Huntington’s disease is a genetic disease, which means if you have it, you inherited it from one or both of your parents. It is caused by a hereditary fault on a specific gene.
A gene is a piece of hereditary information which is present in every cell of the body and tells cells what to do and when to do it. Genes are usually attached to a chromosome (a strand of DNA containing many different genes). Each human cell contains around 25,000 genes and most have 23 pairs of chromosomes.
The gene that causes Huntington’s is often called the huntingtin gene. It is attached to a chromosome number 4. It produces an important protein, called huntingtin, which is needed by nerve cells in the brain (neurons) and for the body’s development before birth.
When the huntingtin gene is faulty, the huntingtin protein it produces repeats certain genetic sequences too many times. This in turn appears to damage neurons in certain areas of the brain - although how and why this happens is not yet fully understood.