I'm sorry to read he's having a hard time with his brace. That is a huge thing to adjust to and of course it is natural for parents to wish their kids didn't have to do through this kind of stuff.
Many disorders are rare - much more rare than one in a thousand. If you set up as a precondition of feeling support that the people have to have been through the exact same things then yes, you may be stuck anxious alone. I would instead keep in mind that disabilities are not actually very rare and it is possible for people to receive support from others coping with disabilities and from those who are not. We've found therapists who understand the experience and challenges of life in a family affected by disabilities even though they were not familiar with the exact combination of disabilities.
One thing that might possibly help would be to avoid seeing everyone of these physical factors as separate and unlikely to occur to together. That may just add to a feeling of woe is me. In fact most of these are likely interrelated. Problems like handwriting problems, shortened hamstrings,sensory sensitivities, weak ankles and motor planning problems and preventing scoliosis are the exact sorts of reasons why consistent occupational and physical therapy including strengthening are encouraged for kids with hyptonia. I wonder if your son may actually feel more empowered to think of these various challenges as a part of having hypotonia instead of seeing each one as separate proof of the unfairness of the universe.
I recently heard a very good podcast about resiliency. You can listen online.
http://www.whyy.org/91FM/voices.html Scroll down it is the one from 12/21. It includes interviews with families who have experienced significant medical events. The program from November on cultivating gratitude is also good. There exists quite a bit of research that learning certain thinking habits can make a significant difference in the amount of pain and overall feelings of happiness even for people affected by severe pain. There are therapies that could make a significant difference.
