CAG repeats and Genetic Testing in Children
Movement Disorder Medicines
Anxiety-Antidepressant Medications
Antidepressant Adverse Effects
Warnings~Adolescents Under 25
Sertraline ~Zoloft
Anti-psychotic Medications
Prozac, Luvox, Paxil, Zoloft & Celexa
Olanzipine & Risperidone and blood tests
Cutting Prescriptions
Sites That Help the Medicine Go Down
Vitamins & Minerals
Why Certain Symptoms Occur In HD
Tests Commonly Used -Neuropsychological Examination
Symptom vs Medication
Speech & Swallowing Difficulties~Lynn Rhodes
Swallowing Problem Warning Signs
Swallowing Tests
Nutrition and HD~Anna Gaba (Recipes)
HD & Diet~HSA Fact Sheet 7
HD~Swallowing & Nutrition
Weight Gain
5 Levels Difficulty In Swallowing
Feeding Tube~Advanced Stages of HD
Feeding Tube~Jean Miller
One more word on feeding tubes
PEG Tubes and baby foods
Feeding Tubes-More Info
HD~Falling/Safety Issues
HD~Cognitive/Decision Making/Impulsivity
Cognitive-Short Tips
Denial of HD
HD~Irritability/Temper Outbursts
Managing behavioral problems
Depression - Treatment Resistant Patient
HD~Mania, Obsessive Disorders
HD~Hallucinations & Psychosis
HD~Rigidity, Spasticity, and Dystonia
Adaptive Products
Teen Suicide~Let's Talk Facts
Stress Explained-Easy/Fun Format
How To Help Someone Chronically Ill
Legal Planning for Incapacity
Out-of-Home Care Options FAQ
Preparing for Emergencies
CAG  Repeats and Genetic Testing in Children
2001 Junvenile Huntington's Disease Handbook
"A Guide For Physicians, Neurologists and Other Professionals"
Written and Edited by Martha Nance, M.D.
This guide may be purchased through the HDSA 1-800-345-4372
For reasons that only became clear after the gene responsible for HD was discovered in 1993,  individuals affected with a very early onset of HD are far more 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 infor-mation 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 , 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 re-assuring 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 pro-fessionals 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 practices.