Neurological Disorders: Huntingtons Disease

What is Huntingtons-disease?

Huntingtons disease is a hereditary, autosomal dominant type neurodegenerative disorder for which currently no curative treatment exists. A Neurologist is frequently involved in the care of these patients.

Huntingtons disease is characterized by a combination of abnormal involuntary movements (chorea), cognitive dysfunctions and behavioral changes. The disease generally starts and builds up gradually, and reaches the late stages in about 10 to 20 years and invariably fatal at this moment.

What exactly is wrong with this condition?

This disease is the result of degeneration of certain types of neurons (brain cells) in an area of the brain called as basal ganglia. However different grades of damage are also seen in other areas of brain including cerebral cortex, thalamus, cerebellum etc. The damage results in alteration of the concentration of certain neurochemicals like dopamine, acetylcholine, GABA etc.

What kinds of genetics are involved with Huntingtons-disease?

It is an autosomal dominant type hereditary disease meaning;

• Presence of disease or abnormal gene in only one parent is enough for the kids to get it

• If a parent is affected then each child has 50% chance of catching the disease
• Both male & female children of the affected parent can contract this disease

This disease belongs to a group of disease called as trinucleotide repeat disorders. A chromosome contains genes, and certain genes have areas of repetition of the same DNA bases (nucleobases) and such areas are called as nucleotide repeats. When combinations of 3 bases repeat it is called trinucleotide repeat. Huntington disease results when CAG trinucleotide repeat expands abnormally (means more repeats than the normal range). It is an example of “more than necessary is not good always”

How does patient present?

There are two types of Huntington's disease; the adult and juvenile types. About 90% are adult type, the remained up to 10% are juvenile type (also called as Westphal variant). Typical adult type presents around 30 to 45 years age while the juvenile type before 20 years.

In general these are the usual manifestations of these patients;

Chorea:

These are abnormal involuntary movements involving various parts of the body. Chorea is defined as abnormal, non repetitive, irregularly occurring and randomly distributed movements of the limbs, head/face/tongue etc in different combination. Patients with chorea may appear restless, fidgety and uncoordinated.

Cognitive dysfunction:

Initially subtle problems are seen with attention, organization etc, and gradually memory deficits appear. This can progress to cause significant dementia. The picture is typical for what we call as sub-cortical type of dementia.

Alzheimer’s disease is a typical example of cortical type of dementia where from the beginning memory & language deficits, apraxias & agnosias etc dominate the presentation. Apraxia means an inability to perform previously learned motor activity despite of having the physical ability & desire perform it. Agnosia is a loss of a person’s ability to recognize thins by using the special senses like vision, hearing, smell, taste etc while these senses themselves are intact.

Huntingtons-disease, especially in the early stages does not manifest with these presentations typical for cortical dementias, rather the attention, concentration, motivation & emotional aspects are affected initially with only milder memory impairments. However at a later stage the difference between cortical and subcortical features starts blurring.

Psychiatric/Behavioral dysfunction:

Anxiety, depression, aggression, mania, psychotic changes are frequently seen in Huntington disease patients. In the initial stages they are absent or mild, however as disease progresses they become very noticeable. Suicidal tendency and its success rate higher in patients with this condition as compared to the general population.

As the disease progresses family members and/or care givers find it difficult to manage these patients due to cognitive& psychiatric issues, and it results in institutionalization of several patients.

Diagnosis

Genetic (DNA) test is available for the confirmation of Huntingtons disease. It is a trinucleotide repeat disorder a pointed above and this genetic mutation can be demonstrated in the laboratory.

An imaging study of the brain generally shows atrophy of caudate nucleus.

Treatment

Unfortunately there is no curative treatment for Huntingtons disease as of now. Symptomatic & supportive care is given.

The chorea can be treated with following medications;

• Neuroleptics like haloperidol, risperidone etc
• Tetrabenazine
• Benzodiazepines like diazepam etc

Antipsychotic, antidepressants, antianxiety agents are used as necessary.

Patient & family counseling is necessary.



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