It's more complex than that.
There are multiple kinds of EDS, and only one of them has a diagnosis related to joint hypermobility. For that one, there are several points they check, and one must have a given number of those (like fibromyalgia--there are multiple trigger points but at some point doctors agreed on 18 which would be diagnostic, but one doesn't need all 18 for a diagnosis, and there are other criteria, too.)
There are actually two criteria for EDS-III, joint hypermobility type: this site uses the Beighton criteria for assessing joint hypermobility (there is also a
Brighton criteria, which is a bit confusing)
http://www.ehlersdanlosnetwork.org/hypermobility.html
Pictures for JH
here (beighton)
@
Valentijn you get a diagnostic point towards joint hypermobility for being able to put your palms on the floor without bending your knees, and another for thumb-to-forearm.
As you can see, diagnostic points for EDS joint hypermobility type also include skin criteria, IBS, OI, and bone and mouth items. (I don't see on this page how many major and how many minor criteria one has to meet, but maybe I missed something.) Not things an untrained doctor would necessarily think to connect, though they are all related to connective tissue.
The other trouble is that these diseases can exist in various severity states from very mild (one notices joint hypermobility or something like that, but isn't ill) to severe (one is constantly very ill with lots of symptoms similar to ME, may get frequent fractures and other complications) to very severe (one dies of blood vessel problems from one type).
And the various types of EDS can even overlap (one might have one type with features of another type).
It is caused by a collagen deficiency. There are various molecules of collagen (if I remember right), and they should be put together in a triple helix (basically a sort of a microscopic braid of discountinous strands), but mutations causing defects can exist in various places along the strands of collagen.
Protein function is based on shape and on the chemical properties in certain places. If you change the shape (due to a mutation) or the chemical properties (say something has a positive charge when it should have a negative one), it won't fit together right with the other proteins.
So then the collagen "braid" doesn't fit together, but depending on how many changes, where the change is located, how many strands are affected, and maybe which part of connective tissue that type of collagen goes to, you'll get problems of different types and severity.
The genes have been discovered for some types, like vascular EDS (the scary one), but not for other types (of course not for joint hypermobility EDS, because anything more likely in people with ME would always be hard, right?), which might be [my speculation, unless I forgot hearing about this] from having multiple genes involved (makes it harder to find, I think).
Unusual body proportions do go with some connective tissue diseases (e.g. Marfan syndrome), but you'd need a geneticist who specializes in those, to examine you and tell you what one, if any. They'll measure things with a measuring tape to calculate ratios.