Huntingtons Disease The Problem Biology Essay

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Huntington's disease, or Chorea disorder (HD) is an incurable neurodegenerative genetic disorder. A dominant mutation on either of the two copies of a specific gene, on the chromosome 4 causes this disease. The Huntingtin gene (HTT) is present in every human which codes for the protein Huntingtin (HTT). Huntington's disease is inherited in an autosomal dominant fashion. The probability of each offspring inheriting an affected gene is 50 %( B-17) . Inheritance is independent of gender, and the gene does not skip generations. The disease attacks cells in the part of the brain called the striatum. This thus results in uncontrollable movement, emotional disturbances and loss of mental ability. Diagram of a sideview of the brain and part of spinal cord, the front of the brain is to the left, in the centre are orange and purple masses about a quarter of the size of the whole brain, the purple mass largely overlaps the orange and has an arm that starts at its leftmost region and forms a spiral a little way out tapering off and ending in a nodule directly below the main massCloser view of neuron having a large central core with several tendrils branching out some of which branche again, the core of the contains an orange blob about a quarter of its diameter

Jerky, random and uncontrollable movements are the most common physical symptoms exhibited by patients (B-17~20). Clear appearances of the symptom as the disease progresses include, rigidity, writhing motions and abnormal posturing. Psychomotor functions become impaired and any reaction that requires muscle control such as chewing, eating, swallowing and speaking are affected as well. Physical instability as well as abnormal facial expression too becomes prevalent (B-22). This disease is a fatal genetic disease and there is no cure but there are several drugs which have been tested and are used to alleviate and slow Huntington's progression. Therefore, what are the treatments available nowadays that can help in managing this disease?


Antichorea medications

Since chorea is the most severe symptoms in Huntington's patients, the three most commonly used medications to suppress it are neuroleptics, such as haloperidol and fluphenazine; benzodiazepines: clonazepam and diazepam; and dopamine depleting agents: reserpine and tetrabenazine(B-5).

Each medication has its pros and cons. Neuroleptics suppreses movement in patients which is an adverse effect when in use to treat psychotic patients but a desired effect when used to treat chorea. Therefore the most popular neuroleptic agents are the high potency drugs, which can also induce the most Parkinsonism. Haloperidol and fluphenazine are the most commonly prescribed neuroleptics (B-5). Haloperidol and fluphenazine interferes with the effects of neurotransmitters in the brain which are the chemical messengers that nerves manufacture and release to communicate with one another. It blocks receptors for the neurotransmitters (specifically the postsynaptic mesolimbic dopaminergic D1 and D2 and serotonin type 2 receptors) on the nerves (B-23). As a result, the nerves are not "activated" by the neurotransmitters released by other nerves. Haloperidol is useful in treatment of irregular spasmodic movements of limbs or facial muscles

Chemical structure of xenazineC:\Users\User\Pictures\800px-Fluphenazine_structural_formulae.pngC:\Users\User\Pictures\638px-Clonazepam.png

Clonazepam Tetrabenazine Fluphenazine

Figure 3: Chemical structures of a few antichorea drugs

Compared to other high potency drugs, Risperidone is a newer neuroleptic which causes less Parkinsonism but is still useful in suppressing chorea and reducing agitation. Benzodiazepines, such as clonazepam and diazepam are also very useful in the treatment of chorea. Benzodiazepines generally act as a central nervous system depressant. Clonazepam and diazepam are favored because they require less frequent dosing and provide more even coverage of symptoms throughout the day. They are also less likely to precipitate withdrawal symptoms if a dose is missed (B-2,5).

Dopamine depleting agents; reserpine and tetrabenazine are also widely used. Reserpine functions by depleting norepinephrine and epinephrine, which in turn depress sympathetic nerve functions (B-4, 22). Tetrabenazine helps reduce jerky movement of Huntington's disease by increasing the amount of dopamine available in the brain especially in the basal ganglia part of the brain which is responsible for movements.

