HDSA Genetic Testing Guidelines

Huntington's Disease Society of America
Guidelines for Genetic Testing

• 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 into testing.
• 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 for testing.

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 America (HDSA).

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 Diagnosis

I. Presymptomatic Genetic Testing

This genetic test is for individuals at risk for HD who do not have symptoms.

II. Confirmatory Genetic Testing

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 uncertain.

To diagnose HD:

III. DNA banking

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 projects.

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 the family.

For more information on DNA banking and the Huntington's Disease Research Roster call (317) 274-5744 or email HDRoster@medgen.iupui.edu.

IV. Prenatal testing

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

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 period.

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 is done.

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.

V. Preimplantation Genetic Diagnosis (PGD)

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 use.

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 Jennifer Williamson-Catania, MS at (212)305-4655 or Wendy Chung, MD at (212)305-5040.

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