Tools For Viewing
10 The Most Commonly Asked Questions
Clinical Trials & Research
Huntington's Disease~WeMove Info
Advocacy/Donations/Press Info
Clinical Definition & Search
Facing HD~Family Handbook
JHD Handbook-Chapter 1
JHD Info-Stanford Univ.
Physician's Guide To HD
Caring for People with HD
Physical & Occupational Therapy In HD
Understanding Behaviour in HD-Dr. Jane Paulsen
Understanding Behavioral-Dr. Edmond Chiu
Advanced Stages Caregivers Handbook
First Shift-Certified Nursing Assistants
Activities of Daily Living-HD
Unified HD Rating Scale (UHDRS) Motor Section
Westphal Variant
Age & Probability Chart
At Risk For HD-What Next?
At-Risk Checklist
Best Interest of Child?
Crystal Ball?
Food For Thought
Parent Hasn't Tested?
Q&A On Risk of Inheriting JHD
Testing Children
Genetic Disorders & Birth Defects
Genetic Testing for HD
Genetic Counseling-In General
Psychological Impact
Intro: Genetics/Genetic Testing
Prenatal & Preimplanation
Prenatal Testing-In General
o Genetic Testing Resources
o Personal Stories
Coping With The Early Years
Age of HD Appearance
Age of Onset-Historical
Family-HD Underestimated
Children of Parents With HD
Child~Parent Ill
Clinical Description JHD
HD - What Kids Are Saying
HD & Me
JHD-Duration of Illness
JHD-Clinical and Research
JHD Symptoms
Parenting With HD
Patients/Families Coping
Talking With Children About HD
5 Stages of HD
JHD Resources
Parent Resources
8 Fears of A Chronic Illness
Anxiety, Fears & Phobias
Apathy-Physician's Guide
Attention-Perceptual/Unawareness Physician's Guide
Bed/Pressure Sores
Bed/Pressure Ulcer Guideline
Behavior Management
Bi-Polar Disorders
Botulinum toxin therapy
Caring Tips
Child Abuse-Reconizing Signs
Chorea-Physician's Guide
Cognitive/Decision Making/Impulsivity
Cognitive-Short Tips
Contractures~Joints Locking
Dehydration-Physician's Guide
Denial of HD
Depression~Physician's Guide
Depression-Understanding It
Depression-How To Help
Depression - Treatment Resistant Patient
Depression-Other Resources
-Read If Your Child Is On Antidepressant
Disgust - Impaired Recognition in HD
Dissociative disorders
Driving - Physician's Guide
Dyslexia Resources
Dystonia/Rigidity & Spasticity Physician's Guide
Dystonia-Predominant Adult-Onset HD
Epileptic Seizures and Epilepsy
-Seizures ~Special Populations
Falling - Subdural Hematoma Risk
Fevers - Unexplained
Fevers, sweating & menstural cycles in HD
GERD (Stomach)
HD Principle Treatments
Hand muscle reflexes in HD
Hypothalamus - A Personal Theory
Insomia ~Physician's Guide
Irritability~Temper Outburst Physician's Guide
Learning Disability
Mania/OCD~Physician's Guide
Mood Disorder Rate In HD
Myoclonus (Movements)
Nails-What To Look For
Night Terrors
Obsessive Compulsive OCD
Panic Disorder
Personality disorders
Pneumonia-Advanced Stages
Pneumonia - Aspirated (Inhaled)
Prosody - Social Impairment
Sexuality~Physician's Guide
Skins Sensitivity
Sleep Disorders
Smoking-Physician's Guide
Why Certain Symptoms Occur
Symptom & Treatment Resources
Communication Resources
Communication Problems
Communication Strategies For HD~Jeff Searle
Hints For Weight Loss in HD
HD & Diet~HSA Fact Sheet 7
