Prenatal & Preimplanation Testing in HD

Subject: FAQ Sheet -

Prenatal & Preimplanation Testing in HD

This information was a response to a question I asked Joyce Hammel July 24, 2000, the then HDSA - Medical & Scientific Manager:

In response to your question on pre-natal testing, I provide the following information:

There are several ways prospective parents can determine if their child will develop HD. The specific method of determining the embryo's genetic status depends on whether it was conceived naturally or through in vitro fertilization (IVF).

If the embryo was conceived naturally,

parents can use prenatal testing or non-disclosing prenatal testing to determine the child's genetic status.

During in vitro fertilization procedures, Preimplantation Genetic Diagnosis (PGD) can be used test embryos prior to their transfer to the uterus.

Prenatal Testing

The prenatal procedures currently available are amniocentesis and chorionic villus

sampling (CVS). Individuals or couples considering prenatal testing are advised to

seek genetic counseling prior to becoming pregnant. Prenatal testing is usually

requested in one of the two following circumstances:

1. In case I, a prospective parent has been diagnosed with HD or has been found

to be a gene-carrier and will eventually develop HD. In this instance, prenatal

testing can determine whether the child is

at 0 or 100% risk of developing HD.

2. In case II, the prospective parent is at 50% risk of developing HD and is pre-symptomatic. This means that one of his/her parents had HD but s/he isn't showing symptoms. Prenatal testing will reveal the embryo's and the parent's genetic status.

The test results in this case can be over-whelmingly traumatic if both are positive for HD. Prospective parents should be counseled about possible emotional ramifications before undergoing the tests.

Nondisclosing Prenatal Testing

If the parent who has a 50% risk for HD does not wish to know his/her gene status but the couple wants prenatal testing, then non-disclosing prenatal testing can be performed. In this situation, the embryo is at a 25% risk of developing HD.

Using linkage analysis, a procedure that compares the chromosomes of family members with that of the embryo, this test may reduce the fetus' risk from 25% to zero

or increase it to 50% Couples or individuals seeking this testing option are encouraged

to seek counseling and prepare for the test prior to conception.

Preimplantation Diagnosis

Preimplantation Genetic Diagnosis (PGD) can be used during in vitro fertilization (IVF)

procedures to test embryos for HD or other genetic disorders. This allows couples or individuals that have serious genetic disorders to decrease the risk of having a

child who is affected with the same problem.

At present, PGD is only offered in a few centers, usually under the supervision of an

institutional ethics review board, but its use may become more widespread in the near future.

There are only a few prenatal tests for HD done each year. The centers that do these

tests, especially the Genetics and In Vitro Fertilization Institute (GIVF) are experienced

with preimplantation diagnosis as well as CVS and amniocentesis testing for HD. GIVF

can also offer testing when knowledge of parental carrier status is not desired.

Please contact the following person at GIVF with additional questions about testing.

Lee Fallon, MS, CGC
Supervisor, Genetic Counseling
Genetics & IVF Institute
Fairfax, VA 22031
T: 703-698-3959
E-mail: lee_fallon@givf.com
Website: http://www.givf.com/

Hope that this information is helpful!

Joyce

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Other resources:

Physicians Guide Management of HD Second Edition indicates:

Prenatal testing for HD is possible, and should be performed in conjunction with detailed genetic counseling. Affected or at-risk individuals or couples should be informed of all of their reproductive options (shown in table 1), with the understanding that different options are appropriate or desirablefor different people.

For those who desire prenatal testing, the best time to make arrangements is prior to the pregnancy. Chorionic villus sampling can be performed very early, at 8-10 weeks, and a non-disclosing prenatal test, which determines only whether the fetus received a chromosome from the affected grandparent

or the unaffected grandparent, without determining whether the fetus or at-risk parent actually carries the HD gene, requires samples from several individuals.

TABLE 1: REPRODUCTIVE OPTIONS

Natural reproduction without genetic testing

Prenatal testing by amniocentesis or chorionic villus sampling

Non-disclosing prenatal test

Decision not to reproduce (may include sterilization)

Artificial insemination

Adoption

Surrogate mother

Pre-implantation genetic testing and embryo selection
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Pre-natal and Vitro

Fertilization for HD

Testing of a fetus (prenatal testing) presents

special challenges and risks; in fact some centers do not perform genetic testing

on fetuses. Because a positive test result using direct genetic testing means the at-risk parent is also a gene carrier, at-risk individuals who are considering a pregnancy are advised to seek genetic counseling prior to conception.

