Genetic Testing & Terminology

Huntingtons Disease Genetic Testing


Scientists identified the gene responsible for HD in 1993. This made it possible for those people at risk of the disease to undergo genetic testing to find out if they have inherited the gene. Candidates for testing must be eighteen years of age or older, and must want to know their gene status. Extensive support, information and counselling are available.

There is no requirement or expectation that those at risk of HD must be tested. In fact, roughly 85% of people at risk choose never to be tested. It is an entirely personal decision, and you should take time to speak with your doctor of Genetic Health Queensland (GHQ) before you make a decision.

If you choose to undergo genetic testing, you will undertake a series of genetic counselling sessions. These sessions ensure you are prepared for both the testing process and the implications of the results, whatever they may be. This process, from initial consultation to receiving your results, can take many months.

The test results will either be negative or positive. A negative test result means you do not carry the faulty HD gene. A positive test result means you do carry the faulty HD gene.

Due to the genetic nature of HD, your test results may impact others in your family who are at risk. If you have a positive test result, it means that your parent also has the faulty gene, and your siblings may as well. If you receive a negative test result, this does not change your parent or siblings’ at-risk status.

Genetic Health Queensland (GHQ) coordinates the predictive testing program in Queensland, and is funded through the public healthcare system. Individuals can be referred to the service by their local doctor or specialist by writing to:


Genetic Health Queensland
Royal Brisbane Women’s Hospital
Herston Road, Herston, Q. 4029
Telephone: (07) 3646 1686
Fax: (07)3636 1987


When you speak with GHQ, they will discuss your family history to determine that you are or may be at risk, and will advise you further about the testing process.

CAG Repeats

Every person in the world lives with the Huntingtin protein, which contains a small section of repeated DNA. This is known as the CAG repeat. In those people who develop HD, the CAG repeat occurs too many times.

When testing for HD, the scientist or health professional will look at the number of CAG repeats in the person’s Huntingtin protein. The number of repeats will determine the likelihood of a person developing HD.

HDBuzz-sourced image explaining penetrance

This image was sourced from HDBuzz, where you can read more about CAG repeats and penetrance.


“At risk”

Being at risk for HD means that one of your direct biological parents carries, or is at risk of carrying, the faulty gene that causes HD. You are considered at risk unless your parent receives a negative test result, or you have tested (negatively or positively) for the gene. In Australia, children under the age of 18 cannot be tested for the faulty gene, so all naturally-conceived children with an at-risk or HD-positive parent are at risk.

If your at-risk parent takes a genetic test and is found not to carry the faulty gene, then you will no longer be at risk. If your at-risk parent is found to carry the faulty gene, you will still be considered at risk.

“Gene Negative”

“Gene negative” means you have been tested for HD and your test result was negative. You do not carry the faulty gene, you will never develop HD, and you cannot pass it on to any of your children. Your parent may still carry the faulty gene and is still considered ‘at risk’ (if they have not been tested), as are any siblings who remain untested.

“Gene positive”

Gene positive means that you have taken the genetic test, and you carry the mutated gene. If you carry the gene, you will develop HD at some point in your life, and your children are at risk of inheriting the disease from you. People are considered gene positive if they have the faulty gene but do not yet have any symptoms of HD.


Symptomatic means you are displaying symptoms of HD, following a positive test result or diagnosis from your doctor.