CAG repeats-Testing Children


What Is Huntington's?
Facing HD~Family Handbook
SECTION 1 - At Risk
At Risk For HD-What Next?
Testing Children
~~Chapter 1 JHD Handbook
Best Interest of Child?
Crystal Ball?
Parent Hasn't Tested?
Food For Thought
Age & Probability Chart
CAG repeats-Testing Children
SECTION 2 - Genetic Testing
At-Risk Checklist
Genetic Testing for HD
Genetic Counseling-In General
Psychological Impact
Intro: Genetics/Genetic Testing
Prenatal & Preimplanation
Prenatal Testing-In General
Related Resources
Children of Parents With HD
Child~Parent Ill
Clinical Description
Family Dynamic Alterations in HD
What Kids Are Saying-HD
~~HD & Me
JHD-Duration of Illness
JHD-Clinical and Research
JHD Symptoms
Parenting With HD
Patients/Families Coping
Talking With Children About HD
Resources on JHD
SECTION 4 - Symptoms
Activities of Daily Living
8 Fears of A Chronic Illness
Anxiety, Fears & Phobias
Behavior Management
Caring Tips
Child Abuse-Reconizing Signs
Chorea-Physician's Guide
Communication Problems
Dehydration-Physician's Guide
Denial of HD
Depression~Physician's Guide
Depression-Understanding It
Depression-How To Help
Dystonia/Rigidity~Physician's Guide
Epileptic Seizures and Epilepsy
GERD (Stomach)
HD Principle Treatments
Insomia ~Physician's Guide
Mania/OCD~Physician's Guide
Myoclonus (Movements)
Nails-What To Look For
Night Terrors
Obsessive Compulsive OCD
Sexuality~Physician's Guide
Skins Sensitivity
Sleep Disorders
Speech & Swallowing
Swallowing & Nuitrition
5 Swallowing Problems
Swallowing Warning Signs
Why Certain Symptoms Occur
SECTION 5 - Therapies
Finding a Therapist - Behavoir
Speech-Language Therapy
Related Resources
SECTION 6 - Medications
Medications-Movement Disorders
Adolescents Under 25
Antidepressant Adverse Effects
Anti-psychotic Medications
Psychiatric ~ Children
SSRI Medications
Drug Resources
SECTION 7 - Surgery
Surgery-Movement Disorders
Related Resource
SECTION 8 - Procedures
CT Scans, MRI's etc.
Swallowing Tests
Tests Commonly Used
Related Resources
SECTION 9 - Alcohol/Drugs
Alcohol-Parent's Guide
Alcohol-Talking To Your Child
Drugs-What To Do?
Drugs-Talking To Your Child
Disciplining-Ages 0-13 & Up
SECTION 10 - Suicide
Straight Talk On Suicide
Teen Suicide-You Need To Know
SECTION 11 - Divorce
Divorce & Child Stress
Tips For Divorcing Parents
SECTION 12 - Disabilities
Caring-Child & Medical Technology
Caring for a Seriously Ill Child
Child Long Term Illness
Disability-Special Education Plan
Financial Planning
Finding A Special Needs Camp
Special Needs Camp
SECTION 13 - Assisstive Help
Child Assistive Technology
SECTION 14 - Emotional
Signs of Unhealthy Self-Esteem
Emotional Behavior Links
Related Resources
SECTION 15 - Grief
Helping Child Deal With Death
ADD/ADHD Research Articles
ADD & Teens
Conduct Disorders
Understanding AD/HD
What Is AD/HD?
SECTION 17 - Support
HD Support Groups
National Youth Association
SECTION 18 - Links
HD Links
Helpful Forms-Info
Related Resources
Tips For Friends
SECTION 19 - Benefits
HD Disability
Section 20 - My Experiences
Our Personal Experience
Coping At The End
Kelly E. Miller
Song & Verse
Letter From My Heart


From the 6/01 Juvenile HD Handbook states: (all taken directly from this book)

