Childhood diagnosis/Adult health insurance

I was just reading an article about a toddler who was turned down for health insurance because she was too small. She's healthy and normal but very petite. This story was a kind of follow up to a story about a baby who was denied health insurance for being too big.

A few years ago Mo was denied insurance when we changed companies. I wrote to the company pointing out that Mo was adopted, that the condition was diagnosed prior to the adoption, and that they could not deny him insurance based on that conditon. They never responded but they did insure him.

This all got me thinking -- practically every kid I know is diagnosed with something or suspected to have something -- ADHD, ADD, ASD, NVLD, Blah Disorder, Blahblah Disorder, Blahblahblah Disorder.

I understand that diagnostic tools are much better now than when I was a kid. I understand the need for early intervention. I understand that a diagnosis might be a relief to some parents that are struggling to raise their kids.

But I wonder what happens when these kids grow up and try to get insurance on their own. Does their childhood diagnosis prevent that from happening?

I don't really intend this to be a conversation about insurance reform -- there are plenty of threads on those topics -- but I'm curious about any real world experience with this.

Thanks!