For most of my adolescent and adult life, I have been underweight. I am 6'4" and for most of that time I weighed 160 lbs. I think there is a minor correlation between Asperger's and lack of subcutaneous tissue, lax joints of the fingers,. Some, like me, have a body habitus similar to those with Marfan's syndrome, which is a connective tissue disorder. Persons with Marfan's are usually tall, with joint laxness and very little collegen or fat tissue. Most of them have ectopic lenses in their eyes due to stretched lens ligaments. For anyone with this body type, with or without Asperger's, it is good to make sure you don't have Marfan's syndrome, because persons so afflicted often die early of aortic rupture due to defective collagen. This can avoided if caught early by visualizing aortic stretching that can be seen on ultrasound. There is surgery that can correct it if found before rupture.
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Conforming to a minority is conforming nonetheless.