Huntington's disease: Genetics, Symptoms, Diagnosis & Treatments

Huntington's disease, Symptoms, Treatment, Diagnosis, Genetic and Neurological basis.
Huntington disease is a rare genetic disease that can give rise to involuntary movements like Huntington chorea.
Today, we’ll explore the genetic basis of Huntington disease and the Neurological basis of chorea.
• This is the short arm of chromosome 4. It is the home of the Huntington gene which codes for the Huntington protein. All humans have two copies of this gene. It has a section called trinucleotide repeat, which is a sequence of three DNA bases, Cytosine, Adenine, and Guanine, repeated multiple times.
• A mutation in this gene can further increase the repeat count. If the repeat count is over 40, this will result in a very long Huntington protein called mutant Huntington protein. It can increase the decay of certain neurons in the brain.
• This gene is inherited as autosomal dominant. You get two copies of the gene from each parent. But since it’s dominant, one mutant copy is enough to give you the disease.
• The other important feature is its penetrance close to one hundred percent.
o It means that almost all the people with the mutant gene will develop the disease.
Symptoms typically arise after the age of 35-44. The age of onset depends on the number of the repeat count of the mutation. Symptoms may arise in the childhood itself if the repeat count is very high.
At first, they develop cognitive changes and mood changes like depression.
Later, the patients will develop speech and swallowing difficulty.
Finally, they will develop jerky, uncontrollable dancing like movements called chorea.
The brain learns and stores different motor patterns in the cerebral cortex. A structure called basal ganglia keeps these motor patterns switched off via a pathway called the indirect pathway. When you want to initiate a certain movement, the motor cortex signals the basal ganglia to activate the specific motor patterns. Activation occurs via a pathway called the direct pathway. In Huntington's disease, neurons in the indirect pathway are decayed. Therefore the brain loses the ability to switch off the motor patterns. This results in uncontrollable movement such as chorea.
The presence of symptoms and positive family history is used to come to a clinical diagnosis. Genetic testing can confirm if an adult or an embryo carries the mutant Huntington Gene.
At the moment, there’s no cure for Huntington disease Drugs such as antipsychotics are given to control the movement. Supportive care includes occupational therapy, nutritional support and speech and language therapy. A new clinical trial tests a gene silencing drug to slow down the disease progression. But the hope for a complete cure is gene editing. Let’s hope the mankind will reach there soon.

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