Yes, here - you are thinking the same way I did when I read the above posts, etc.
>>Perhaps the presence/absence of Iodine had an impact on other sequencing that allowed for the chromosome to be present in otherwise healthy individuals? <<
>>Not being a geneticist by any standard, is it possible that even maladies such as Down's could be attributable to lost DNA sequencing due to an Iodine deficiency...what 'caused' the sequencing to omit the needed chromosome? <<
It's not the absence of 21, it's an extra one. From paternal or maternal, and genetic. So yes, DNA of course but then my question becomes "what" is capable of rendering such an event - this extra #21 (to equal 47 instead of 46 chromosomes - one being an extra of 21) , and typically rendered from the female side.
And then the topic of age of mother comes into the discussion as always. Yes, the incidence of Downs increases (statistically speaking) with the age of the child bearing mother. But the fact that fertility declines (and the inclusive, eg. hormonal, factors change) changes the complexion (conclusion) of these statistics quite a bit.
The few theories held thus far: genetic abnormality typically from female, age relevance (but really let's look at it as a hormonal issue for the sake of progess to any theory), and environmental factors (I think). Now we begin to see something that might correlate to Iodine deficiency.