What are the causes of Huntington’s disease?

Chorea Huntington is a genetic disease. It’s caused by a genetic defect. The protein that causes the disease is called huntingtin.

The gene coding for it is located on the short arm of chromosome 4. The mutation of the huntingtin protein causes the death of special nerve cells in certain regions of the brain. This is a slowly progressing process, which is why the disease is also classified as a so-called neurodegenerative disease.

Many pathological processes in connection with the disease have not yet been fully researched. However, it is known that Huntington’s disease is a trinucleotide disease. In healthy people, a certain triple combination in the DNA is repeated up to 20 times.

In patients with Huntington’s disease, this combination repeats much more often, between 60 and 250 times. As a result, the gene can no longer be read correctly and the Huntingtin protein is assembled incorrectly. The more often this repetition occurs, the earlier symptoms appear in the affected patients. The more repetitions that can be detected in a patient, the more severe the course of the disease.

Diagnostics:

Collection of the patient’s medical history and question about the occurrence of Huntington’s disease in the family. Physical examination with focus on the nervous system. Brain current measurement (EEG), possibly computer tomography (layered X-ray) of the head.

Since the underlying changes in the genetic material are known, a genetic examination can reliably diagnose and even predict Huntington’s disease. However, such a predictive diagnosis is rarely useful, as the disease is currently incurable and therefore no therapeutic consequences would result. If Huntington’s disease is suspected, it is certainly advisable to have a cross-sectional image of the brain taken.

Huntington’s disease is a neurodegenerative disease in which nerve cells in certain regions of the brain die off in the course of the disease. This can also be seen on the MRT images. Especially in the region that is responsible for voluntary movement, tissue atrophy can be seen.

As a result, the lateral ventricles (= cavities filled with cerebral fluid) appear dilated in imaging. This is a relatively classic finding for Huntington’s disease. However, the genetic test provides the final diagnostic certainty (see section on this).

What is the inheritance in Huntington’s disease?

Huntington’s disease is an autosomal dominant inherited disease. If a gene is inherited as dominant, this means that a defective allele on one of the two chromosomes already leads to the expression of a characteristic. The term autosomal is derived from autosomes.

All chromosomes that are not involved in determining sex are called autosomes. This means that heredity is independent of sex. It means that the defective gene can be inherited from both parents.

Men and women are therefore equally affected. In the case of Huntington’s disease, the defective gene is located on chromosome 4. Although the disease is inherited independently of the sex, it has been shown that the disease starts earlier and has a more dramatic course when the defective gene is inherited from the father.

In contrast, maternal inheritance tends to indicate a later onset of the disease. The mutated gene responsible for Huntington’s disease is located on chromosome 4 and was discovered in 1993. Since then, a genetic test has been available.

If a patient is suspected of having Huntington’s disease, a blood sample can be taken to determine whether the patient’s DNA contains this mutation. The diagnosis would then be confirmed. Even healthy people who have relatives with Huntington’s disease can have their blood tested for the mutation.

Huntington’s disease is a hereditary disease. This often has far-reaching consequences for the lives of those affected, which is why there are special guidelines for genetic tests on healthy people. For example, no minors should be tested; no genetic test should be carried out at the request of third parties (parents, partners). The detection of the gene mutation in healthy persons does not immediately lead to a diagnosis, but once a certain number of repetitions of a certain sequence in the DNA have been made, the person affected is most likely to develop Huntington’s disease.