Of course they do.
But when there is a spike 4x above what is expected something is going on.
Rule out the easy questions first.
And I’d look at the environmental influences hard. That is why the doctors are sending these parents to geneticists — to rule that out.
Very true. A spike four times normal is highly unusual. It very well could be some kind of environmental factors, something in the water, etc.
Neural tube defects are also associated with a lack of folate in the diet, I would first look at regional dietary habits which may not sound as sensational as nuclear fallout but would be the “easy question.”