From: israel@unixg.ubc.ca (Robert B. Israel)
Subject: Tay-Sachs and plague
Organization: University of British Columbia, Vancouver, B.C., Canada
Date: Wed, 30 Sep 1992 21:50:19 GMT

The question (unfortunately I've lost most of the original articles)
was whether the relatively low mortality rate of Jews in the Black Death
of 1348-49 could have been due to the Tay-Sachs gene.  My original reply
was that this was unlikely because (1) I was under the impression that the
TS mutation arose much later than 1348, and (2) the gene would have to be
present at a much higher frequency than occurs now (I said it was on the
order of 1%) to have much effect on mortality.  Someone objected that the
heterozygote frequency was much higher than that.

I did a bit of reading on Tay-Sachs, and here's what I came up with.

(1) The current rate of heterozygotes among Ashkenazi Jews in the US is
around 3%.  This means a gene frequency of 1.5%, so my 1% figure was not
so far off.  Populations from some areas have been reported with up to 11%
heterozygotes.

Let's suppose that you have in 1348 a population with 11% TS carriers.
Suppose plague mortality is 50% among non-carriers (apparently in the
right ballpark for some regions, though there are no reliable statistics),
and 0 among carriers.  Then the Jewish population as a whole will have 44.5% mortality (.5 x (1 - .11)), while the general population has 50%.  I doubt
that this difference would be noticeable at the time.  

To have a noticeable effect on mortality, the frequency would have to be much higher.  You'd need to assume some mechanism (unrelated to plague, because
there wasn't any there before 1348) that could cause the frequency to 
reach such high levels.  Moreover, this mechanism would not operate in
the non-Jewish population, where presumably the mutation would arise sometimes
but did not get established. 

(2)  There are no reports of Tay-Sachs disease from before 1881.  It is
therefore conjectured that the gene frequency increased rapidly during the
last few decades of the 19th century (because it's a disease of homozygotes,
doubling the gene frequency multiplies the disease frequency by 4; at a low
gene frequency, the disease is very rare).  Resistance to tuberculosis is
one factor that is conjectured to account for this increase.  See J. Rotter 
and J. Diamond, Nature 329 (1987) 289-290.  Interestingly enough, there are
three different Tay-Sachs mutations in Jews.

gt6390a@prism.gatech.EDU (BERNSTEIN,AVRON P) wrote:

> 
> I read somewhere that there are two distinct groups that are affected
> by Tay-Sachs.  Jews of Ashkenazi descent and French Canadians (usually in
> Quebec) are the groups.  I'm not making this up at all.  If anybody has
> any info on the subject, please share it.  Are these two versions of the
> same disease or what?  Also, how can a person be tested to see if he/she
> is a Tay-Sachs carrier?

The French-Canadian disease is caused by a different mutation, and has 
nothing to do with Jewish TS.  Actually, a genealogical study seems to 
indicate that the French-Canadian mutation arose in a single individual in
the late 17th century.  The most likely candidates were a couple born in
1680 and 1683. (M. de Braekeleer, P. Hechtman, E. Andermann, F. Kaplan,
Human Genetics 89 (1) 83-87, April '92).


-- 
Robert Israel                            israel@math.ubc.ca
Department of Mathematics             or israel@unixg.ubc.ca
University of British Columbia
Vancouver, BC, Canada V6T 1Y4
Newsgroups: soc.culture.jewish