HDSA Genetic Testing Guidelines
- The guidelines are recommended procedures, not regulations.
- It is strongly recommended that pre and post test counseling
be incorporated in any pre-symptomatic testing program. While the
HD gene discovery alters some aspects of the test, the personal,
family and ethical issues remain unchanged and the importance of
counseling is therefore not diminished.
- The decision to take the pre-symptomatic test should always
be an informed, carefully considered and freely chosen personal
decision. Under no circumstances should an individual be coerced
- The testing program should include the following components:
- Initial telephone contact/pre-screening interview
- Three pre test, in-person sessions for genetic counseling,
neurological evaluation and psychological evaluation
- Fourth session for disclosure of results
- Post test counseling
- The participant should be accompanied to all testing sessions
by a companion (spouse, close friend, not a sibling).
- Excluding prenatal non-disclosing testing of exceptional circumstances,
there should be at least one month's interval between the pre test
sessions and the final decision to take the test.
- Minors should not be tested unless there is a medically compelling
reason to do so.
- Test results should not be divulged to anyone other than the
participant without his/her consent
- Test results should be given in person; results should never
be given over the telephone or by mail.
- Confirmatory testing may be offered to an individual with clear
symptoms of HD and a documented family history. However, a clinical
neurological examination remains the definitive means of diagnosis.
- Individuals or couples considering prenatal testing should seek
genetic counseling prior to conception.
- Laboratories are advised not to accept anonymous DNA samples
The Columbia Genetic Testing Program
Our counseling and testing program meets these needs by following
the guidelines recommended by the Huntington's Disease Society of
prior to the genetic test:
after the genetic test:
- two genetic counseling sessions
- psychiatric evaluation
- neurological examination
- at least one follow up visit after results are given
- one genetic counseling visit to discuss the results
This program involves four to six appointments. Some individuals
may need more visits to complete the testing process. We estimate that the entire testing process may take from 2-4 months, but the
time frame may vary from person to person.
I. Presymptomatic Genetic Testing
II. Confirmatory Genetic Testing
III. DNA banking
IV. Prenatal testing
V. Preimplantation Genetic
This genetic test is for individuals at risk for HD who do not have
Confirmatory genetic testing determines whether individuals showing
symptoms actually have the HD gene. Genetic testing for individuals
with symptoms may be necessary if the family history of the HD is
To diagnose HD:
- Medical history
- Family history
- Neurological examination
- Brain imaging test (MRI, CT)
- Laboratory tests
- Genetic test (if necessary)
A research roster of Huntington's Disease patients and families
was established in 1979 at Indiana University. The HD research roster
computerizes the names of families, including information about the
history of HD in the family and other related data. This information
identifies families who are interested in participating in research
The Huntington's Disease Research Roster provides an opportunity
for families to store DNA from persons who are presumed to have HD.
Storing DNA will later assist in confirming the diagnosis of HD in
For more information on DNA banking and the Huntington's Disease
Research Roster call (317) 274-5744 or email HDRoster@medgen.iupui.edu.
Family Planning and Huntington's Disease
Often families in the Huntington's Disease Center ask questions
about the risk for children to inherit the disease. Many people would
like to know about ways to prevent passing Huntington's Disease (HD)
to the next generation. Genetic testing is available to determine
whether a person has the gene that causes HD and the same test can
be used in some family planning options. There are many different
options to consider that are outlined below. We recommend genetic
counseling to explore each of these options in more detail.
What are the options for testing a pregnancy?
Prenatal testing is used to determine whether or not a fetus has
inherited the HD gene. This can be done by amniocentesis or chorionic
villus sampling (CVS).