Nutrients: Some Possible Deficiency Symptoms
Nutrition and HD~Anna Gaba (Recipes)
Nutrition Information In HD~Naomi Lundeen
Speech & Swallowing~Lynn Rhodes
Swallowing & Nutrition Physician's Guide To HD
Swallowing & Nuitrition Resources
Swallowing Warning Signs
5 Swallowing Problems
Taste changes in HD
Weight Gain
-Feeding Tubes~Advanced Stages of HD
-Feeding Tube~Jean Miller
-Feeding Tubes: One More Word ~Jean Miller
-Feeding Tubes & Baby Foods
-Feeding Tube~Dental Care
-Feeding Tube Instructions~Jean Miller
-Feeding Tube Resources
Finding a Therapist - Behavoir
What Is A Physiotherapist?
Physical Therapy In HD
Speech-Language Therapy
Therapy Descriptions
Therapy Resources- Easter Seal
Therapy Resources
HD Treatments
Medications-Movement Disorders
Medication/Emergency Info Forms
Cutting Prescriptions
Drugs-Look 'Em Up
-Adolescents Under 25
-Antidepressant Adverse Effects
A-Z Mental Health Drugs
-EPA~Fish Oil
-Haldol/Haloperidol - Clinical Sheet
-Haldol~Clinician Description
-Haldol & HD
-Haldol/HD Patient Experiences
-Haldol~ Patient Handout
-Mood Stabilizers: ASK 3 Questions
-Neuroleptic Malignant Synd WARNING
-Olanzipine-Risperidone/blood tests
-Psychiatric Drugs & Children
Sertraline ~Zoloft
-Spasticity Meds/Treatments
-SSRI Medications
-Tardive Dyskinesia WARNING
-Weight Gain Medications
-Sites/Help the Medicine Go Down
-Vitamin & Mineral Deficiencies
Surgery-Movement Disorders
o Surgery Resources
Clinic Visits-How To Prepare
CT Scans, MRI's etc.
Swallowing Tests
Tests Commonly Used
o Procedures Resources
Alcohol-Parent's Guide
Alcohol-Talking To Your Child
Drugs-What To Do?
Drugs-Talking To Your Child
Disciplining-Ages 0-13 & Up
Straight Talk On Suicide
Teen Suicide-You Need To Know
o Suicide Resources
Divorce & Child Stress
Tips For Divorcing Parents
Guides To Disability Issues
Caring-Child & Medical Technology
Caring for a Seriously Ill Child
Child Long Term Illness
Disability-Special Education Plan
IFSP Early Intervention Process
Disability Resources
Financial Planning
Wishes Can Come True-Children's Wish Foundations
Special Needs Resources
Special Needs Camp - About
Special Needs Camp - Finding One
Child Assistive Technology
Adaptive Equipment Resources
Signs of Unhealthy Self-Esteem
Emotional Behavior Links
o Emotional Support Resources
Helping Child Deal With Death
o Grief Addtional Resources
ADD & Teens
Conduct Disorders
FAQS & Related Info
Understanding AD/HD
What Is AD/HD?
Research Articles
HD Support Groups
National Youth Association
HD Links
Related Resources
Tips For Friends
HD Disability
Benefits Check UP - See What You Can Get
Medical Insurance Bureau's Facts On You!
Medicare Rights-Home Health & Hospice
Medicare Rights Center Resources
No Insurance? Try This!
Prescription Drug Cards Part I
Prescription Drug Cards Part II
Social Security-Children With Disabilities
Caregiver Self-Assessment
Caregiver's Handbook
"First Shift With A Person With HD"
Getting Respite Care/Help At Home
Helpful Forms-Info
Home Emergency Preparations
Symptom Management
Ten Tips
Useful Tools
Our Personal Experience
Coping At The End
Kelly E. Miller
Song & Verse
Letter From My Heart
Genetic Testing for HD


