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Causes of Huntington's disease

Huntington’s is caused by an error in the genetic code that programmes the way the body works. The mistake lies in a defective gene on chromosome 4. This gene produces a protein called Huntingtin. The pattern of inheritance in Huntington’s is called autosomal dominant inheritance.

The defect affects the production of certain brain enzymes, which are proteins involved in making essential brain chemicals. This leads to damage and progressive loss of the nerve cells in certain areas of the brain (causing intellectual and mood problems) and a build-up of the brain chemical dopamine (causing the movement problems).

The parent with the Huntington’s gene have one good copy of the gene and one faulty copy of the gene, so there is 50:50 chance the child will get the faulty gene. With each pregnancy involving the gene-carrier as a parent, there is a 50:50 chance that the defective gene will be passed on. If Huntington’s is inherited from the father it tends to be more severe.

In as many as 3% of cases there is no family history of the disease. This could be due to adoption or because relatives with the disease died early from other causes, or it could be a new genetic mutation (a new error in a gene).

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