Body contortions sure make a great party trick, but being able to touch your thumb to your forearm or place your hands on the floor without bending your legs isn’t exactly a genetic blessing. A study published last year in the Frontiers in Psychology journal confirmed that those with hypermobile joints are more likely to suffer from anxiety.
Hypermobile joints result from variations in collagen production, a hereditary trait that causes an abnormally large range of motion. People with hypermobility—commonly known as double-jointedness— are also at a greater risk for asthma and irritable bowel syndrome.
Researchers from the University of Sussex in England found a link between joint hypermobility and anxiety disorders. In 2012, Jessica Eccles, a psychiatrist and researcher from the university, and her team used brain-imaging technology and found participants with joint hypermobility had a bigger amygdala, which is the part of the brain responsible for processing emotions like fear. During a follow-up study in 2014, Eccles' team, along with researchers from Spain, showed participants sad and angry scenes while observing activity in their brains. Hypermobile participants showed greater reactivity in brain regions associated with anxiety.
Another finding was the connection between hypermobility and a tendency to be biologically primed for panic, in a sense. As Scientific American explains, the atypical collagen production in hypermobile individuals affects the blood vessels too, and can cause an accumulation of blood in leg veins. To compensate, the heart kicks in to high gear, which "brings the entire body to the verge of a fight-or-flight reaction"—meaning those hypermobile folks are much more easily thrown into a panic.
[h/t Scientific American]