Genetic Testing for Huntington's Disease

Source:  HDSA http://www.hdsa.org/edu/genetictesting.html


Statements and opinions in this guide are not necessarily those of the
Huntington's Disease Society of America, nor does HDSA promote,
endorse, or recommend any treatment or therapy mentioned herein. 
The reader should consult a physician or other appropriate health care
professional concerning any advice, treatment or therapy set forth in
this book



What is Huntington's Disease (HD)?
  1. How do I know if I am at risk for HD?
  2. Can I get HD in any other way?
  3. If I was born with the gene, then why don't I have HD now?
  4. Has the gene for HD been identified?
  5. How does this gene work?
  6. If all people have the gene for HD, why do only some develop the disease? 


  1. How can I be tested?
  2. What does presymptomatic testing entail?
  3. Should I bring a friend with me?
  4. Are blood samples from my family members necessary for testing?
  5. How much does it cost?
  6. Will health insurance pay for testing?
  7. Are the results of the tests always accurate?
  8. Are the test results confidential?
  9. If the test results cannot tell me when the disease will begin,
    how will I know if I am beginning to show symptoms?
  10. Should I be tested for HD?
  11. Where can I find help in making this decision?
  12. Is there a "right" time to be tested?
  13. Should children be tested?
  14. Is prenatal testing available?
  15. What is confirmatory testing?

 Huntington's Disease and the HD Gene

What is Huntington's Disease?

Huntington's Disease (HD) is a hereditary degenerative brain disorder
which leads to both physical and mental disabilities.  Symptoms usually
appear between the ages of 30 and 50, but the disease may strike
those as young as two or as old as 80.  Initial symptoms may include
difficulty in concentration, depression or twitching, but each person
who has HD is affected differently and early symptoms vary from
person to person.

Testing is available to determine whether a person has the gene for HD. 
The decision about whether or not to be tested for HD is one which
requires careful consideration.  This booklet will answer the most common
questions regarding testing.  

How do I know if I am at risk for Huntington's Disease?

