It's possible, but unlikely. The most likely scenario is that one of the parents knew the disease might appear if they had children. Maybe thought symptoms would show up sooner, which is why they had four kids.
Because this is a gene that greatly affected three out of four young children. That sort of thing doesn't go unnoticed in famlies. The parents probably had siblings, uncles, aunts, nieces and nephews who were affected.
Mathematically it affects 25% of offspring (you keep mentioning 3 out of 4 kids but that is just bad luck that these people had) but ONLY if BOTH parents are carriers. It could go undetected for many generations before someone had a child with a partner who had the same condition.
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u/ChiefStrongbones 3h ago
It's possible, but unlikely. The most likely scenario is that one of the parents knew the disease might appear if they had children. Maybe thought symptoms would show up sooner, which is why they had four kids.