Huntington's disease (or Huntington's chorea) is a very serious inherited neurodegenerative illness. It occurs in both men and women. It is a rare disorder, but very lethal with no efficient existing therapy.
The disease is genetically determined and it is usually transmitted from a parent to the child. The inheritance of the disease is autosomal dominant (AD). For a layman, this means that if we have a sick person, it is either because of a new mutation (rare) or by transmission of the faulty gene from a diseased parent (typical). If a sick individual has a child with a healthy partner, the child has a 50% risk of being also affected by the disease. There are no healthy carriers of the faulty gene.
Autosomal dominant genetic diseases have a tendency to disappear from the population. It's logical. A child can get the diseased gene from a sick person and the chance that an ill person gets a partner for reproduction is more or less reduced. In terms of Darwin's theory of natural selection, sick individuals are at a disadvantage when choosing a partner, they have fewer children and their disease gradually disappears from the population. The deceit of Huntington's disease is that it usually manifests in adults over 30 years of age. Until that time, the person seems to be perfectly healthy and has no problem with finding a partner and having children. This usually has destructive consequences for the affected family.
Example of a model situation: The disease has been confirmed in 30 years old man, father of two, who has a 20 years old sister. The patient's father and grandmother were also sick (both already dead). It is clear – the grandmother passed the faulty gene to he son (the patient's father) and he did the same to our patient. The question is – is the patient's sister ill? And what about the patient's children? All of them have 50% chance to have Huntington's disease as well. In addition, do we want to know? And do they want?
Note: Huntington's disease can manifest earlier, sometimes even in childhood. These cases are rare but also happen.
Scheme transmission of Huntington's disease at one affected parent
A = "sick" gene, a = "healthy" gene
Of the four possible options there are two healthy children and two sick children
as well as one of the parents (circled in red)
risk of disease transmission is therefore 50:50
Huntington's disease manifests very dramatically and tragically. The main problem is gradual neurodegeneration and deterioration of brain function. Firstly, the patient feels inconspicuous muscle twitching, which over the time gradually transforms into convulsive seizures and bizarre involuntary movements. The sick person slowly looses self-sufficiency. In addition, there is deterioration of brain cognitive functions with progressive dementia and personality changes. Swallowing disorders occur in late stages and in the end, the disease is fatal.
When Huntington's disease occurs in a family, it is possible to perform a reliable genetic test to confirm or rule out the disease in any close relative of the affected person. However, there is an ethical problem as the confirmation of the disease is a “death sentence” for a seemingly healthy young person. If a person wishes to have this test done, an examination and interview with a psychologist are highly advisable.
There is no curative therapy. The disease gradually progresses and it is inevitably fatal.