Huntington's Disease is inherited in an autosomal dominant pattern. 
This means that every child born to a person who has HD, regardless of
gender, has a 50 percent, or one-in-two, chance of inheriting the gene
that causes HD.  Men and women are equally affected, so that either
parent may pass on the HD gene to any offspring.
Does that mean that exactly 50 percent of the children of a
person with HD will develop the disease and 50 percent will not?
No, each child has the same 50 percent risk of having inherited the gene
for HD regardless of whether or not any brothers and sisters have it.
Can I get HD in any other way?
No, you cannot "catch" HD from another person.  You must be born with
the gene for HD in order to one day develop this disorder.
In some cases, a person may develop what appears to be HD even
though there is no known family history of the disorder.  There are
many reasons why this may be.  Perhaps the parent who had the
gene for HD died at an early age, before the symptoms appeared, or
maybe other family members had HD but were misdiagnosed as
having Parkinson's disease or another disorder with HD-like characteristics. 
In cases like these, doctors may recommend genetic testing to confirm
or rule out a diagnosis of HD.
If I was born with the gene, then why don't I have HD now?
We inherit our genes from our parents and therefore we are born with
them.  Some genes are "turned on" only at later stages of our lives. 
A good example is the gene for baldness.  Many people are born with
this gene but it is only in adulthood that it is activated and that people
begin to lose their hair.  Also, people who have the same gene for
baldness may begin losing their hair at different ages.
Has the gene for HD been identified?
Yes, the gene for HD was found in 1993.
How does this gene work?
Each person has 23 pairs of chromosomes in all of the cells of his/her body. 
Genes lie on these chromosomes and are made up of deoxyribonucleic acid,
or DNA.  It is estimated that humans have about 100,000 genes which
influence development, growth and functioning of the body, and are passed
down from parents to children.
The gene for HD lies on the short arm of chromosome four.  It is actually a
segment of DNA which contains a strip of repeated "trinucleotides" at one
end.  Nucleotides are the building blocks of DNA.  The trinucleotide repeat
involved in HD is cytosine-adenine-guanine, or CAG.
Everyone has two copies of the gene for HD.
If all people have the gene for HD, why do only some develop the disease?
Whether a person will or will not develop Huntington's Disease can be
determined by the number of CAG (or trinucleotide) repeats contained within
their copies of the HD genes.  People who have inherited the gene which
causes HD have a higher number of repeats, usually above 40.  No one with
35 or fewer CAG repeats has been known to develop HD symptoms. 
Individuals who have an HD gene with 36-39 repeats may or may not
develop the symptoms of HD within a normal life-span.
The number of CAG repeats may change as the gene passes from parent
to child - so that the child may have slightly more or fewer repeats than the
parent.  The tendency for an increased number of repeats is more common
when the gene is passed from father to child than when a mother transmits
the HD gene.
HD is inherited in a dominant fashion.  This means that a person need have
only one copy if the gene with a high number of repeats in order to develop
the disease.
It is important to note that the number of repeats is significant only in
determining whether a person will or will not develop HD.  The number of
repeats is not known to be correlated with the course of the disease, and
a particular repeat number does not predict a specific age of onset.  The
exception to this is that a very high number of repeats is indicative of the
juvenile form of HD with age of onset prior to age 20.
How can I be tested?
A blood test is now available that can determine, in almost all cases,
whether a person has the HD gene.  This test cannot, however, predict
when symptoms will begin or the course of the disease.
There are three categories of testing:
  1. Presymptomatic testing, for people at risk for HD, is the type of
    testing which will be discussed in greatest detail in this booklet.
  2. Confirmatory testing determines whether people showing
    possible HD symptoms actually have the HD gene.
  3. Prenatal testing is used to determine whether a fetus has the
    HD gene. This can be done by amniocentesis or chorionic
    villus sampling (CVS)
What does presymptomatic testing entail?
The Huntington's Disease Society of America recommends that at-risk persons
who wish to undergo presymptomatic testing do so at an HD testing center.
The testing centers involve teams of professionals who are knowledgeable
about HD.  A list of these testing centers is available from HDSA.
The testing procedure involves sessions with various professionals.  It typically
includes one session devoted to each of the following: genetic counseling; a
neurological exam; a psychological interview; discussion of the results; and
follow-up. The genetic test itself is a blood test.
The purpose of these sessions is to ensure that the person about to undergo
testing understands the implications of this knowledge and is prepared to
receive the results. The neurologic exam will determine if any early symptoms
of HD are present.  If the person is found to be symptomatic, he/she will be
offered the option of discontinuing the test procedure.
The person may withdraw from the testing process at any time.
The sessions of the testing process are usually spread out over one month or
more and require repeat visits to a testing center.  Exceptions are sometimes
