Gum Disease is a warning sign that the person's body is in ill repair.
Merely think of it as an "not so early warning indicator of overall health"."
However, in this sentence:
"The effect for most, is merely their hereditary weakness."
I would be inclined to say "their predisposition" as apposed to hereditary weakness... although both could mean essentially the same thing, a family history causing the predisposition.
Edit: What I meant by family history is where they lived, how they ate, etc... NOT DNA.