Download Single Gene Testing

Single Gene Testing
Using Preimplantation
Genetic Diagnosis
Single gene testing using preimplantation
genetic diagnosis (PGD) is a highly
sophisticated scientific technique, whereby
embryos can be tested for the presence or
absence of a specific gene.
This allows embryos that are not affected by
a specific disorder to be selected for embryo
transfer & subsequent pregnancy.
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Since its introduction, single-gene PGD has helped hundreds of couples conceive
healthy babies. Many of these conceptions have been for couples with serious
heritable diseases in their family.
Our internationally recognised PGD program continues to lead the development of
genetic testing in Australia.
What is single-gene PGD?
Many serious genetic diseases are caused by a mutation in a single gene.
Preimplantation Genetic Diagnosis (PGD) is an option for couples where one or both
of them are carriers of such a mutation.
PGD can allow these couples to avoid passing the resulting disorder on to their
children. A few cells are removed from embryos that have been created through IVF
and these cells are tested for the presence of the mutation. In this way embryos that
are unaffected by the disease can be selected for transfer back to the woman.
This form of testing is quite different from the PGD techniques that are used to study
chromosome number (see below). At present, it is not technically possible to do a
comprehensive test for the chromosome number at the same time as single gene
testing.
Until now, testing of the embryos for single gene disorders has had to be done using
a technique called PCR. This technique involves the preparation of individual short
gene sequences for each patient to test for the presence of the mutation in the
gene. This is a very accurate technique but has the significant drawback of requiring
three to six months of preparation of the individual gene sequences.
The Virtus Health PGD laboratory that is used by IVFAustralia, has recently introduced
the new technique of Karyomapping that can replace the traditional PCR technique
for the vast majority of patients requiring PGD for single gene disorders.
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Preparation for single gene PGD
Contact IVFAustralia
Initial information on PGD process & cost estimate
Jen Cox
Public Liaison Coordinator 1800 111 483
or your local IVFAustralia Clinic
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Genetic consultation
Detailed discussion about your case
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Clinical Geneticist Dr Debra Kennedy (left)
Genetic Counsellor Dr Janan Karatas (right)
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Meet with your PGD Nurse
Collection of samples for karyomapping assessment
& preparation for IVF treatment
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PGD Nurse Karen Cain will undertake your orientation
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Karyomapping Assessment
Study of DNA swabs (parents and other family members) affected by the disorder.
Gene sequences are then compared to work up a genetic fingerprint for the
mutation that causes the diseases. Cells can then be removed from embryos to
work out which will be affected or not by the disorder, or will be carriers that could
pass it on.
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Fertility Specialist Consultation
Plan your IVF cycle
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Fertility Specialist
Fertility Specialist
A/Prof Gavin Sacks (left)
Dr Jeffrey Persson (right)
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Administration Appointment
Detailed explanation of costs of PGD testing & IVF treatment
Patient Support Team
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IVF cycle with single gene PGD
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Who should consider single gene PGD?
Patients who are at increased risk (eg 1:4) of having a child with an inherited genetic
condition (for example, Haemophilia, Thalassaemia, Cystic fibrosis).
It is important to note that single gene PGD is only possible where the exact gene
mutation, causing the problem, has been identified. There are many disorders
where, although it is apparent from the family history that the cause is genetic, the
exact gene is simply not known. In this case, single gene PGD cannot help.
As a consequence, a lot of the preparation for single-gene PGD involves detective
work by the genetics team to obtain old records and samples of DNA from family
members to track down the exact mutation and work out the genetic sequences
involved.
The essential choice that couples face in this situation are to either go through
IVF having PGD with single-gene testing or to conceive naturally and have the
pregnancy tested, then have to go through a termination of the pregnancy or to
simply accept whatever outcome happens. This is a clearly a huge decision and
it is discussed in more detail in this booklet.
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What is involved in single gene PGD?
To go through single gene PGD, a woman first has to go through an IVF cycle.
This involves her taking injections of a naturally-occurring hormone called follicle
stimulating hormone (FSH) to stimulate her ovaries to grow many more eggs than in
a normal month. She also has to take medication to ensure that these eggs are not
released before they can be collected for IVF. Sometimes this is a nasal spray and in
other cases, it may be more injections.
The eggs are then collected at a short procedure under general anaesthetic.
a technique called intracytoplasmic sperm injection (ICSI). The resulting embryos
(and not all eggs will fertilise) are grown in the laboratory for five days.
Consultation with
Consultation with clinical
geneticist & nurse to explain
costs
Egg collection
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Sperm collection
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PGD nurse
testing may
 Feasibility
include blood, genetic
& DNA testing
Consultation with your fertility
specialist to plan your IVF cycle
and sign forms
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Intracytoplasmic
sperm injection (ICSI)
 Fertilisation
 Day 3 embryo
(8 cells)
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The testing involves firstly, carefully removing one or two cells from each embryo
laboratories in Sydney. The biopsied cells are then sent to our PGD laboratory for
genetic testing.