made if a person lives far away from the center or in other circumstances. 
Decisions concerning scheduling of appointments can only be made by those
who will perform the testing.
Should I bring a friend with me?
It is strongly encouraged that you bring a support person/partner with you
to all testing sessions.  The partner should be a spouse, companion or a close
friend.  It is not advisable to bring a sibling or another person who is at risk for HD.
The partner will be able to provide moral support during appointments, when
awaiting test results, upon receiving the results, and thereafter.
Are blood samples from my family members necessary for testing?
No, you do not need to obtain blood samples from others in your family.  However,
the testing centers do encourage you to have available either a blood sample from
a family member who has HD or the results of his or her genetic test.  This is to
ensure that the illness in the family is indeed HD.  Some people are misdiagnosed
as having HD when, in fact, they have another neurological disorder.  Therefore it
is important to establish that the affected family member has HD.  This type of
testing is usually reimbursable by insurance.
How much does it cost?
The cost of testing varies from center to center.  Some centers are research facilities
and will  perform the test free of charge for those involved in their studies, some
have sliding fee scales, and others charge anywhere from $600 to $1,500.
Will health insurance pay for testing?
You need to check with your insurance provider to see if they cover presymptomatic
testing.  However, before doing so, you should weigh the risks and benefits of
submitting a claim.  Unfortunately, genetic discrimination does exist.  Though
unusual, it is possible for an insurance company to deny health coverage or to
cancel an existing policy should a person be found to carry the HD gene.  A positive
test result may also be considered a "pre-existing condition" which could make it
difficult to obtain future health insurance coverage.  In a number of states, laws
do exist which prohibit genetic discrimination by insurers, and a similar federal
law is being considered.
Many people choose to wait until they have the results of their genetic test before
seeking reimbursement from their insurance company.  They then do so only if
they do not have the gene.
Are the results of the test always accurate?
The accuracy of positive or negative results is almost 100 percent provided that
another family member is known to have the gene for HD.  Test results cannot
determine if a person will develop HD if the number of CAG repeats falls into the
intermediate range.  Also, positive test results cannot predict when the symptoms
of HD will begin.
Are the test results confidential?
Test results should be kept confidential and should only be given to another person
with your written permission.  On an initial call to a testing center, you should ask
how confidentiality is ensured.
If the test results cannot tell me when the disease will begin, how will I know if
I am beginning to show symptoms?
HD can only be diagnosed by a neurologist.  A neurological exam can determine
if you have symptoms of HD.
Should I be tested for HD?
The decision to undergo genetic testing is an intensely personal one that cannot
be taken lightly.  Testing should never be mandated or forced upon an at-risk
individual.  There are no "right" or "wrong" answers.  Of course, everyone will
have his/her own circumstances to take into consideration.  The following are
some of the issues to think about and/or discuss with those who are closest
to you:
Will your relationship with your spouse or significant other change once your test
result is known?  Does he/she want you to take the test?  How will a positive or
negative result impact your future together?  
Relationships with siblings are sometimes strained by learning a test result. 
There is often guilt felt by siblings who do not carry the gene (although they had
no control over which gene they inherited).  Those who have the gene may
express anger toward brothers and sisters who do not.
Children often factor heavily in the testing decision.  Many people undergo
presymptomatic testing before planning a family.  Others use the result to decide
if they will have more children.  Those who already have children worry about
the impact of a positive test result.  They may ask themselves questions such
as: How will I tell the children that they may have inherited the gene from me? 
How will I explain to them that I will one day show the symptoms of HD?  How
will this affect their lives?
Parents may feel guilty for having had children knowing that HD was in their
family (even if they were not aware of their own risk for inheriting the gene at
the time they had children).
Your relationship with your parents may also be affected by the test result. 
Parents may feel guilty for passing on the gene.  An unaffected parent may
be upset by the thought of having to watch his/her child live with HD.   A
parent may also have mixed emotions in the event that one child tests
negative for the HD gene while another tests positive or begins to show
Friends are among those to whom we turn for support.  You may choose to tell
a close friend (or friends) about your decision to be tested for HD.  Should you
choose to be tested, make certain that you share your decision only with people
you trust will not discuss it with others.
Most people will have a strong emotional response (either immediate or sometime
in the future) when they are told whether they do or do not carry the gene. 
However, most people adjust well to the results after some time has passed.
