Huntington's chorea

Huntington's chorea
International Classification (ICD) G10

Basics

Huntington's disease is also known as "St. Vitus' dance" and is a rare hereditary disease that affects the brain and causes movement disorders, as well as changes in character and even dementia.

The onset of the disease can occur at any age, but the first symptoms usually appear between the ages of 20 and 40, but can also occur in early childhood and old age. Huntington's disease occurs at a low rate of two to eight per 10,000 people in the population.

Doctors have little leeway when it comes to treatment options and the progression of Huntington's disease. Many substances that counteract the progressive degradation of nerve cells (neuroprotection) have been subjected to tests without so far being able to record a clear effect on the course of the disease. Up to now, only the symptoms of the disease can be alleviated with the help of drugs.

Further help for those affected and their relatives is offered by corresponding self-help groups.

Causes

Huntington's disease is caused by the loss of nerve cells in certain areas of the brain. This destruction is genetically determined. However, the gene responsible for the disease is not inherited in a sex-linked manner, which means that both men and women are affected to the same extent. If a gene defect carrier has a child, there is a 50 percent risk that the child will also develop Huntington's disease.

In order to understand the development of Huntington's disease, it is necessary to take a closer look at the molecular alphabet of the genetic material (DNA). This consists of four nucleic acids: adenine, thymine, guanine and cytosine. By combining these four acids, the entire hereditary information stored in the chromosomes is created. The cause of Huntington's disease is a change in chromosome four. In healthy individuals, there is an area where the nucleic acids cytosine-adenine-guanine are repeated ten to 30 times. If this sequence is repeated more than 36 times (CAG repeats and CAG triplets), Huntington's disease develops. If between 30 and 35 CAG repeats occur, it is not possible to say exactly what effects occur.

About one to three percent of cases occur without a family history of the disease. This can either be a new mutation or one parent has 30 to 35 CAG repeats and the disease did not break out in this parent. It can often be observed that the number of repeats often increases from generation to generation. If the number of repeats is greater than 36, the disease breaks out.

The more CAG repeats there are on chromosome four, the sooner Huntington's disease breaks out and the faster the disease progresses. Huntington's disease mainly affects the cerebral cortex with the basal ganglia. The basal ganglia are large groups of nerve cells inside the cerebral hemispheres, which are necessary for the regulated course of movement.

Symptoms

The initial stage of the disease is often characterized by mental abnormalities. Those affected are more easily irritable, aggressive or disinhibited, but the loss of spontaneity or anxiety can also increase.

Characteristic movement disorders are usually sudden, involuntary movements of the head, hands, arms, legs and trunk. In the worst cases, this can lead to a prancing gait typical of the disease, which is why the disease is also called "St. Vitus' dance".

At the beginning, patients can still incorporate the exaggerated and involuntary movements into their normal movements, which is why the observer is presented with the image of exaggerated gestures.

In the later stages of the disease, the tongue and pharyngeal muscles are also affected. This results in choppy speech with suddenly emitted words. Similarly, dysphagia may occur, with the risk of swallowing and associated pneumonia.

Later, a loss of mental ability is almost unstoppable, which can lead to dementia. Consequently, in the last phase of the disease, the affected persons are completely bedridden and dependent on the help of other persons.

Symptom similarity also exists with other non-hereditary diseases, such as symptoms after an overcoming infectious disease or caused by hormonal changes during pregnancy (chorea gravidarum). In rare cases, medication, as well as the contraceptive pill and strokes in certain areas of the brain, can also be the reason for the symptoms. Circulatory disorders can be a trigger for a special form of chorea in old age. Conjecture suggests that diseases such as hyperthyroidism may also cause chorea. In contrast to Huntington's disease, however, the course of the disease is not progressive, but the movement disorder regresses after the cause has been eliminated.

Psychological symptoms, on the other hand, are excluded as triggers.

Diagnosis

If cases of Huntington's disease are already known in the family, the diagnosis can be made on the basis of the characteristic symptoms, the typical course and abnormalities in the neurological examination. To ensure a reliable diagnosis, the blood is examined for excessive repeats of the same base pairs (CAG) in a gene on chromosome four.

If there is a suspicion of an increased risk of Huntington's disease in healthy people, they can also have a laboratory diagnosis carried out. If such a suspicion exists, the physician speaks of predictive diagnostics. These diagnostic procedures can be used to say with certainty whether the person will develop Huntington's disease, but this certainty can also have an immense impact on the psyche of the person affected. For this reason, there are guidelines in place that prevent genetic testing from being performed on minors or at the request of a third party.

In order to get an accurate picture of the extent of the nerve damage, patients are usually also subjected to neurological, neuropsychological and psychiatric examinations. These examinations may only be carried out by experienced doctors or specially trained neuropsychologists.

Both computer tomography and magnetic resonance imaging can be used to determine the extent of the degeneration of individual areas of the brain.

Therapy

The causes of Huntington's disease cannot be treated. Rather, therapy aims to alleviate the symptoms. Agents such as tiapride and tetrabenazine, as well as neuroleptics, can curb the excessive, uncontrolled movements. If depressive moods exist, they can be counteracted with antidepressants from the group of selective serotonin reuptake inhibitors (SSRI) or sulpiride.

There is no officially prescribed therapy against the progressive process of Huntington's disease. In certain stages, the mental deterioration can be slowed down by the active substance memantine.

In addition to drug therapy, other measures can also help, such as physiotherapy, occupational therapy and speech therapy. This can improve swallowing and speech disorders through certain exercises. With the help of occupational therapy, the activities of daily living can be practiced and thus a longer independence can be ensured.

Due to the severe weight loss that many patients suffer from, a calorie-rich diet is essential, as being slightly overweight alleviates symptoms. A therapy that can prevent the weight loss process has not yet been developed. Although some drug approaches are already available, they are all still in the experimental stage. CoEnzyme Q10, an endogenous protein that protects cells from damage, has slightly positive effects in high doses, but overall does not affect the course of the disease.

Another agent developed specifically for Huntington's disease is ethyl icosapent, a drug developed from the fish oil component eicosapentsoic acid. This ingredient is supposed to prevent the damage of certain cell components and to achieve an increase in the performance of diseased nerve cells. However, this drug does not counteract the movement disorder.

Forecast

Since Huntington's disease cannot be cured, patients die on average 19 years after the first onset of symptoms. This average value can fluctuate, as the development of individual symptoms, as well as the tolerance and response to certain medications vary from person to person.

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