BBC Science The Theory of (nearly) Everything 2019

GENETICS

by ZOE CORMIER (@zoecormier)

Zoe is a freelance science journalist and

author of Sex, Drugs & Rock n Roll: the

science of hedonism.

Zoe Cormier looks at children

with three parent families

There are several techniques for creating a baby from three parents. Here are two of them...

MAKING GM BABIES

GM BABIES

4

Spindle Transfer Pronuclear Transfer

Donor egg

Nuclear

DNA

discarded

Remainder of egg

containing mitochondrial

DNA (mtDNA)

Reconstructed

egg with healthy

mtDNA fertilised

Patient’s

egg with

faulty

mtDNA

Embryo implanted

into patient

Rest of egg

discarded

Nuclear DNA

transferred

to donor egg

4

1 1

(^3) Pronuclei
discarded
Donor
egg
fertilised
Remainder
of egg
containing
mtDNA
Reconstructed egg
containing nuclear
DNA from both
parents, and mtDNA
from donor
Patient egg with faulty
mtDNA fertilised
Rest of egg
discarded
Nuclear
DNA
transferred
Donor’s male
and female
pronuclei
removed
Patient’s male
and female
pronuclei
removed
3
2
2
B
ack in February 2015, Parliament
voted to amend the 2008 Human
Fertilisation and Embryology Act
to allow ‘three-parent IVF’ for families
that carry mitochondrial diseases.
These diseases are coded
in the genes and are passed from mum
to child via the mitochondrion, the
‘battery’ of a cell.
Human egg cells contain
mitochondria the way most cells do,
but sperm cells only have them in
their tails. During fertilisation, the
head of the sperm, which contains
its genes, is inserted into the egg.
The tail of the sperm – and therefore
its mitochondria – is left behind.
This is why all of us only inherit
our mitochrondrial DNA from
our mothers.
Malfunctioning mitochondria can
produce a wide variety of illnesses for
which we have no cu re. It is estimated
that one in 200 children in the UK
carries some form of genetic mutation
that could lead to mitochondrial
disease at some point in life. Every
year, one in 6,500 babies is born with a
mitochondrial condition so severe that
they will not reach adulthood.
Altered embryos
The technique that was legalised in
the UK at the beginning of 2015 will
allow a mother to give birth to a baby
that is genetically hers, but there
will not be t he risk of it inheriting
mitochondria with dangerous
mutations. The process is known
as ‘mitochondrial donation’ or
‘mitochondrial transfer’.
A mother-to-be carrying faulty
mitochondria can opt to have her
nuclear DNA removed from her eggs
and implanted into a donor egg
carrying healthy mitochondria. The
egg is then fertilised with sperm from
the father before being implanted into
the mother’s uterus for pregnancy to
continue as usual.
On 25 July 1978, Louise Brow n –
the first test tube baby – was born in
Oldham General Hospital. At the time,
concer ns were raised about
‘Frankenbabies’ and ‘playing God’, and
some members of the public subjected
the parents to hate mail. Today,
however, more than five million
children have been born via IVF.
Ultimately, doctors are confident
that this new technique will follow in
the path of IVF to become a routine
treatment that could transform lives. 5