MadSci Network: Genetics

Re: Using Genitic engineering/before birth/decide persons blood type

Date: Wed Nov 14 12:52:39 2001
Posted By: Doug Reed, Faculty, Toxinology & Aerobiology, USAMRIID
Area of science: Genetics
ID: 1005602200.Ge


I'll provide the *direct* answer to your question in a moment. I did look 
at website and from there I went to the definitive place to 
look - PubMed, part of the NIH's website at

I did find references from over ten years ago that "non-secretors" had a 
somewhat higher risk of autoimmune diseases, for reasons unknown then and 
still unknown. And a 1989 review article mentioned that this was 
controversial so hardly to be considered well-proven. Since nothing has 
been published since 1989 on the subject I think it proved untrue. I found 
nothing indicating that type As or type Os lean any particular way in 
their diets. I did find one reference asking if this so called "blood type 
diet" is fact or fantasy - but the article was in Norweigian so I was out 
of luck. I'm not saying it isn't factual, but there doesn't seem to be any 
evidence in the medical literature supporting it. If D'Adamo has such 
evidence then it should be published with peer review to insure the 
accuracy of the data. But I have my suspicions - most "diet gurus" are 
scam artists out to make a buck. Given the lack of publications in the 
medical literature since 1989, the assertion that "non-secretors" don't 
live a full life or have weakened immune systems I believe is nothing but 
something contrived to sell books.

But, let's suppose for a moment that there is genetic linkage between 
blood type and secretion of alkaline phosphatase. That isn't to say that 
blood type controls the secretion, it means that the two genes are very 
close to one another on your chromosomes. Genes linked on the same 
chromosome (remember, you have 22 paired chromomsomes plus 2 sex 
chromosomes) are often linked and the closer together on the chromosome 
the tighter the linkage. Through very poorly understood mechanisms, 
though, chromosomes can break and rejoin with the other chromosome that 
makes up the pair - leading to new gene arrangements. Again, the 
possibility that bloodtype and alkaline phosphatase secretion could 
be 'separated' would depend greatly on the distance between the two genes. 
So it would be better to screen for the gene controlling secretion of 
alkaline phosphatase rather than blood type.

Another thing to keep in mind is that your digestive system changes 
drastically from birth up until you become a full-fledged adult. This is 
why your taste buds change over time - things that didn't taste good as a 
kid taste good as an adult - this is a reflection of changes in your 
body's needs, the body trying to guide you in what to eat. So I see no 
value in evaluating fetal blood type to aid digestion. If true you could 
easily screen after birth and then evaluate diet as the child matures.

And finally - your question is a little vague. Are you asking whether we 
should use genetic engineering to fix the non-secretory phenotype, 
assuming that it is a problem? That technically could be done but raises 
huge moral issues. There are diseases of genetic origin that we could 
screen for and possibly could cure by genetic engineering. But this 
science is in it's infancy - not something I would trust my child's life 
with no matter how severe the potential disease. And, if the science were 
to be perfected - why stop there? Why not engineer genes that control 
obesity or cholesterol, or genes that control addiction to narcotics? 
Certainly genes associated with cancer or autoimmune diseases would also 
be high on the list. Where would we stop? Once we've done all that, why 
not let the person choose the gender, the eye color, the hair color, the 
height, etc...?

Here's the rip - those genes exist for a reason, and that reason is that 
it confers some evolutionary advantage even if we can't necessarily see 
it. For example, the gene that causes sickle cell anemia in Africans. When 
a child gets both copies of that gene the resulting illness is deadly. So 
why did this gene arise, and why is it still in the gene pool? Simple - 
scientists found that people with one copy of the gene were resistant to 
infection by malaria. So they were less likely to die from malaria but 
there was a one in four chance that one of their children would have 
sickle cell anemia.

Again - the moral issue is the bugger and how you answer it probably 
depends greatly on whether you are someone who suffers from, or knows 
someone who suffers from, a debilitating disease with a genetic cause. But 
keep in mind that tampering with our genes is tampering with nature and 
the consequences could be dire for our species.

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