Hntington's Chorea

I am 29 years old. Since I was about 15 I have had these sometimes "uncontrollable" head twitches. I Also have very bad eye sight witch is getting progressivley worse. My Grandmother on my fathers side has died from Huntingtons Chorea and I just learned that my fathers sister is also suffering from the disease. My father is 53 and I don't believe he has shown any signs of the disease but he has not been tested. If my father does not carry the gene is there still a chance that I might?

[Jordanna Joaquina, MS, CGC]

Huntington's disease is caused by mutations in the HD gene on chromosome 4 at the location p16.3.

In the HD gene, there is a particular region that contains a DNA segment of three nucleotides (the building blocks of DNA) that are repeated multiple times. These repeats are called CAG trinucleotide repeats.

In most people, the number of CAG repeats in the HD gene ranges from 10 to 35. In this range, the HD gene produces a normal protein (appropriately called huntingtin). People with HD have an increased number of CAG repeats, which ranges from 36 to 120.
As the HD gene is passed from one generation to the next, the number of CAG repeats can expand, especially if inherited from the father's side. A larger repeat number is typically associated with an earlier onset of disease symptoms. This genetic phenomenon is called anticipation.

We all have two copies of the HD gene - one from each parent. In Huntington's disease having a mutation in a single gene copy is sufficient to cause the disease. This is called autosomal dominant inheritance.

An affected person has a 50% chance with each pregnancy to have an affected child. An unaffected person cannot pass on the condition.

We recommend that you, your father and your family meet with a neurologist for evaluation. You can also find medical centers and health professionals that specialize in Huntington's disease by going to the Huntington's Disease Society of America website and searching for "Centers of Excellence."