听力课堂,开放式英语学习平台！www.TingClass.net
'Thre
e-Per
son
Babie
s'
Debat
e
Goes
Beyo
nd
Scien
ce
and
Religi
on
An embryologist at work at a fertility clinic in London.
Britain has become the first country to permit doctors to use genetic material
from three people to create human embryos. The process is called
"mitochondrial replacement therapy." But some call it making "three-person
babies."
The treatment is meant to help women avoid passing certain diseases and
disorders to their children.
Members of Britain's upper house of parliament approved the measure in a vote
on Tuesday. The lower house passed it earlier this month.
Public reaction and debate was immediate. The therapy could potentially end
several severe, sometimes deadly, health problems. But the process behind
that goal frightens many people and offends some others.
Mitochondrial replacement therapy
Here is the science of mitochondrial replacement therapy, or MRT.
A human is made from the genetic information provided by our mother and
father. Almost all our DNA is in the nucleus of our cells. That DNA is called
nuclear DNA and makes up about 99.99 percent of our genes.
学英语，练听力，上听力课堂。【免费英语听力下载】www.tingclass.net
-1-
听力课堂,开放式英语学习平台！www.TingClass.net
But about one-tenth of one percent of our DNA comes from only our mothers
and is found in organelles called mitochondria. That DNA is called
mitochondrial DNA.
Mitochondrial DNA does not create the color of your hair or the texture of your
skin. It does not make you walk like your mom or talk like your dad. The genes
that create the personal characteristics that make each of us individual are in
the nuclear DNA.
Instead, mitochondria have one major job. They use oxygen to help the body
turn food into energy. The mitochondria are like the cell's power factory.
Mitochondria gone bad
A small percentage of women have mitochondrial mutations that can be passed
on to children. These mutations cause severe diseases in an even smaller
number of those children.
Worldwide about one in 6,500 children suffers from mitochondrial disease.
Mitochondrial disease can affect all the body's systems. It can cause blindness,
hearing loss, muscle failure, developmental delays, heart defects, liver and
kidney failure and breathing problems.
The United Mitochondrial Disease Foundation says mitochondrial disease often
affects three or more of a sufferer's organs.
Mutated mitochondria do not always make children sick. But healthy girls with
such mutations still could face the problem of passing the mutations, and
possible disease, to their own children.
How mitochondrial replacement therapy works
There are two ways to replace bad mitochondrial DNA with healthy
mitochondrial DNA. The first uses unfertilized eggs from two women, the
mother and the donor.
The nucleuses of both eggs are removed. The mother's egg nucleus is then
placed in the donor's egg, which has healthy mitochondrial DNA. Then, doctors
学英语，练听力，上听力课堂。【免费英语听力下载】www.tingclass.net
-2-
听力课堂,开放式英语学习平台！www.TingClass.net
use the father's sperm to fertilize the egg. The resulting embryo is put into the
mother's womb.
The embryo contains nuclear DNA from the father and mother and
mitochondrial DNA from the donor.
The other replacement process uses a donor egg and a fertilized egg, or embryo,
from the mother. The nucleus is removed from the donor egg and replaced with
the fertilized nucleus from the mother. Again the embryo has nuclear DNA from
its parents, and mitochondrial DNA from a third person.
Human health concerns
Mitochondrial replacement therapy – MRT – is widely controversial. Religious
leaders, bioethics experts, doctors, scientists, activists, politicians and others
have entered the debate.
Many are concerned that MRT crosses what is called the germ line. The germ
line is all the genetic information that parents pass to their children. Children
born of MRT would have genetic information that is outside their germline.
But MRT does not necessarily result in just one genetically modified individual.
If the individual is female, the genetic changes would also be passed to children
born to her. That genetic alteration is permanent.
Scientists have experimented with crossing the germ line on insects and
animals. But the research is new. Scientists have known of the existence of
mitochondrial DNA for only about 50 years.
There is no way to know the long-term impact of introducing unrelated
mitochondrial DNA to human embryos until it is actually done. And, even then,
several following generations would have to be studied.