Pre-natal and Vitro Fertilization for HD continued

Some at-risk parents may wish to know the

risk to their fetus but not their own. In this situation, parents may opt for prenatal

testing using linked DNA markers rather than direct gene testing. In this case, testing does not look for the HD gene itself but instead indicates whether or not the fetus has inherited a chromosome 4 from the affected grandparent or from the unaffected grandparent on the side of the family with HD.

If the test shows that the fetus has inherited a chromosome 4 from the affected grandparent, the parents then learn that the fetus's risk is the same as the parent (50-50), but they learn nothing new about the parent's risk. If the test shows that the fetus has inherited a chromosome 4 from the unaffected grand-

parent, the risk to the fetus is very low (less than 1%) in most cases.

Another option open to parents is in vitro

fertilization with preimplantation screening.

In this procedure, embryos are screened

to determine which ones carry the HD

mutation. Embryos determined not to have

the HD gene mutation are then implanted

in the woman's uterus.

Source: NINDS Article

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New prenatal test offers quicker results Sept. 2001

LONDON, Sept. 27 (UPI) -- Scientists in England have developed a new prenatal

test that can more quickly determine whether a woman is carrying a baby with potentially life-threatening genetic abnormalities.

Researchers at Guy's and St. Thomas' Hospital National Health Service Trust in London report a test called quantitative fluorescence polymerase chain reaction significantly cuts down on the time patients and doctors wait for results. Although the extraction of amniotic fluid to study DNA, the genetic code for all cells, remains the same, advanced laboratory technology can produce answers to anxious parents in one or two days, compared to the current one week to two weeks it takes with standard testing.

The technique was tried for one year in which 1,148 amniotic fluid samples, 188 chorionic villus or fetal tissue samples and 37 other fetal tissue samples were examined.

Only 2 percent of the prenatal samples offered no information because the mother's cells contaminated the sample. But 98 percent did yield data on whether chromosomal abnormalities existed. Researchers in the United Kingdom could not be reached for comment. These results are reported in the Sept. 29 issue of The Lancet.

Separating the mother's cells from the fetus' can be painstaking. "It's like looking for a needle in a haystack," Dr. Paul G. McDonough, professor of obstetrics, gynecology, pediatrics and physiology at the Medical College of Georgia in Augusta, told United Press International. "And once you have those cells, you've got to be sure those are of the baby" leaving scientists with very small DNA with which to work.

It is crucial to examine the fetus' DNA because chromosomal abnormalities could indicate disease, such as Down syndrome, and if genetic tests are performed early enough in the pregnancy, results could affect whether a pregnancy is continued or not.

"Because the (standard) testing takes so long and because physicians and patients want results as soon as possible...there are a lot of investigators who are looking at ways for more rapid testing," Dr. Michael Mennuti, professor of obstetrics and gynecology at the University of Pennsylvania in Philadelphia and secretary of the American College of Obstetricians and Gynecologists, told UPI.

Mennuti cautioned, however, "if the rapid test doesn't look good, are you prepared to act on the basis of that?"

Mennuti said this kind of quick testing would make a useful screening tool for pregnant

women, but if there are problems, it should be followed up with standard prenatal tests before any decisions are made about the future of the pregnancy.

Still, Mennuti added, "We would be very interested in this...everybody has wanted

more rapid testing. This is a step in the right direction."

(Reported by Katrina Woznicki in Washington)

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There is excellent information on Preimplantation Genetic Diagnosis for

Huntington provided by Mark Hughes, MD, PhD on the MGH HD forum

for anyone interested: MGH HD Discussion

Dr. Hughes answered some questions with:

1) The oldest baby now, who was born through PGD to avoid genetic disease is

11 years old. The oldest one born to avoid HD is now almost 6 years old.

2) We work with clinics all over the nation. Yes - we still do this for free. I don't know for how much longer since the donations we have received are not keeping up with the demand. But we will hold out as long as possible.

3) I do not think I should post the actual names of clinics on a public web site. But we work with 4 large clinics in the NYC area as well as programs all up and down the coast (and across the country).

Our goal is to help desperate couples who seek to have a family, by providing them the opportunity to begin their pregnancy knowing that HD is not present in their baby.

Rather than post clinic info here, if you are interested in hearing more about all of this, you should call our genetics program at the Universtiy at 313-993-1353 and one of the genetic counselors will talk with you about your options in the NY area.

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Other Web Sites

The American Society for Reproductive Medicine page has lots of good links and consumer information. Atlanta Reproductive
Health Centres great Info

Genetic Diagnosis http://www.asrm.org/

This fact sheet covers how and why clinics do preimplantation diagnosis and lists the diseases that the procedure can screen out.

To look up any unfamiliar terms described above go to PersonalMD Medical Dictionary