I am very hypermobile in big and small joints - my fingers and toes even bend too far back. I can plant my hands flat on the floor without much effort at all, no warm-up needed. I can sit with my feet folded on top of my legs, soles pointed up, as easily as the the "normal" way. Everything bends both directions, although certainly not as far backwards as it does frontwards!

My moms' side of the family also has long limb-to-torso ratio, my siblings and I have small jaws with large teeth and a high arch or roof. Mom's sister and brother each had aneurysms, and I've learned that one of my brothers and a first cousin also had one. (Only my Uncle's was fatal). I saw a geneticist because of all these traits, and learned I do carry a hereditary connective tissue disorder (but my heart checks out fine, thank goodness), which causes the connective tissue to be too elastic. It's a defect of a certain type of connective tissue, type II I think, which is most prevalent in ligaments, soft tissue, etc. naturally.

Can't count the number of times I've "twisted" my ankles, yet never sprained them. Have never had them looked at though, since we needed blood or bones showing, or a temp over 102 to be seen by a Dr when I was a kid.
I'm sure it played a role in how quickly muscle weakness and atrophy showed up after my injury, and why it is so hard to recover any shoulder girdle stability. I was also predisposed by a long neck (10 vertebrae above the collarbone) and a couple of scalenes that took abnormal routes through the brachial plexus. But it still took a trauma to trigger the TOS, I had no pain, numbness or other sx prior to that.

I think I have the Hypermobility form of Ehlers-Danlos as well, but the US hasn't formally accepted that category, or hadn't when I was tested. The UK is ahead of us in this field, and it's very frustrating waiting for the US to catch up.