This is a total shot in the dark, but have you and/or your docs ever considered a non-genetic type of Ataxia at play? The fact that it's something autoimmune with encephalitis, high fever, Marfan's Syndrome, breathing difficulties, etc. are some of the symptoms that triggered this thought....How are your walking, speech, balance and coordination? Are your symptoms progressive?

As I said before, it's a pretty fat chance -- but it warrants consideration (inquiry to the doc for his/her thoughts, anyway). There are a handful of non-genetic Ataxias out there -- and autoimmune is definitely worthy of further investigation. FYI -- There's a really great pamphlet available, written especially for doctors, entitled "Evaluation and Management of Ataxic Disorders: An Overview for Physicians," which is available through the National Ataxia Foundation. It's a great tool for the doctor, especially because the field of ataxic research is relatively unknown to many doctors (older ones), mainly because of its rareity.

Just a thought...