So the unknowns scare many people. Their fear should not be a surprise
considering the public's concern over genetically modified food.
Ethical concerns
People with human health concerns are joined by others offering wide ethical
and religious arguments.
学英语，练听力，上听力课堂。【免费英语听力下载】www.tingclass.net
-3-
听力课堂,开放式英语学习平台！www.TingClass.net
Critics of MRT say it is the first step onto a dangerous path of human gene
engineering. They warn of "designer babies" in the future.
For example, they fear people will use genetic technology to create babies with
certain traits, such as blue eyes, high intelligence or athletic ability.
But MRT supporters dismiss this argument. Robert Klitzman is a bioethicist and
professor of psychiatry at Columbia University in New York City. He recently
wrote an opinion piece supporting mitochondrial replacement therapy for the
"Wall Street Journal."
Mr. Klitzman says MRT cannot be fairly compared to baby design.
"I would argue that it's not, that this is equivalent to changing the batteries in
some fancy machine. The machine is the same. Sort of like getting a blood
transfusion or an organ transplant, it doesn't change the identity of the person."
Religious objections
Anglican Church officials in Britain spoke out against the measure to approve
mitochondrial replacement therapy. The Church supports some embryonic
study for the purpose of easing human suffering. But Anglican leaders say too
little is known about the part mitochondria plays in heredity. They argue that
more research must be done to guarantee the therapy is safe, ethical and
effective.
The Roman Catholic Church goes further. It strongly objects to the destruction
of embryos that can result from MRT. But it also says the process attacks the
dignity of human life.
Christa Lopicollo is Executive Director of the Department of Life Issues with the
Catholic Archdiocese of Washington.
"It threatens the dignity of the child to be seen as a product of technology rather
than a product of love, and threatens the dignity of the marriage as well by
adding an additional parent into the picture here. The Church recognizes than
an embryo, while very, very early in life, is still a unique distinct life that
deserves respect and protection."
学英语，练听力，上听力课堂。【免费英语听力下载】www.tingclass.net
-4-
听力课堂,开放式英语学习平台！www.TingClass.net
MRT interest in the US
Scientists in the United States were among the leaders in researching
mitochondrial replacement therapy. They are seeking permission to move
forward with the process in the U.S.
The U.S. Food and Drug administration held a conference on the issue a year
ago. The agency has also asked the independent Institute of Medicine to
examine the ethical and social issues connected to the treatment.
But some say the government is not moving fast enough. Susan Solomon is the
chief executive officer of the New York Stem Cell Foundation. She wrote an
editorial in "Roll Call," a newspaper covering the U.S. Congress and politics.
Ms. Solomon noted that U.S. researchers helped develop the treatment and yet
American women cannot benefit from that effort. She criticized lawmakers, the
president and federal agencies. She wrote that they had "half-ignored,
half-slighted the issue" of mitochondrial replacement therapy. Ms. Solomon
called on congress and the federal government to act now. She wrote that
debate over MRT cannot, in her words "continue delaying our ability to save
lives now."
I'm Caty Weaver.
Is it a good idea to use the genetic material from three people to create a baby
free of mitochondrial mutations? Or is science going too far in engineering
human life? We want to hear your opinions about the issue. Post your thoughts
in the comments section.
______________________________________________________
Words In This Story
organelle – n. a specialized cellular part (as a mitochondrion, lysosome, or
ribosome) that is analogous to an organ
controversial – adj. relating to or causing much discussion, disagreement, or
argument
modification – n. the act or process of changing parts of something
学英语，练听力，上听力课堂。【免费英语听力下载】www.tingclass.net
-5-
听力课堂,开放式英语学习平台！www.TingClass.net
impact – n. a powerful or major influence or effect
trait – n. a quality that makes one person or thing different from another
heredity – n. the natural process by which physical and mental qualities are
passed from a parent to a child
Caty Weaver reported this story. Kelly Jean Kelly was the editor.
学英语，练听力，上听力课堂。【免费英语听力下载】www.tingclass.net
-6-