These are tested for the at-risk genetic conditions and genetically suitable embryos
procedure that is usually similar to having a PAP smear performed.
Studies to date have shown that embryo biopsy is safe and does not affect the ability
of the tested embryo to continue normal growth and development.
 Frozen embryo transfer  Pregnancy blood test
Day 5 Biopsy 1 or 2 cells
from embryo for PGD testing
2 weeks later
 Fetal pregnancy scan at
6 weeks
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Single gene PGD testing
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What type of testing will be done?
Your individual circumstances will determine which PGD test technique is most
appropriate for your embryos, and the genetics team will discuss this with you.
Common conditions being tested for
Huntington disease (direct and exclusion)
Cystic fibrosis
Thalassaemia
Duchenne muscular dystrophy
Fragile X
Hereditary breast/ovarian cancers (BRCA1/ BRCA2)
Single gene disorders
A gene is a sequence of DNA (genetic material) on a chromosome with a particular
function (humans have up to 20,000 different genes, arranged on 23 pairs of
chromosomes). When the DNA sequence on a particular gene is altered, a genetic
disorder, such as Cystic fibrosis, may result.
Karyomapping technology
How does the new Karyomapping technology work?
DNA samples are collected, usually via a simple blood or saliva test, from the couple
as well as from other family members who are known to either carry or not carry the
gene. Preliminary testing of these samples allows the DNA fingerprint in the region of
the faulty gene to be determined. These DNA fingerprints will have a different pattern
depending on whether they have come from a sequence of DNA with two normal
genes, one faulty gene or two faulty genes.
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sperm and a few cells are removed from each embryo for DNA fingerprint analysis.
By comparing the DNA fingerprint of the embryos to the DNA fingerprint of the
family members we are able to determine, with approximately 98% accuracy, which
embryos have inherited the disease and which are free of the disorder.
What else can Karyomapping detect?
Our genetic material, or DNA, is tightly coiled into structures called chromosomes.
Every cell in an embryo should have 46 chromosomes, arranged in 23 pairs.
Sometimes embryos can have an extra or a missing chromosome. Embryos with an
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extra or a missing chromosome normally either fail to implant or lead to an early
miscarriage. Testing of the embryo for the number of chromosomes normally involves
a quite separate genetic technique.
However, sometimes the Karyomapping will be able to identify that an embryo has
an abnormal number of chromosomes and, therefore, will not be viable. However,
many chromosomal abnormalities are not apparent with Karyomapping. Just
because the Karyomapping did not detect a chromosomal abnormality does not
mean that the embryo necessarily has normal chromosomes.
Will Karyomapping be suitable for me?
All couples that are at risk of passing a single gene disorder to their children are
potentially suitable for Karyomapping. We estimate that most couples with a single
disorder will be able to have PGD with Karyomapping.
We will do an early assessment to determine if Karyomapping might be suitable for
you. This will involve an appointment with our clinical genetics team, including our
clinical geneticist, as well as consultation with the Virtus Health laboratory team.
Following this, we will need to collect a DNA sample from you and specific family
members. Analysis of these DNA samples will take 2-4 weeks and will establish
whether Karyomapping is appropriate. If this is the case, your IVF treatment can
commence almost immediately.
Patients for whom Karyomapping is not suitable will still be able to undergo PGD for
their single gene disorder but will have to use the traditional PCR methodology.
The PCR methodology requires that individual gene sequences are developed
that can be matched with the exact mutation that the parents are carrying. The
preparation of these individual gene sequences requires a further three-six months
of preparation as well as the additional costs of preparing the gene sequences.
However, if you have already paid for the karyomapping assessment, this cost will be
discounted from the total cost of preparation of the PCR gene sequences
What happens during the actual IVF cycle?
During the IVF cycle, you will receive injections of female hormone (FSH) to stimulate
your eggs to grow. You will then go through a short procedure under general
anaesthetic to collect the eggs. The eggs will taken to the IVF laboratory and will
be fertilised with your pa
laboratory for five days. On the third day of growth, a laser will be used to create
a small hole in the embryo After five days, a few cells will be obtained from each
embryo and will be sent to the PGD laboratory for testing.
Do be aware that the number of embryos that will be available for testing can be
very variable. At IVF, an average of 10 eggs may be collected of which about six
(on average) fertilise. Not all embryos grow well and an average of 2-3 embryos are
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commonly available for biopsy. However these numbers are only averages. Some
women will have more eggs and embryos than this while other women will have fewer.