For reasons that only became clear after the gene responsible for HD was
discovered in 1993, individuals with a very early onset of HD are far less
likely to have an affected father than an affected mother.  It is very
unlikely for HD to appear in a child whose parent was not also affected
with HD.  If this situation appears to be present, the physician should consider
diagnosis other than HD.
Occasionally an HD-affected child without an affected parent can be
explained by the early death of a parent (before the parent's symptoms
were evident), misdiagnosis or lack of diagnosis in a parent who was
affected, non-paternity (a biological father who is not the same as the
apparent father), onset of symptoms in the child before the parent's onset,
or adoption.
Documenting the diagnosis of HD in other relatives can be helpful to the
physician as the child is evaluated for HD.   A parent who suspects that his
or her child has juvenile HD can help the physician by assembling information
about the family history.
If the family history is missing because the child was adopted, it may still be
possible to obtain the missing information if it is important to the child's
diagnosis.  Adoption agencies and county or regional social services departments,
when given an understanding of the serious nature of HD and its hereditary
pattern, may be able to contact the birth parents to obtain more information.
Similarly, a mother or family who becomes aware of the family history of HD
should be honest and open with the adoption agency, so the adopting parents are
aware of the child's genetic risks and are able to plan appropriately.
The ability to detect changes in the HD gene itself has made confirmation of the
diagnosis of HD much simpler.  The HD gene can be isolated from a blood sample,
and examined chemically; the abnormality in the gene that causes HD is called a
"CAG repeat expansion."   The HD gene normally has a variable number of
"CAG repeats" - any number up to 35 repeats is normal.
There is a relationship between the repeat numbers and the age that HD
symptoms begin, so that higher repeat numbers are associated with
younger ages of onset.
Most adults with HD have between 40-50 CAG repeats in their abnormal
HD gene.  Usually, juvenile HD is associated with CAG repeat numbers
of 50 or higher, although it is not possible to define rigid boundaries.
Very young age of onset are associated with very high CAG repeat numbers;
children with HD onset  at age 2-3 years and with over 100 CAG repeats
have been reported.
The gene test is close to 100% accurate.  If the tests show two normal
HD genes, the child will never develop HD and is not at-risk for passing
HD on to his children.
If the test shows an abnormal HD gene, the child will someday develop HD.
The gene test, however, cannot predict when a particular person's
symptoms will begin.
Occasionally, individuals will have a CAG repeat length in the 36-39
range, which may or may not be associated with the development of HD
symptoms during a normal life span.   Results in this "intermediate range"
are not usually a factor when testing children for possible symptomatic HD.
And rarely, very high CAG repeat numbers (over 100 CAG repeats) are
not detected by the standard gene test.  If HD is strongly suspected in a
very young child who has a normal gene test results, the physician may
want to contact the laboratory or a genetic counselor to discuss the
possibility of a special analysis to look for very large CAG repeat numbers.
The potential risks of testing a child for the HD gene inappropriately or
prematurely cannot be emphasized enough.   Individuals who develop HD
have the CAG repeat expansion in one of their HD genes from the moment
of conception - years or decades before their symptoms begin.
There are two ways in which a premature gene test can be misleading or
damaging to a child's care. 
First, an abnormal gene test result may incorrectly be assumed to "explain" a
child's symptoms, when in fact the symptoms are not clearly related to HD.  
For example, an adult whose gene test was felt to "explain" his blurry vision
and headaches was incorrectly diagnosed as having HD and, as a result, the
diagnosis of his pituitary tumor was delayed.
Secondly, it is possible that a gene test will show a small CAG repeat
expansion, one that is likely to be associated with adult-onset HD but not
juvenile onset HD.   This is equivalent to a predictive gene test and does
not help to explain the child's current symptoms.
Due to the very sensitive nature of the gene test results, it is important for
counseling to occur before the results are given, so there are no misunderstandings
about their significance.  If the physician is unable or does not have the time
to explain the gene test in details, a genetic counselor may be asked to help
with this part of the process.
When one child has been diagnosed with HD, parents may want to have their
other children tested as well.   Testing of a person who does not have symptoms
of HD is called predictive testing, in order to distinguish it from diagnostic
testing for a person who has symptoms suggestive of HD.
Although, at first thought, it may seem reassuring for parents to find out
that their other children do not carry the HD gene, it is very important to
consider the complex potential effects of the tests results on the entire
family, as well as on the individual or individuals being tested.
The risks of premature genetic diagnosis of HD have already been discussed
and genetic testing experts believe that predictive tests should be reserved
for individuals who are able to understand the potential risks and benefits
of the test and who are able to give informed consent. 
Experience in the United States has shown that most adults at-risk for HD
do not choose to undergo predictive genetic testing, so a parent who requests
predictive testing for a child is most likely doing something that the child
would not want if he or she were able to make the choice.
In addition, at this time, there is no medical advantage to knowing that
someone carries the HD gene - treatments that prevent or delay the
disease have not been developed yet.
For all these reasons, most genetic professionals in North American
decline parental requests for predictive tests on their asymptomatic
children.  Occasional exceptions might be made for adolescents in
adult situations, such as an "emancipated minor" or a married teenager.
In the United States, potential adoption is not usually felt to be an
appropriate indication for HD predictive testing, because of the potential
for social, financial, educational, insurance and employment discrimination
based on the test results and the lack of medical treatment or care to
balance the potential social harms.  Other countries may have different