A researcher in my department specializes in disease "clusters" and environmental triggers for illnesses. He's seen a number of situations where rare diseases suddenly afflict unrelated people in the same location -- I don't know how much work he's done on thyroid diseases but I'll ask him. Anyway, what he's been finding consistently is that it's well worth investigating clusters and not dismissing them as coincidence -- as the government tried to tell your mom and her colleagues. (Interestingly, the Secret Service were thinking along similar lines when they decided it wasn't very likely that Poppy and Bar would BOTH be susceptible to thyroid conditions.)
http://www.doctorzebra.com/prez/g41.htmMy colleague's worried that some agencies are trying to blame everything on genetic predisposition rather than focusing on what kinds of things in the environment might be making matters worse. (One of his analogies is that if one out of ten people in the room is fainting because of a genetic sensitivity to poor air quality, dismissing their complaints because the other 90% haven't passed out yet is ignoring the fact there's an air quality problem!) And in the meantime, there's a subtle implication that it's somehow their fault, because of their "faulty" genes that make them get cancer, asthma, etc.
Which kind of relates to something about Bush himself -- he gets rather defensive when people ask him if he has dyslexia (as Gail Sheehy did, even though it was a reasonable question given that one of his brothers has been diagnosed). Then there was the time after the anthrax attacks when a reporter asked if he was taking antibiotics as a precaution -- Bush blurted out "I don't have anthrax", more than once I think, which wasn't really answering the question.
Other DUers have mentioned that Bush's brand of piety assumes that ailments, including addictions, are inflicted as punishment -- and if you're unwell, it's your fault ... doubly so, for not having the initiative to do things that will make yourself better. (I thought it was farfetched at first, but not after finding out that the same mindset also assumes this about poverty!) This might explain why he willingly makes use of public sympathy, but wouldn't be caught dead admitting that he actually did have a drinking problem, or needed his mom's tutoring because of a learning disability. As a result, any Democrat who questioned Bush's educational record or past indiscretions was made to look like a bully! Yet Bush has never gone to AA himself, or addressed why he had problems in school. Kind of a win-win situation there -- ironically, a lot of conservatives accuse liberals of "coddling" kids who need extra help, or addicts who are having trouble staying clean.
You make quite an important point, about how ignoring symptoms could make things worse. From what I've seen, Bush dislikes even conventional criticism ... he once collided with his own garage, after Laura tried to give him some speechmaking tips on the way back from an event. He even gets cross with longtime staff like Karen Hughes if they offer suggestions about how he could make improvements. And he nearly lost it during one of the 2000 debates when he accused Gore of questioning his morals (when the VP had asked for a policy clarification). Being told "there's something wrong with you", even by someone close, would be like a personal insult to him. I imagine it would have to get pretty bad, before he agreed to be tested for a thyroid condition, or ADD, or anything else. The link above has some info on what happened when his father was treated for thyroid problems -- Bush Sr. seemed more open-minded about discussing medical issues.