Huntington's Disease Causes & Risk Factors

Huntington’s disease is caused due to mutation in a gene called IT15 located on chromosome 4 (4p16.3) that is inherited as an autosomal dominant trait. This gene regulates, controls, or "encodes" production of a protein called Huntingtin and the pattern of inheritance is called autosomal dominant inheritance (4) & (5).

“HD is called an autosomal dominant disorder because only one copy of the defective gene, inherited from one parent, is necessary to produce the disease” (6).

Mutation of the gene IT15 causes abnormally long repeats of DNA instructions such as unusual, repeated sequences of the bases cytosine, adenine and guanine or CAG trinucleotide repeats leading to abnormal production of huntingtin protein. This defect adversely affects the production of certain brain enzymes, which are proteins involved in producing essential brain chemicals leading to damage and progressive loss of nerve cells in certain parts of the brain causing intellectual and mood problems.

People not suffering from HD tend to have about 20CAG repeats in the IT15 gene ranging from 9 to 29 whereas in those suffering from the disorder may have about 36 to 121 CAG repeats with a majority of the patients having more than 39 repeats. When the defective gene is inherited paternally, the CAG repeats are increasingly unstable leading to the development of symptoms at an early age relative to their fathers (4) & (5).

A child or an adult is at risk of inheriting or developing HD with 50% chance if one of his/her parent has the disease. In rare cases, one may develop the disease without a family history due to genetic mutation that could have happened during the father’s sperm development (7).

Conditions & Diseases: Brain & Nervous System

Huntington's Disease

Causes & Risk Factors