My wife had EDS (Ehlers Danlos Syndrome), a genetic condition that results in malformed collagen -- it is too stretchy. She wasn't diagnosed until she was 35, even though in retrospect the symptoms were obvious.

She had five knee surgeries, starting at age 20, to address instability and knee pain that were not caused by any injury (nor has she ever been overweight), just standing and walking like an average person. She has no foot arch, bruises very easily, has velvety soft skin, has an unusually high arch in the roof of her mouth, and has POTS (postural orthostatic tachycardia syndrome). These are all common hallmarks of EDS, but no doctor connected the dots until the 5th surgery. BTW, none of the surgeries helped and in fact made things worse.