Amniocentesis is the withdrawal of a small amount of amniotic fluid,
the fluid surrounding a developing fetus. The procedure is done in
a doctor's office or hospital clinic, usually when a woman is about
16 weeks pregnant, counting from the first day of the last menstrual
Before the procedure, the doctor performs an ultrasound scan (sonogram)
which shows a picture of the uterus, the placenta, the amniotic fluid
and the fetus on a screen. Then the doctor inserts a very thin needle
through the woman's abdomen into the uterus, and takes out an ounce
or less of amniotic fluid. This part of the procedure lasts only
a few minutes. After the sample is taken, another ultrasound check
Amniotic fluid cells, which have been shed from the fetus, can be
used to test for chromosome abnormalities and genetic diseases such
as Huntington's disease.
Chorionic Villus Sampling (CVS)
CVS is the withdrawal of a small amount of chorionic tissue. This
tissue is from the developing placenta. The chorionic villi are made
up of cells which develop from the same fertilized egg cell as the
fetus, so taking a sample of the chorionic tissue is almost the same
as taking a sample from the fetus. CVS is usually performed in a
doctor's office or hospital setting between the 10th and 12th week
of pregnancy, counting from the first day of the last menstrual period.
CVS is an earlier alternative to amniocentesis,
which is usually performed around the 16th week of pregnancy.
Preimplantation genetic diagnosis (PGD) offers an alternative to
more traditional methods of prenatal genetic testing (CVS or amniocentesis),
an allows genetic analysis to be performed on early embryos prior
to implantation and pregnancy. This method provides individuals at
risk for HD the opportunity to know that any pregnancy they achieve
will be genetically unaffected for HD. It avoids the need to determine
if they themselves carry a mutation in the HD gene and avoids the
need to terminate a genetically affected fetus.
Couples who desire preimplantation genetic diagnosis must undergo
standard in vitro fertilization (IVF). Healthy, normally
developing embryos are biopsied to remove a single cell. The removal
of this cell should not cause any birth defects. Genetic testing
of the single cell determines the number of repeats in the embryos
to determine if the embryo is at risk for Huntington's Disease. The
genetic material from the embryos is not altered by this procedure,
and no gene therapy is done. Genetically unaffected embryos for Huntington's
Disease are then implanted in the uterus or cryopreserved for future
For individuals known to carry an HD mutation, this procedure offers
the opportunity to have genetically healthy children without the
need to terminate a pregnancy. Without such a procedure, on average
50% of the children of an individual with Huntington's Disease will
also be affected.
For individuals at risk for Huntington's Disease due to their family
history who are not symptomatic and who have not had genetic testing,
this procedure offers the opportunity to have genetically healthy
children without the need to find out their own genetic status. We
call this procedure non-disclosing preimplantation genetic diagnosis
because we do not disclose to the patient the results or any of the
genetic testing so they will not know their own genetic status. To
ensure the accuracy of non-disclosing PGD, a blood sample is analyzed
from the individual at risk to determine the repeat size in the Huntington
gene. The results of this genetic testing are not disclosed to the
patient and are only used by the laboratory performing the PGD. If
the patient is found to be a carrier of the expanded repeat, the
embryos are biopsied and genetically tested for HD. Only embryos
without the HD mutation will be implanted. The patient will NOT be
informed how may eggs are harvested, how many eggs are successfully
fertilized, or how many embryos are implanted to protect them from
inadvertently determining their own genetic status. In vitro fertilization
can fail for many reasons,, and a failure to become pregnant should
NOT be attributed to carrying the HD gene.
Preimplantation genetic diagnosis can only be done for a single
genetic disorder due to the limited material obtained from the embryo.
All patients undergoing preimplantation genetic diagnosis will have
either a chorionic villus sampling or amniocentesis to confirm the
genetic test results from the preimplantation genetic diagnosis.
Patients have the option of having other genetic tests such as a
chromosome test to examine for Down Syndrome at the time of the chorionic
villus sampling or amniocentesis.
The cost of in vitro fertilization varies with each medical center
but may cost up to $17,000 for each cycle. Additionally, the cost
of the preimplantation genetic diagnosis is $2,000. Some insurance
companies will cover part or all of these costs. However, some couples
prefer to pay these costs out of pocket.
If you have questions, please call Jill Goldman, MS, CGC at (212) 305-7382.
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