Ideally, everyone would like to have a healthy child. Some birth defects and chronic diseases
are due to genetic mutations that a child inherits from its parents. Using the tools
available with IVF, it is possible to prevent genetic diseases. Stay tuned and I will explain
First, I need to briefly review some information about genetics. All living beings carry genetic
information inside their cells. In humans, most cells have a nucleus where the genetic information
is stored in structures called chromosomes. Normal healthy human beings have 23 pairs of chromosomes.
23 chromosomes were inherited from the provider of the egg and 23 from the provider of the sperm. The
chromosomes are actually long strands of DNA which are twisted and compressed so they can fit inside
the nucleus. These strands of DNA are divided into sections which have various functions.
The sections that produce proteins are called genes. Human beings have about 30,000 genes.
The smallest chromosome has about 200 genes. The largest has over 3000.
Mutations are errors in the genes which can affect their function. In some cases,
a mutation may reduce the function of the gene a little bit. In other cases,
it can completely stop the gene function. There are exceptions, but in most cases,
a person has two copies of each gene, one which came from the sperm and one which came from
the egg. A mutation is said to be dominant if only one copy is enough to produce a disease.
If two mutations are needed, one from each parent, then it is called a recessive disease.
Let's take an example. Let's say a person has one copy of a recessive mutation.
That person is said to be a carrier. Carriers usually have no symptoms of the disease. If
that person produces an embryo with another person who is a carrier for the same disease,
there is a one in four chance that the embryo will inherit the mutation
from each parent. That affected embryo will produce a child with that genetic disease.
What can you do to prevent this? First, you have to determine if you and your partner are carriers
for any genetic mutations. Remember that carriers do not have any symptoms of recessive diseases so
you wouldn’t be aware that you are a carrier. There are a number of companies that offer
testing to identify potential parents who might be carriers. This is known as genetic
carrier screening. These companies will test for a few hundred
mostly recessive genetic diseases. Not all companies test for exactly the same
mutations. The diseases are usually chosen because they are more common or more severe.
In some cases, people may be aware of a rare genetic disease which runs in their family
but is not in the panel of tests offered with the regular carrier screening.
They may have to seek out a lab which has a test for the rare disease.
If both partners are carriers for the same recessive disease, then they are candidates
for IVF with embryo testing. Testing embryos for single genetic mutations is more complicated than
just testing to see if an embryo has the correct number of chromosomes. Before an embryo can be
tested for a single genetic mutation, the genetic testing laboratory must prepare a method first,
this is called probe development. This gets pretty complicated so I won’t go into a lot
of detail here but during probe development, the genetic testing lab might ask for genetic material
from a cheek swab from each parent, their parents or sometimes from previously affected children.
The final step is to perform IVF. The eggs are retrieved and fertilized. They are grown to the
blastocyst stage and then a few cells are removed. The cells are sent to the genetic testing lab.
The results may indicate that a given embryo did not inherit the mutation.
These embryos are referred to as normals. If the embryo inherited one mutation, from either parent,
then it is called a carrier. If the embryo inherited mutations from both parents then
it is called affected. Obviously, affected embryos would be discarded. The parents may decide whether
they want to attempt pregnancy with normal embryos only or with carrier embryos as well.
One final point. It is possible to test embryos for genetic mutations
and chromosome abnormalities at the same time. This might be a good option when the
provider of the eggs is older. Those people are at greater risk for making chromosomally
abnormal embryos and can benefit from chromosome testing of the embryos.
Our Infertility TV Bottom Line is this. IVF is an amazing technology. Not only can IVF help
people to become pregnant, it can also assist in reducing the chances for having children
with serious and sometimes deadly diseases.