There's a dreadful genetic illness known as Tay-Sachs requiring two carriers to activate the fatal effects in a child.

Probably, in reaction to the 20th century eugenics movement and its terrible results, I seems most poskim would be against any alteration of the human genome for any reason, and probably forbid it for their communities, in the name of the sanctity of human life.

There will come a time when humanity develops the technology to edit a child's genome, and to also completely identify the key genes responsible for full-blown Tay-Sachs.

Assuming two Jewish parents desired to conceive a child using IVF from which the Tay-Sachs had been edited out along the way, would this still be forbidden?

If so, would only the parents suffer the moral consequences? Or would any Jewish child whose genome had been edited in any manner even for therapeutic purposes, no longer be considered fully Jewish (i.e. mamzer or karet) as a deterrent against such an action?

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    As currently phrased, the basis for this question is a prohibition conceived in the author's imagination ("I imagine"). It seems unreasonable to expect others to speculate about the details of an imaginary prohibition.
    – Isaac Moses
    Commented Nov 29, 2013 at 8:24
  • Coming back to this four year later, this is now a plausible reality being heavily debated for fear that people will misuse the CRISPR tech to make "designer babies." (While you're in there, can you make him with blue eyes and predisposed to being good at sports?)
    – DonielF
    Commented Aug 1, 2017 at 4:16

1 Answer 1


There's a great deal of speculation to this question, but here goes:

Therapeutic genetic engineering is not necessarily a problem for Jews. Here's a note from the late Kabbalist and physicist Rabbi Aryeh Kaplan about genetic alteration:

Jacob was able to direct spiritual energy and actually to change the genetic structure of the sheep (Bereshith Rabbah 73; Midrash Tehillim 8:6; Tanchuma B 24; Midrash HaGadol). Kabbalistic sources note that at this time, Jacob was manipulating some of the highest spiritual forces that exist (Zohar 161a, 163a; Etz Chaim, Shaar HaAkudim)

My understanding is that with today's technology, all discussions of modifying an organism's genes have been via a massive dose of virus, and that therapeutic genetic engineering has not as of yet been worth its risks to the patient.

Practically, when IVF is done today, the doctors have a few embryos to choose from (in preparation for the process, the mother-to-be is given drugs to increase her ovulation), and will do whatever tests they can to choose and implant two or so that are believed not to carry any disease. That is normal operating procedures right now.

I would very much like to believe that by the point in the future that genetic engineering technology reaches the capability you describe (if it ever does), Ashkenazic Jews will have long ago all gotten in the habit of being screened for Tay-Sachs carrier status and therefore not have two carriers marry each other. This technology (and recommendation) has been around for a few decades.

As for mamzer: Rabbi Moshe Feinstein's position was that the only way a child can become a mamzer is if it was produced by a prohibited sexual act. (E.g. if a married Jewish woman was artificially inseminated by a Jewish man who wasn't her husband, the offspring still wouldn't be a mamzer.) So I can't see this as relevant here. Note that blame has nothing to do with who the law deems a mamzer: the Torah makes it crystal-clear that we do not blame the victim of a rape (Deut. 22:26), but if a married Jewish woman is raped by a Jew other than her husband, the offspring would still be a mamzer.

As for communal sanctions, "shunning", excommunications, or whatever -- I can't fathom a situation in which the community would be privy to this sort of incredibly private information, let alone why it would be any of their business. To draw an analogy from today's technology: if a couple somehow found out they were carrying a Tay-Sachs baby, G-d forbid, Rabbi Eliezer Waldenberg of Jerusalem felt they were allowed to abort it in early stages, while Rabbi Moshe Feinstein of New York emphatically wrote that it was prohibited. Yet I could not even begin to imagine that any community would have the disgusting nerve -- no, hubris -- to think they could understand the stresses that a couple in such a hellish predicament has gone through and stand in judgment after-the-fact (not "I feel that a couple in such a situation should do otherwise", but "those people are evil for what they did") and play judge, jury, hangman. (Yes there are some tightly-knit Hassidic communities where it's very much "our way or the highway" on a whole host of issues, but I really doubt you'd find a family in that community that would follow the grand rabbi's say-so on for whom to vote and what brand of nylons women can wear, yet on bioethical questions of life-and-death would just do their own thing.)

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    "My understanding is that with today's technology, all discussions of modifying an organism's genes have been via a massive dose of virus, and that therapeutic genetic engineering has not as of yet been worth its risks to the patient."You haven't considered nanotechnology, also known as molecular engineering, which could be capable of creating the necessary splices to human chromosomes in a fertilized egg before it begins dividing. We'll have this in about 200 years at the earliest given our current pace of the state of the art in this field.
    – Aule
    Commented Nov 29, 2013 at 19:14

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