What is the genetic characteristic of Huntington's disease?

Huntington's disease is directly linked to a mutation on chromosome 4. This disease is caused by an expanded CAG repeat in the huntingtin gene (HTT) located on this chromosome. The abnormal number of CAG repeats leads to the production of a malfunctioning huntingtin protein, which subsequently affects nerve cells in specific areas of the brain, ultimately resulting in the characteristic symptoms of the disorder, such as movement disorders, cognitive decline, and psychiatric issues.

The identification of the specific chromosome is crucial for genetic testing and counseling, as individuals with a family history of Huntington's may undergo testing to determine if they carry the mutation. This knowledge is important for understanding the inheritance pattern, as the disease follows an autosomal dominant inheritance, meaning an affected individual has a 50% chance of passing the gene mutation to their offspring.

Therefore, the association of Huntington's disease with chromosome 4 is fundamental to both the pathology of the disease and its implications for affected families.