Ah. Turns out it's one of those Mercury things.
And they're convinced that there is no evidence of a genetic link.
While I can accept that their might be a mercury link (there is some evidence), there's a lot of strong evidence of a genetic link too. It doesn't just go away because you say it doesn't exist. Heck, if things could work like that, we could probably just be wished into being that disgusting word 'Normal'. *cringes*