I’m guessing that there’s no one single family where every family member has a wheat allergy. I may of course now be proved wrong, but the chances of it happening must be greater than of me winning the lottery top prize.

But indulge me if you will, and work on the premise that virtually every household that contains someone with a wheat or gluten allergy, also contains someone without any problems with wheat or gluten (unless of course it’s a single occupation household).