Uncovering the Genetics Behind Bad Backs and Dodgy Knees
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Suffering from a bad back or dodgy knees? Your parents might be to blame. A recent milestone study has uncovered which genes are responsible for the different shapes of human skeletons, from the width of the shoulders to the length of the legs. Crucially, experts have found that some anatomical ratios coded by the genes leave their bearers more prone to common musculoskeletal problems, such as arthritis or knee pain.
People with a long torso compared with their height tend to suffer from more back pain, according to scientists. Those with wider hips in relation to their height are more at risk from osteoporosis and hip pain, whereas people with lengthier thigh bones are more likely to report knee pain, arthritis in the knee and other knee issues.
“These disorders develop from biomechanical stresses on the joints over a lifetime,” said Eucharist Kun, a biochemistry researcher from the University of Texas and the lead author of the paper. “Skeletal proportions affect everything from our gait to how we sit, and it makes sense that they are risk factors in these disorders.”
The team made the breakthrough by using artificial intelligence to analyse 39,000 X-ray images of participants of the UK Biobank, who had also undergone genetic testing. The AI programme was able to pick out which genes were shaping parts of the body to create a genetic map of skeletal proportions. This process revealed 145 regions associated with genes that regulate skeletal development, only a few of which were already known.
As well as finding why some people are more at risk of musculoskeletal conditions, the study has also shed light on how human ancestors moved from knuckle-based scampering to walking on two legs - an evolutionary shift which happened around six million years ago. Humans are the only large primates to have longer legs than arms, a change in the skeletal form that is critical in enabling the ability to walk on two legs. The development of bipedal locomotion made primates more adaptable to different environments and freed their hands to make use of tools, which in turn accelerated cognitive development and set the stage for modern humans.
Researchers found that several genetic segments that controlled skeletal proportions overlapped more than was expected with areas of the genome called human accelerated regions. These are sections of the genome shared by great apes and many vertebrates but which are significantly diverged in humans, showing that the change in the skeleton was linked closely to the evolution of Homo sapiens.
“What we’re seeing is the first genomic evidence that there was selective pressure on genetic variants that affect skeletal proportions, enabling a transition from knuckle-based walking to bipedalism,” said Dr Vagheesh Narasimhan, an assistant professor of integrative biology at the University of Texas. “In some ways, we’re tackling the same question that Da Vinci wrestled with [when creating the Vitruvian Man ]. “What is the basic human form and its proportion? But we are now using modern methods and also asking how those proportions are genetically determined.”
The research, which was published in the journal Science, has uncovered the genetic basis for many common musculoskeletal disorders, as well as providing insight into human evolution. Understanding the genetic basis of skeletal proportions can help us better understand how our ancestors evolved, as well as how to prevent and treat musculoskeletal problems.