Once the embryos have been biopsied, all the embryos, that are suitable for freezing
(possibly including some that have not been biopsied), will be cryo-preserved for
later transfer.
The results from the genetic testing will be available within 10 days of the biopsy
being performed. Your doctor and the genetics team will make arrangements to
meet with you to go through the results.
Once the genetic testing results are available, you can discuss the next step with
your doctor. If there is a genetically normal embryo available, your doctor can
make arrangements to have this transferred. A frozen embryo transfer cycle normally
involves a fee for the cycle. At IVFAustralia, where all the embryos have been frozen,
we will provide the first frozen embryo transfer cycle with no out-of-pocket costs for
the cycle.
Does the testing involved in preimplantation genetic diagnosis
harm the embryo?
Not as far as we know. Current research shows that the likelihood of a biopsied
embryo implanting is exactly the same as a non-biopsied embryo. Despite the need
for removal of a few cells from the embryo, there have been no reports of any health
problems as a result of embryo biopsy in children conceived after PGD.
Gender selection
Some genetic conditions affect one gender, for example haemophilia and muscular
dystrophy. Sometimes it is not possible to detect the exact genetic error that causes
the disease. However, a different genetic technique (Array PGD) can be used to
determine the gender of the embryos, and only embryos of the required gender
and with the correct number of chromosomes will be transferred.
It is very important to note that under Australian Ethical Requirements, we are only
able to provide gender selection where there is a clear medical reason for doing so.
In all other applications of PGD, we do not know the gender of the embryo.
Exclusion testing
Some people have (or have had) a parent affected by a serious genetic condition,
such as Huntington disease, that does not generally manifest until later in life. Many
people do not want to have testing to determine if they have inherited that condition
from their parent, but at the same time do not want to risk passing it on to their own
children. PGD can be used to perform exclusion testing where the genetic error itself
condition.
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What preparation is needed?
Assessment by the IVFAustralia genetics team
This is important to allow the team to investigate the exact gene that is involved in
the problem. To do this, the team will need to gather all your previous test results,
including any tests that have been carried out on other family members. They will
take a full medical history from both partners as well as obtaining a very detailed
family history. Additional DNA testing may be necessary to reach a precise diagnosis.
It is very important to bring as much information as you have to these visits.
The genetics team will spend time with you discussing your options and in particular
the difficult question of whether to pursue single gene PGD or to consider alternative
approaches as discussed below.
The length of time taken for the assessment phase will depend upon how much
genetic information is already available. Collection of samples will also be organised
for karyomapping assessment.
Review by a fertility specialist
The fertility specialist will see you to discuss what is involved in IVF, will explain this
process to you and will plan the details of your IVF cycle (which will include a
sophisticated form of IVF known as ICSI).
The IVF cycle itself
The stimulation phase of the IVF cycle will last approximately two weeks or so.
To ensure that your egg collection is synchronized with the day set for testing of
your embryos, the genetics nurse and your fertility specialist will guide you in the
preparation for your cycle.
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Do I do single gene PGD or do I conceive
naturally and test the pregnancy once it
has implanted?
This the huge decision that couples, who have been diagnosed as having
a high risk of having a child affected by a genetic disorder, have to face.
The table below sums up the pros and cons of the two approaches.
Single gene PGD
Natural conception and
testing of the pregnancy
For
For
Allows you to proceed into a
pregnancy, confident that you do not
have a child affected by the disorder
Against
The cost
Single gene PGD can be very
expensive. We will go through the
costs with you in detail.
The conception part is much easier
and more straightforward
The costs are significantly less
Against
The trauma of having to go through
a termination of a much-wanted
pregnancy
The preparation time involved
Identifying the specific genetic
problem and developing the
necessary genetic probes can take
a long time.
The uncertainty of IVF
Although most couples carrying a
single-gene disorder are fertile, IVF
remains an uncertain process.
This is all, clearly, a very personal and difficult decision indeed. Our genetics team
will spend time with you going through every aspect of this and will guide you to
the right choice for you.
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How much does PGD testing for
single-gene disorders cost?
An IVF cycle with PGD has three components of cost:
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The cost of the IVF technique
The normal costs of IVF. These include the normal fees associated with the cycle
monitoring and IVF laboratory work. Current information about this component is
available on the IVFAustralia website at www.ivf.com.au
2
The cost of the hospital stays
This includes the cost of the admissions, procedures and required anaesthetics
for the egg collection and later embryo transfer. The exact amount of this varies
depending on the hospital, the anaesthetist and whether or not you have private
health insurance.
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The cost of the PGD technology
This is shown in the accompanying sheet.
Our patient support team will be pleased to go through all of the costs that would be
involved in your IVF cycle so that you are fully informed before you make any definite
decisions to proceed.
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