The relationship between ASD and EDS is actually what led to me hearing about Ehler’s-Danlos and other connective tissue disorders in the first place! Obviously research is ongoing (which is true of just about any medical condition – that’s why medicine is called a “practice”) but I found some good information here: http://www.sciencedaily.com/releases/2014/10/141010154926.htm and also here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3365276/
Then there’s this neurologist who is supposedly continuing research into the subject: http://corticalchauvinism.com/2013/08/12/ehlers-danlos-syndrome-and-autism/
I can only speak for myself, but based on my own personal experience I believe there is a high degree of credence to the theory that inflammation in the mother during pregnancy leads to the overgrowth of certain parts of the brain in the fetus that continues into infancy, and I don’t think it’s a coincidence that the area affected has been linked to both autism spectrum disorders and connective tissue disorders.
As for the other questions – pertaining to IQ and shared physical traits – I only have myself, my mother, and my sister to evaluate, but you may be onto something. My mother is highly intelligent in a non-traditional way (incredible empath, thumb so green it could produce it’s own chlorophyll) and was thought to be about 10-20 years younger than she actually was up until a couple years ago. I’m 30 and I’m regularly mistaken for a 19 year old; my sister is 6 years older than me and we’ve been asked multiple times if she’s my twin sister. I’d say we’re both above-average intelligence, and that we both exhibit some ASD traits as far as specialized areas of interest and poor social skills are concerned.
I only know one other person who has been dx’ed with EDS, and we’ve only texted, so I can’t vouch for her physical traits. I can say, though, that she is incredibly intelligent.
As to the postulation that we are commonly more anxious than neurotypicals…again, speaking only for myself, I’ve found that I’m less anxious when I’m in less pain, or in a really positive place mentally. It’s only when I start to feel as though my skin is made of wasps, or my body is trying to kill off my brain, that I start to get anxiety. Something about not feeling totally comfortable in my body makes me hyper-aware of what it’s feeling and everything else around me – that heightened awareness leads to my anxiety. Most of the time I’m really relaxed and easy-going.
Organization and perfectionism.. I just (humorously) attributed those traits to the fact that I’m a Virgo. Both definitely apply to me, though.
There’s also this blog you can check out: https://planetautismblog.wordpress.com/2014/09/11/connective-tissue-disorders-their-correlation-to-autism/ which was my first step in discovering EDS. Hope some of this long, rambling reply helps!