It is easy to think that these neurological disorders are caused by environment to a great extent; and some studies show that true deprivation does cause problems in brain development that look like ADHD.
However, this kind of claim often moves over imperceptibly but surely into blaming the parents for not providing a proper environment for the child. We were once told by a well-meaning psychologist that if we were doing time-outs properly, our DS would not have the difficulties he was having (not unlike all the docs in the 1950s who blamed autism on the "refrigerator mothers"). We were "doing them properly"; they were simply not what DS needed for learning.
Our household was quite calm in my children's early days, no TV, not a lot of hustle; and yet they became neurologically interesting. Ah, well. I'm probably doing it wrong some other way.
