Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site pegasus.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!ihnp4!pegasus!avi 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 suggested paths: [ihnp4, allegra, cbosg, ahuta, ...]!pegasus!avi