The era of designer babies may be closer than most people think, one
of Canada’s leading figures in reproductive medicine is warning.
New
techniques that test each and every chromosome in human embryos for
abnormalities, and screen for hundreds of genetic diseases, are opening
the door to a new era in assisted procreation – one that Canadians have
not even begun to grapple with, says Dr. Roger Pierson, director of the Reproductive Biology Research Unit at the University of Saskatchewan.
“We
desperately need a national think-tank on how we’re going to accept or
reject or implement the changes that are coming,” Pierson says.
Instead,
we’re still focusing on problems as old as the technology itself, he
says. “We’re still worrying about, ‘Do we disclose the identity of sperm
donors?’” Pierson says. “We haven’t caught up with the old yet, let
alone have the foresight to go into this coming world with the depth
that we need to.”
His message comes as a world pioneer in embryo screening is looking to move into the Canadian market.
Dr.
Santiago Munne – developer of the first pre-implantation genetic test
to detect Down syndrome and other chromosomal abnormalities – is
considering opening embryo-screening labs in Toronto and Montreal.
Munne, founder and director of Reprogenetics, a New Jersey-based company that has screened more than 24,000 embryos, including embryos created in Canadian fertility
clinics, since its inception in 2001, believes Montreal is a prime
market for expansion. Quebec is now paying for up to three in-vitro
fertilization treatment cycles for infertile couples – with the proviso
that just one embryo be transferred at a time in most cases. In Ontario,
an expert panel has recommended the province fund up to three cycles of
IVF, and patient groups are pushing other provinces to do the same.
“If
you have the rule that you can only have one embryo transferred then
PGD becomes more necessary because you really need to know which to
transfer,” says Munne, who will be a featured speaker next week when
Canada’s fertility doctors gather for the annual meeting of the Canadian
Fertility and Andrology Society – a meeting that is closed to the
media.
Pre-natal genetic diagnosis is designed to select
genetically “normal” embryos created through in vitro fertilization
before they are transferred into a woman’s uterus. Anomalies can be
detected in embryos only two or three days old, based on a single cell.
The
tests were originally developed for couples at high risk of
transmitting devastating hereditary diseases to their children –
diseases such as myotonic dystrophy or Tay Sachs, a progressive
neurodegenerative disease that attacks nerve cells and usually kills
children before their fifth birthday.
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Unlike older prenatal
testing, such as amniocentesis, embryo screening prevents couples from
having to discover three months or longer into a pregnancy that the
fetus is “affected”, and then face the anguish of deciding whether to
terminate the pregnancy.
With pre-implantation genetic testing, the diagnosis is made before the woman ever becomes pregnant.
It
involves in vitro fertilization, whereby eggs are retrieved from a
woman’s ovaries and fertilized with her partner’s sperm. Next, the
resulting embryos are incubated until they reach the eight-to-10-cell
stage – about three days post-fertilization. Then, one or two cells are
removed and analyzed.
Now, Munne’s lab and others are moving from
biopsying the embryos on Day 3, to Day 5, when the fertilized eggs have
reached the “blastocyst” stage and contain about 150 cells. More cells –
as many as 10 – are then plucked from the outer layer of the blastocyst
and tested – not only for single gene disorders but also for aneuploidy
– too many or too few chromosomes, the stringlike structures that carry
our genetic material.
Aneuploidy can cause several diseases,
including Down syndrome. It can also cause unexplained repeat
miscarriages, or affected embryos can fail to implant. Munne says that
70 to 93 per cent of embryos produced by women aged 35 and older are
chromosomally abnormal.
The field of PGD has evolved rapidly over
the last few years from analyzing a handful of chromosomes, to analyzing
all of them – all 23 pairs – and multiple times. “It’s much better than
what we could do in the past,” Munne says.
His lab uses a
one-step screening, called array CGH, for both genetic and chromosomal
abnormalities that allows simultaneous screening of multiple locations
along the entire length of every chromosome. “We are now testing about
25 per cent of the genome,” he says.
The combination of biopsying
embryos on Day 5 and the new screening technique has led to a
significant improvement in pregnancy rates, Munne says, by selecting out
embryos with the greatest likelihood of developing in to a baby.
Only
limited embryo screening is now being performed in Canada. Most
Canadian fertility clinics send biopsies from embryos to U.S. centres
for testing.
The risk of damage to the embryo is low, about one to
two per cent. There’s also a one to two per cent error rate, meaning
the tests miss a defect or wrongly declare a healthy embryo abnormal.
Munne says screening at his lab costs about $2,500. The results can be turned around as quickly as a few hours, if needed.
The
technology benefits couples that suffer from recurrent pregnancy loss,
meaning one miscarriage after another, Munne says. “These couples
produce a lot of chromosomally abnormal embryos.” The technology can
also be combined with the screening of any gene disorder known in the
couple. “If we know the mutation,” Munne says, “we can screen for it.”
But
virtually every disease of adulthood has an embryonic or fetal origin,
scientists are discovering – raising the prospect of one day being able
to screen embryos for early heart attack, or early-onset Alzheimer’s
disease, Pierson says.
In the future we may also be able to select
for “more refined traits,” he says, such as musical ability or
mathematic skills. Moreover, as scientists decipher the genome, learning
what different genes do, how they interact, and how to change them,
“then we start getting into much more delicate territory,” Pierson says.
“The territory is, you design what you want.”
It’s not possible now, he says. “But it’s a little closer than most people think.”
Munne rejects fears that the technology could lead to designer babies. “I don’t have any problem with perfect babies,” he said.
But
70 per cent of embryos are chromosomally abnormal, he said. Looking for
one specific gene for a “desirable trait” would reduce the odds to one
in 13 embryos, when the average couple undergoing IVF produces only
eight, he said.
In addition, most traits are not single-gene
traits, but multi-genetic, “meaning we would have to analyze many genes
just for that trait – thousands of embryos would be needed for that,”
Munne says.
Dr. Hananel Holzer, medical director of the McGill
Reproductive Centre in Montreal – which can screen nine pairs of
chromosomes and is considering expanding to all 23 – said clinics need
to be cautious about offering pre-implantation screening to patients. So
far, “there haven’t been studies that have showed that screening
increases pregnancy rates, or decreases miscarriage rates,” he said.
“You may think it’s logical – maybe it is. But we need the studies to show us.”
While
Holzer said society needs to decide on the technology’s moral
boundaries, “I think that the era of manipulating genes to create the
perfect baby is still something imaginary for now.”
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