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Posted on October 31, 2019 at 10:44 PM

One caution when objecting to the prospect of heritable
human gene editing is to take care not to overestimate what it technically
possible.  That is, an all-too-easy
argument is that attempts to edit a disease gene will lead, by momentum if
nothing else, to “designer babies,” with children not just being
genetically selected but in fact engineered in great detail for traits like
attractiveness, athletic prowess, height, and intelligence.  This contributor to this blog has repeatedly
taken the position that heritable human gene editing is a project that
fundamentally alters the way we see ourselves and each other; that divides the
human race into “actors” and “acted upons;” that has no
prospect of prospectively assessing long-term, unintended consequences, to an
individual subject, subsequent generations, or society at large; and that
fortifies a perspective of admitting to the human race only those members we
want to admit.

Along the way, we must keep in mind that “designer
babies” are not likely to be feasible in the foreseeable future.  One recently-reported case in point is a
study by scientists at the Hebrew University of Jerusalem.  A preprint (in advance of publication in a peer-reviewed
journal, it is said) is publicly available
  I daresay the details will be
inaccessible to all but specialists in genetics, but a summary
of key points is provided by a technical writer at a website called GenomeWeb.
  In brief, some of those points:

  • A score based on assessment of multiple genes
    has previously been suggested to explain only about 5% of the difference
    between individuals in IQ (300,000 people genetically tested) or 25% in height
    (700,000 people tested).
  • These researchers tested about 1000 people, and
    considered about 15,000 genetic variations.
  • They looked at offspring of actual couples and
    also “simulated” matches for about 500 would-be couples made from
    individuals for whom they had genomic data.
  • Of note, they appear to have looked at
    “SNPs,” or “single nucleotide polymorphisms,” which are
    relatively easy to catalog across the 30,000 or so human genes, and which
    themselves run into the hundreds of thousands across those genes, but SNPs are
    far from the whole genetic story.  Larger
    differences in genes, or how those genes are translated into biological traits,
    is much more complex to assess.
  • They surmised that, if their score were used to
    try to predict height, the average gain would be about 2.5 cm (about one inch),
    with a range of 1-6 cm.  If used to
    predict IQ, the average gain would be about 2.5 points, with a range of 1-7
  • Then they also looked at 28 actual families with
    lots of kids, from 3 to 20 (!).
  • For the actual families, the score predicted to
    cause the tallest child did so for only 7 of the 28 families, and the highest
    scoring child was actually shorter than average in the family in 5 of the 28
    families.  No attempt to assess IQ for
    these real families, apparently.
  • They point out other reasons why trying to
    select for IQ might be problematic—potential association with autism and
    anorexia, for example, as well as just general complexity.
  • They suggest that for most people undergoing
    IVF, and creating fewer than 10 embryos in the process with less than 100% success
    after implantation in the womb, the odds are not good for making a reliable
    forecast of an offspring’s height or IQ.
  • They make these points without commenting more
    broadly on the ethics or policy wisdom of allowing or encouraging heritable
    genome editing to proceed.

A complex story, and a developing one, to be
sure, but one should not be too quick to accept grandiose promises for
predicting complex traits based on genetics. 
At least for now, those appear to be rather “ahead of the
puck,” shall we say.

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