RUSSIAN biologist Denis Rebrikov
has told New Scientist that he still
plans to use CRISPR gene editing
to prevent children inheriting
deafness, despite a major
international report saying it isn’t
yet safe enough to try in people.
“We are still planning to
correct the inherited hearing
loss mutation in [the gene] GJB2,
so that a hearing baby is born to
a deaf couple,” says Rebrikov, who
is at Pirogov Medical University
in Moscow.
Three children whose
genomes were edited using
CRISPR were born in China in
2018 and 2019. The unauthorised
creation of those embryos caused
global concern and spurred
scientific institutes to set up
the International Commission
on the Clinical Use of Human
Germline Genome Editing, a
group of 18 doctors, biologists
and ethicists tasked with drawing
up guidelines for how to proceed
in a responsible way.
The main conclusion of its
report, published on 3 September,
is that genome editing isn’t
ready to use on human embryos
before implantation in the
uterus. “The criteria for safe and
effective heritable human gene
editing have not yet been met,”
says Haoyi Wang at the Chinese
Academy of Sciences, who is on
the commission.
The reason is that existing
methods can cause unintended
genetic mutations and also may
not correct the condition-causing
mutation in every cell, an issue
known as mosaicism. However,
the technology is advancing so
fast that it might be ready for use
in just a few years, says Wang.These problems aren’t a deal-
breaker for using CRISPR to treat
conditions such as cancer or sickle
cell disease, as the potential
benefits outweigh the risks, and
the changes CRISPR makes in
these cases aren’t heritable. Many
trials are already under way.However, there is widespread
agreement that it isn’t yet safe
enough to use CRISPR to make
heritable changes by editing
human embryos – with Rebrikov
being one of the few exceptions.
He told New Scientist last year
that he plans to use to CRISPR to
correct a recessive mutation in the
GJB2 gene that causes deafness.
Almost all genetic conditions
can be prevented by screening IVF
embryos before implanting them,
known as preimplantation geneticdiagnosis, or PGD. When both
parents are deaf because of a
GJB2 mutation, however, all their
children will be deaf too; PGD isn’t
an option.
When asked to comment on
the commission’s report, Rebrikov
confirmed that he still plans to
go ahead. He didn’t mention
the safety issue. It isn’t clear if
Rebrikov has any official approval
for his plans. In October 2019, the
Russian health ministry said it
would be premature to gene-edit
human embryos. But, as in many
other countries, there are no laws
explicitly banning it.
Even if CRISPR genome editing
becomes safe and effective enough
for altering human embryos, its
use to prevent deafness would be
controversial. “I would not be
supportive of it being used first
for deafness,” says Sarah Norcross
at the Progress Educational Trust,
a UK charity to advance public
understanding of science.
The commission’s report
recommends that if any countries
decide CRISPR is safe enough to
use for making heritable changes,
it should be limited to a fewsituations. First, those in which
prospective parents have no
option for having a genetically
related child that doesn’t inherit
a condition. Second, those where
PGD is unlikely to succeed – that is,
in situations where less than 1 in 4
viable IVF embryos would be free
of the condition. Even so, the
report recommends that people
should have attempted at least one
cycle of PGD without success.
Rebrikov’s plans do meet these
criteria, but the report also says
that heritable genome editing
should initially be limited to
serious conditions caused by
a mutation in a single gene.
“My model is hereditary hearing
loss, so, this can ‘be limited toserious single-gene diseases’, I
guess,” says Rebrikov. However,
the report defines a serious single-
gene condition “as one that causes
severe morbidity or premature
death”. Many would argue that
this definition excludes deafness.
While Norcross doesn’t support
Rebrikov’s stance, she and others
are critical of the report’s
recommendations for initial
uses. “It does seem rather narrow,”
she says. For instance, Norcross
doesn’t agree that people should
have already tried PGD at least
once. “PGD is not easy, and it’s
not necessarily available,” she says.
“The woman’s age does not stop
while all this is going on.”
Nor does Norcross think the
initial uses need to be limited to
single-gene conditions. “It’s not
necessarily irresponsible to make
two edits,” she says.
Many conditions are caused by
multiple mutations, and PGD is
of little use for preventing these. ❚14 | New Scientist | 12 September 2020News
3
children with genomes altered
by CRISPR have been bornThe CRISPR-Cas9 protein (blue)
uses a guide RNA sequence
(orange) to help it cut DNA
(purple, centre) in the right placeGene editingMichael Le PageJUAN^ GAE
RT
NER/SCIENCE^ PHOTOLIBRARYCRISPR babies m ay still go ahead
Calls from an international report to limit human gene editing may go unheeded
ANDREY
RUDA
KOV/BLOOMBE
RG/GETT
Y Denis Rebrikov
wants to use
CRISPR to
prevent a
mutation that
causes
deafness