It’s also a little hard to call it a debilitating disorder if 10% of people have it. Pale skin puts you at risk of sunburn, but it’s not considered a skin disorder. Why? I’ll leave it to the reader.
As a pale person, I can fill everyone in: it's because I can wear clothing, and since it's a social norm, it's not debilitating in the slightest bit whatsoever.
Sun burns are a lot nicer than ADHD. I can manage my day with a sunburn. I can prevent sun burns. I can’t apply lotion to stop ADHD.