people with Ehlers Danlos syndrome usually die of heart issues IIRC....had a co worker who’s grandchildren all have it...
Elvis hands seem pretty flexible..especially his thumbs..in this scene from jailhouse rock
https://www.youtube.com/watch?v=O9GW6wN3vk8
I have seen people make the claim about him because of his flexibility and the way he could bend on stage to greet the girls..etc.