Among all, tetrabenazine is found to be the most effective drug (B-1). The efficacy of tetrabenazine as a treatment for the chorea of Huntington's disease was established primarily in a randomized, double-blind, placebo-controlled multi-center trial (Study 1) conducted in ambulatory patients with a diagnosis of Huntington's disease.Figure 1. Mean +/- s.e.m. Changes from Baseline in Total Chorea Score in 84 HD Subjects Treated with Tetrabenazine (n=54) or Placebo (n=30)

Figure 4. Mean +/- s.e.m. Changes from Baseline in Total Chorea Score in 84 HD Subjects Treated with Tetrabenazine (n=54) or Placebo (n=30)

As shown in Figure 4, Total Chorea Scores for subjects in the drug group declined by an estimated 5.0 units during maintenance therapy (average of Week 9 and Week 12 scores versus baseline), compared to an estimated 1.5 units in the placebo group. (B-3)

Tetrabenazine does not only help to alleviate chorea but at the same time can act as mood stabilizers. However it is not advisable to be used for any one in depression and those having suicidal thoughts which most of Huntington's patient more or less develop when the disease progresses (B-1). Nevertheless, not all patients respond the same way to tetrabenazine.

Huntington's is a chronic disorder and is incurable and thus will eventually lead to death. Treatments are just to alleviate symptoms and also slow the progress of the disease. Overtime, patients' survival rate decreases as the symptoms progress.

Overview chart

Figure 5: According to the study, the survival of HD decreases to below 50% after 18 years and reaches 0% survival by 39 years. (B- 5)


The problem with Huntington's is that the symptom onset isn't until people are in their late 30's or early 40's. By that age, many of them have children, meaning they've passed this deleterious gene to the next generation already, condemning them to a slow death. The social problem here is that many children are condemned to watch their parents die a painful death and knowing that they are probably headed the same way in years to come. This is a harsh reality to many of them. Also some of these people who die of Huntington's are taken out of the workforce in the prime of their careers. These are due to the involuntary movements that they develop as the disease progresses and also due to the side effects of the drugs they take. Huntington's patients also gradually lose control of their emotions and they develop abnormal facial expression which normally affects their social life. For many sufferers and their families these symptoms are the most distressing aspects of the disease. Moreover, Huntington patients tend to be suicidal. Some commit suicide because they cannot accept the fact that they will be dying a slow, painful and humiliating death while some attempt suicide due to side effects from medications which are quite difficult to tolerate. (B-6)


Figure 5: increased rate of suicide among patients with Huntington's disease.(A-6)

Worse yet, their care later into the disease are expensive. Drugs such as clonazepam as well as tetrabenazine are very expensive. Patients too will be needing treatment due to other complications that arise as the disease progresses which might need hospitalization and also tender care. These involve high cost and cause a huge financial burden and economic impact.

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Combinations of drugs are effective as it delays the progress of the disease. These delays deaths as well as increases the qualities of life of Huntington patients as their symptoms are under control. (A-7) These are proven by the study which showed that combination of fluxetine and clonazepam decreased the level of depression as compared to using single drugs.C:\Users\User\Pictures\af7f1.jpg

Figure 6: Scores on the Hamilton Depression Rating Scale Over 8 Weeks for Patients Taking Clonazepam Plus Fluoxetine or Placebo Plus Fluoxetine

However, every treatment given always comes with a setback, the side effects. Drugs used to manage Huntington's can cause a lot of adverse effects. One of it is tardive dyskinesia, which causes involuntary movement mainly in the face and mouth that arises in some patients taking neuroleptics. It is of concern as it is very hard to identify in Huntington's patients and are usually permanent. Another serious problem is neuroleptic malignant syndrome characterized by acute onset of rigidity, delirium and fever which is most frequently accompanied by leukocytosis and elevated CPK.Families should be aware of this so that the patient can be given immediate medical attention if it develops.



Starting Dose

Maximum Dose

Adverse Effects



0.5-1 mg/day

6-8 mg/day



dystonia, akathisia,



dry mouth,

weight gain


0.5-1 mg/day

6-8 mg/day



0.5-1 mg/day

6 mg/day

less parkinsonism



0.5 mg/day

4 mg/day

sedation, ataxia,

apathy, withdrawal



1.25 mg/day

20 mg/day


Dopamine Depleting Agents


0.1 mg/day

3 mg/day




25 mg/day

100 mg/day

less hypotension

TABLE 3: Medications Used to Supress Chorea and its side effects (B-5)

Through proper administration and supervision, TBZ treats the symptoms well and is considered safe although side effects such as drowsiness, slowness of movement (Parkinsonism), mood changes (depression), and nervousness/anxiety/ restlessness (akathisia) is present. The labeling for the TBZ (Xenazine) draws special attention to potential depression and suicidality. (B-7) The side effects of TBZ are reversible and are usually controlled by reducing the dose. Most importantly, there is also no evidence that TBZ induces tardive dyskinesia which gives it a distinct advantage over other dopamine-blocking agents (typical neuroleptics) in treating a variety of hyperkinetic movement disorders. It is crucialt that patients as well as their caregivers are well aware of the medications being administered as side effects may vary for individuals.


