Inherited dispositions, including sensitivity, to certain things is well documented.

I'd be interested to know the amount of people who realise they're suffering from amalgam illness who would also categorise themself as sensitive people, in all senses of the word. Sensitivity and awareness of illness go hand in hand really. It goes without saying; if you're more sensitive in general you're definitely going to more sensitive to heavy metals.

Whether some people are just less sensitive, have fillings that aren't leaking as much, or have immune systems that are strong enough to remove heavy metals, I'm quite sure after prolonged exposure they'll be affected. If you're sensitive you'll notice it sooner, and perhaps you'll be affect by it to a greater degree.