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From: avi@pegasus.UUCP (Avi E. Gross)
Newsgroups: net.followup
Subject: Re: Viral infections:  Really CBW
Message-ID: <2529@pegasus.UUCP>
Date: Wed, 21-Aug-85 17:41:22 EDT
Article-I.D.: pegasus.2529
Posted: Wed Aug 21 17:41:22 1985
Date-Received: Sat, 24-Aug-85 14:01:14 EDT
References: <167@unc.unc.UUCP> <597@hou2b.UUCP>
Reply-To: avi@pegasus.UUCP (60545451-Avi E. Gross;LZ 3C-314;201-576-6241)
Followup-To: net.med
Organization: AT&T Information Systems, Lincroft NJ
Lines: 60
Summary: Tay-Sachs gene is here to stay

In article <597@hou2b.UUCP> halle@hou2b.UUCP (J.HALLE) writes:
>Re  Tay-Sachs...
>Virtually all Tay-Sachs births in the US today are to non-Jewish
>parents.  (Statistic from the Tay-Sachs Research Center, or whatever
>it's called.)  Why?  Those at highest risk get screening, so they
>do not conceive a potential TS baby.  Those at lower risk do not
>worry themselves about it, so do not get screened.  In about a
>generation or so, expect Tay-Sachs to be essentially erradicated
>among Jews, but prevalent among others.

I agree with the rest of the article, but there is an error in the above
submission. The frequency of the Tay-Sachs gene (you need two copies of the
defective gene to have the illness, one to be a carrier) is likely to stay
at almost the same levels in all populations. Roughly one in 30 Ashkenazic
Jews and one in 300 Sephardi Jews (a genetically distinct group for many
centuries) and one in 300 non-jews bears a single defective copy of the
gene. No live person beyond the age of five bears two copies.

One of 900 random marriages between Orthodox Ashkenazic Jews has the
potential of producing a child with Tay-Sachs. Of every four children, one
will not carry the gene, two will be carriers, and the fourth one is born
with a death sentence. 58 of the remaining marriages will have one partner
who is a carrier, and half of their children will be carriers. The other 941
marriages will produce non-carriers only.

I had myself tested years ago, and know I am not a carrier. Therefore, my
wife did not need to be tested, and no test for Tay-Sachs was done when the
amniocentesis was done on my daughter, Samantha. If a couple at risk chooses
amniocentesis, they can abort -- but this does not do anything to the number
of people who have Tay-Sachs in their genes, since the child would have died
without passing the gene on. Only if they choose not to have children in the
first place, will they avoid passing it on.

If the couple does not believe in abortion (as many do), then they are not
likely to bother with testing, and again the genetic distribution in the
population is not affected. I suspect that J.Halle meant that the number of
Jewish-born Tay-Sachs children would approach zero -- not that the gene
would disappear. Now that some of the closely-knit conditions in the
European Shtetl have largely disappeared, more marriages are with Sephardic
Jews (several of my cousins) and non-jews (several other cousins).
Paradoxically, this could actually increase the frequency of the gene, since
fewer marriages would have a chance of wasting the gene on someone who will
die!

I didn't mean to belabor the point, but there are literally hundreds of
well-studied genetic diseases that are localized to inbred-populations that
happen to be limited to Ashkenazic or Sephardic Jews or both. It is a
fascinating topic (from a biochemical/medical) view as well and one of the
few things I paid any attention to in medical school. I apologize for
getting a bit pedantic about it.

One interesting sidelight is that Jews (as a whole) can be shown genetically
to be quite diverse, and not a "race". I am still puzzled how anybody can
refer to orientals, blacks and others as being of a different "race", when
we can clearly interbreed. Perhaps they would just prefer that we didn't! I
wonder if some of the creationists in net.originds would now jump in and
tell me that actually orientals and blacks are just different "kinds" :-)
-- 
-=> Avi E. Gross @ AT&T Information Systems Laboratories (201) 576-6241
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