Speech therapy

Huntington's disease causes speech difficulties, affecting ability to express complex thoughts. Communication difficulties can be overcome with the help of a speech language therapist.The SLP can be helpful at all stages of the disease and normally in early stages, they aid with problem solving and developing strategies to help people with HD handle some of the problems they might be experiencing (A-1~3). The SLP can help to preserve and maintain a person's highest level of communication as the disease progresses. The SLP can also assess a person's ability to use augmentative or alternative communication (AAC) devices and techniques, which can be as simple as an electronic device that speaks for the person and then they begin to focus on personalizing the technique or method of communication. (B-9)

Physical therapy

Beginning a fitness program early in the disease process not only serves to maintain physical function, but also helps to reduce some of the stress associated with catastrophic illness(A-6~7). A routine fitness program can also be very helpful in treating depression.Physical therapy can help keep muscles strong and flexible, reducing the risk of injury by strengthening exercises for muscles involved in postural control and najor muscle groups in the body. Physical therapy also helps with balance and aerobic activity helps in enhancing cardiovascular function.

Supportive psychotherapy

Alexander Lowen,

Mind, spirit and soul are aspects of every living body. A dead body has no mind, it has lost its spirit, and its soul has departed... When your body loses some of its tend to withdraw ... illness has [this] affect ... [you] sense the world as at a distance or see it as through a haze. (B-15)

Patients normally get depressed when they get to know about their disease. Psychologists help them to live through it as well as encourage them not to give up. Psychologist normally advise them on what to do when they have bad mood swings and also help the patients through the depression they are going through. Family members and caregivers too might be involved in the process as they are enlightened about patient's sensitivity. (B-12)

Occupational therapy

As the disease progresses, occupational therapy can aid you with carrying out everyday routines, such as eating and dressing. An occupational therapist helps the person with HD and family members develop compensatory strategies.A person with HD learns to have some control over the disease and is therefore less apt to feel helpless if the strategies are starts early. Occupational therapy normally deals with memory strategies (e.g. Offer hints, aid in retrieval of information), sequencing tasks as well as concentration. People with HD are often not able to change position voluntarily although they appear to be moving all the time, and therefore are susceptible to skin breakdown from constant shearing movement. The occupational therapist normally suggests to caregivers a routine of position changes. They also can help in designing a protective environment for a person with a lot of choreic movement. Padding of hard furniture, wheelchair parts and sharp corners helps to prevent injury from falls. (B-10)


Tetrabenazine has been found to reduce choreic movements as well as reduce hypotension from reference to (B-19) and also other sources as well as the extracts

"Tetrabenazine was well tolerated and produced long-term improvement of motor symptoms in Huntington disease patients, although a slight reduction of benefit occurred during the course of treatment" by Marsha L. Miller, Ph.D.

"Neuroleptic drugs like haloperidol (Haldol) are currently in widespread use in the United States to suppress chorea, but the effect of these drugs on chorea has never been studied in a systematic way, and they have a number of troublesome side effects, such as blunting of personality, loss of voluntary movement, and hindering balance," lead author Frederick J. Marshall, MD, from the University of Rochester Medical Center in New York, said in a news release. "Our study showed that tetrabenazine, when appropriately dosed, can decrease chorea without causing those side effects. (B-21)

These articles have gone through all the stages ensuring that they are valid and address the complication with research progression. Besides the source was obtained from the study done by Huntington's Disease Society of America, the Hereditary Disease Foundation, the Huntington Society of Canada, and the High Q Foundation. The other resource that I found is in (B-3). It is very reliable and useful as it clearly indicates that the drug tetrabenazine reduces choreic movements very effectively. This too is supported by the fact in (A-7) "Tetrabenazine works by depleting dopamine levels in the brain," said Joseph Jankovic, M.D., Professor of Neurology and Director of the Parkinson Disease Center and Movement Disorder Clinic at BCM. "In 1979, I was granted special permission from the FDA to treat patients with the drug. Since that time, I've treated thousands of people with tetrabenazine and have seen amazing results that translated into marked improvement in the quality of life. . In December 2007, an independent advisory committee concluded that TBZ is effective and safe and unanimously recommended to the FDA an approval of TBZ (Xenazine) for the treatment of chorea associated with Huntington disease, which was finally granted on Aug. 15, 2008. (2457 words)