Where can I find help in making this decision?
There are different resources available to aid you in making your decision.
The HD testing centers are staffed by professionals with the knowledge and
expertise to help you decide whether or not to take the test.  If you want long
-term counseling, an HDSA chapter social worker or the staff at the HD
testing center may be able to provide you with a referral to a knowledgeable
You may also consider joining a support group.  There are HD support groups
in virtually every state and some groups are specifically for those who are at
risk.  Your local HDSA chapter or the HDSA national office can help you locate
a support group in your area.
It is often helpful to read how others arrived at their decisions.  Two publications
which discuss this are Experiences of Predictive Testing for HD (a collection of
personal accounts - available from HDSA as part of the Testing Packet) and
Mapping Fate: A memoir of Family, Risk, and Genetic Research by Alice Wexler
(published in 1995 by Random House).
Another helpful resource is Walking the Tightrope: Living at Risk for Huntington's
Disease by Randi Jones, Ph.D.  This book provides professional insights and
practical guidance for people at risk for HD.
Is there a "right" time to be tested?
Although all of us face stresses in our daily lives, one should not undergo testing
at the time of a particularly stressful event (a death in the family, divorce,
diagnosis of HD in a loved one, or some other traumatic experience).
Should children be tested?
Testing of children (those under 18 years of age) is strongly discouraged. 
If a child is exhibiting symptoms of HD, a neurologist who is familiar with
HD should be consulted.  Genetic testing may then be recommended as
a confirmatory measure in some cases.
Given that each person should decide for him- or herself whether or not
to be tested, minors should wait until they can arrive at this decision for
themselves.  Testing of children may also expose them to discrimination
by health insurance companies, employers, and perhaps (consciously or
unconsciously) by their parents.
Is prenatal testing available?
It is possible to determine if a fetus is carrying the gene for HD.  The prenatal
procedures currently available are amniocentesis and chorionic villus sampling
(CVS).  It is advisable for a couple to discuss prenatal testing options with a
genetic counselor prior to becoming pregnant.  If an at-risk partner wishes to
be tested for the HD gene, it is recommended that the testing process be
completed before conception.
If the parent who has a 50 percent risk for HD does not wish to undergo
testing but the couple wants prenatal testing, then nondisclosing tests can
be performed.  Nondisclosing testing is performed by linkage analysis.  Linkage
analysis compares the chromosomes obtained from the blood samples of
several family members to those of the fetus.  In this way, the risk that the
fetus is carrying the gene for HD can be estimated.  A genetic counselor should
be consulted well before conception since blood samples from family members
must be obtained and analyzed in this type of testing.
What is confirmatory testing?
Confirmatory testing is used to "confirm" a neurologist's suspicion that a
person has HD.  It is a type of genetic testing which is often performed by a
neurologist when a patient has symptoms which appear to be those
generally associated with HD.
It is important to bear in mind that, even though a person may be aware
that he or she has some of the symptoms associated with HD, hearing this
suspicion confirmed can often have a significant psychological effect.
How can I find out where testing centers are located?
The HDSA publishes a list of testing centers which is available free of charge.
Is any research being done to find treatments or a cure for HD?
The key to better treatments and an eventual cure is research.  There have
been many exciting breakthroughs in recent years, including finding the gene
that causes HD in 1993.  In 1995 huntingtin-associated protein (HAP 1), a
protein which works along with huntingtin (the protein which is expressed
by the HD gene), was discovered.  Research is underway to determine how
these proteins, and possibly others, are tied to the symptoms of HD.
An international coalition of scientists, known as the Huntington Study Group
(HSG), was formed in 1993 to conduct clinical and basic scientific research in
a coordinated, systematic fashion.  HSG sites combine research facilities with
teams of professionals who have expertise in treating HD.  The Group has
begun to test new drugs which could potentially lead to effective treatments
for HD.
In 1997, the Huntington's Disease Society of America established the HDSA
Coalition for the Cure, a consortium of 14 top laboratories in North America
and Europe. Coalition investigators focus on four key areas of study: animal
models, cell models, biochemistry and cell biology.  Through HDSA funding,
semi-annual meetings and the sharing of data and ideas, the Coalition is
accelerating the pace of HD research.
While there is currently no cure for HD, treatments are available which can lessen
the severity of some of the symptoms.  A neurologist or psychiatrist who is
knowledgeable about HD can prescribe appropriate medications, and physical,
occupational and speech therapists should also be consulted in the early stages
of HD to be optimally effective.
Where can I go for more information?
Additional publications bout Huntington's Disease, genetic testing, and related
issues may be obtained from
Huntington's Disease Society of America
158 West 29th Street,  7th Floor
New York, NY 10001-5300
1-(800) 345-HDSA or (212) 242 1968.