Huntington’s disease is a hereditary neurodegenerative disorder, characterized by the appearance of motor, cognitive and psychiatric symptoms. Debuts around 30 or 40 years, with a more or less rapid progression towards death.
The other name that this disease receives is “Huntington’s chorea” the latter term refers to the type of typical motor disorders of the disease, choreic movements.
How is Huntington’s disease inherited?
Huntington’s disease is inherited in an autosomal dominant way; that is, the altered gene” has more strength” than the unaltered gene. Thus, it will only be necessary to inherit a defective copy from one of the two parents to develop the disease.
On the other hand, the term “autosomal” indicates that the alteration is not found in the sex chromosomes. In fact, the genetic alteration responsible for the disease is on chromosome 4. To better understand this, the following example is presented:
In a couple formed by a man with Huntington’s disease, and a woman without this disease, she will have two copies of the normal gene, while he will have mutated at least one of the two.
What will happen if they have a child? There will be a 50% chance that the healthy gene from the father will join the mother’s one. In this case, the child will not inherit the disease. And, on the other hand, there will be a 50% chance that the child inherits the mutated gene. In these cases, the disease will develop.
It should be noted that in Huntington’s disease, penetrance is about 95%. This implies that practically all people who have a mutated allele develop the symptoms of the disease.
What is the cause?
The visible consequences of chromosomal inactivation
Is due to the abnormal expansion of the CAG trinucleotide, in the Huntingtin gene, located on chromosome 4. In most cases, up to 39 copies are produced, this being indicative of the disease. The mutation leads to the appearance of a mutant huntingtin protein, which causes neurological damage both directly and indirectly.
Evolution of Huntington’s disease
Normally, the disease begins between 30 and 40 years in most cases. Even so, there are cases in which the disease develops in childhood or in youth. On the other hand, there is also evidence of cases of development of the disease in people over 55 years of age. In sum, the age at which the first symptoms appear is variable.
Huntington’s chorea evolves slowly, but inexorably, towards death. During their progression, one type of symptoms or others may predominate, depending on the person.
Initial clinical manifestations
The first clinical manifestations are not particularly striking. It may appear insomnia, restlessness, anxiety and even small alterations in behavior. The erratic movements of hands and feet are typical of this stage (sudden hits to objects) and the tremors.
Progression of the disease
As the disease progresses, motor symptoms are becoming more and more pronounced, and increasingly difficult to control.
- Choreographic movements. These are involuntary movements of the extremities, neither rhythmic nor regular, although they may vaguely recall “dancing”. They worsen over time, incapacitating the person for the development of their daily activities.
- Bradicinesia. Slowness to initiate and develop voluntary movements.
- Dysarthria. It is called the difficulty to articulate words and sounds.
To these problems, alterations at the cognitive level and psychiatric alterations are added. On the one hand, at the cognitive level, various functions can be altered. Among other problems, include:
- Language disorders. With difficulty to repeat, nominate, form complex sentences. These problems, as well as motor disorders, begin very slightly, almost imperceptibly, to progress.
- Alterations in the capacity of organization, of execution of tasks. There are also problems to recognize and process emotions from others and their own
- Difficulty for spatial orientation Being relatively frequent that the patients hit against objects (corners, tables, etcetera).
Finally, psychiatric disorders are almost a constant, may be present even before the first symptoms of the disease manifest. Among these, the anxiety and depression, mainly associated with the progression of the disease. You can also see pictures of psychosis, apathy…
Final phase of the disease
In the final phase of the disease, there is a total loss of functionality. Patients with Huntington’s disease in the final stages need 24-hour care. At this point, the patients are unable to communicate or even think, except brief moments of lucidity.
Although the chorea in these cases usually has disappeared, it is replaced by rigidity and bradykinesia. They need support to feed themselves, bladder catheters, among others. In this point, the risk of aspiration pneumonia it is very high. Normally, death comes from complications arising from the disease or suicide.
The diagnosis of the disease, as in others, should be made based on an interview with the patient, with physical examination (with special attention to neurological examination). At the same time, an evaluation of the clinical history must be made, especially the family history.
On the other hand, it is necessary to perform a psychiatric evaluation This will help the doctor to explore in greater depth the psycho emotional health of the patient and determine possible difficulties.
In addition, it is necessary to carry out genetic studies. They should be performed if the patient shows typical motor symptoms of the disease. The result of these tests should be informed to the patient, recommending also inform the family, given the implications.
Currently, there is no treatment to cure the disease. The treatment is intended to act on the symptoms and improve the quality of life of these patients. In this sense, it is fundamental that both patients and their relatives and caregivers receive Psychological Support.
To treat movement problems, drugs such as tetrabenzain are used, that reduces choreic movements; however, it can worsen psychiatric disorders. To treat the psycho-emotional aspects of the patient, the following are used:
- Stabilizers of the mood
- Among other medications.
It should be noted that some drugs, such as haloperidol, also have effects on movement disorders.
Research in progress
In the last 20 years there have been almost 100 clinical trials with more than 49 different active ingredients. However, less than 4% of these trials showed promising results.
To this day, it is possible that the most promising results come from the hand of directed therapy against the DNA or RNA of the mutant protein originated in the disease.