Does an Undiagnosed case of ADD/ADHD count as an extenuating circumstance?

In terms of my university application, I received pretty bog standard GCSE grades 9C's and one B because of my inability to concentrate for more than 20 minutes at a time. Fast forward a year and being able to visit a clinic and gain access to medication I achieved three A's and one B in my in my AS exams.

Do you think in terms of my university application, a university would be sympathetic to my undiagnosed case of a mental disorder?

Do universities see mental disorders negatively, and does it damage your application success if you have one?