of their genes. The gene is known to affect the suppleness of collagen or connective tissue in tendons like the A.C.L. Most of the men in both groups and the uninjured women didn’t have that genetic variant. Similarly, in another experiment by the same group of scientists, published last November, a separate gene variant was found to be more common in women who’d ruptured their A.C.L.’s. That gene variant also affects the makeup of the collagen in tendons. No one knows yet whether women who carry both variants of the genes might be at especially high risk of an A.C.L. rupture.
But the emerging genetics of A.C.L. injury do raise the possibility that “in the not-so-distant future we might be able to screen” the DNA of young athletes and find those at highest injury risk, Mr. Hewett said. Obviously, he added, much work remains to be done in the field. The genetic variants so far associated with A.C.L.-injury risk have been found primarily in injured women. But men pop their A.C.L.’s, in higher raw numbers than women, since so many more men participate in sports that threaten knees (soccer, basketball and skiing, for instance). Are there genetic risk factors for men? Should all young athletes be screened, if and when a viable screening test becomes available? And given that no A.C.L.-injury-prevention program has yet proved wholly successful, what advice do you give a young woman athlete whose genetic test shows that her knee is extremely vulnerable?
“There’s so much we still have to learn and think about,” Mr. Hewett said.
For now, the takeaway from the current research is simple. Look to your family. “If you have a first-generation relative, a sibling or parent, who has torn an A.C.L., you are likely to be at above-average risk,” Mr. Hewett said, and might want to investigate the availability of A.C.L.-injury-prevention programs in your area. You also can find D.I.Y. programs online at a number of websites and on YouTube. Genetics will, of course, never provide “all of the answers to the question of why” some people tear an A.C.L. and others in the same situation do not, Mr. Hewett said. “But this field does give us another piece of the puzzle.”
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