Huntington’s Disease, Term Paper Example

Huntington’s disease has been traced back to the middle ages and had been described by many individuals. It was initially named as “chorea” which was derived from the Greek word meaning “dance”, mainly attributed to the movement made by people with the disease. Individuals afflicted with the disease often make involuntary and uncontrollable jerking and writhing movements. It was not until 1872 that the first complete description of the disease was put forth by George Huntington. Huntington’s disease is a neuro-degenerative disorder that largely affects cognition and muscle coordination. Psychiatric problems are also associated with the disease. Huntington’s is characterized by involuntary muscle movements called chorea, accounting for its previous name Huntington’s chorea. Those of Western European lineage are more predisposed to the disease compared to Africans or Asians. Throughout the world, Huntington’s affects 5-10 people per 100,000, with similar prevalence rates for both men and women (Sharon et al., 2010).

Genetics

The Huntingtin gene (HTT) is present in all mammals. A large portion of HTT can be found in the brain and testes while the heart, lungs and the liver contain moderation portions of HTT. The primary role and function of HTT within the human body is still unclear although its ability to interact with proteins that are involved during the transcription, cell signaling and intracellular transport has been established. Conversely, the mutated Huntingtin gene (mHtt) is particularly toxic to some types of cells, particularly the nerve cells in the brain, thus accounting for problems in movement, coordination, mood and other cognitive functions such as memory.

Huntington’s disease is characterized by a genetic defect on chromosome 4. The Huntingtin gene or HTT has a typical sequence comprising of cytosine-adenine-guanine (CAG) that is repeated several times and results in the production of the polyglutamine tract (Walker, 2007). In a normal person, this repetition of the CAG sequence occurs at a rate of 10-28 times. However, a repetiion of the CAG sequence at a rate of 36 times and higher indicates a mutation of the Huntingtin gene, referred to as mHtt. Additionally, the number of the repeating CAG increases as the disease is passed on throughout the generations. This results to an increased chance of developing symptoms and getting the disease at an early age. Due to this, symptoms of Huntington’s disease can present in predisposed family members during their early years.

Huntington’s is autosomal dominant, meaning that individuals with a parent afflicted with Huntington’s disease has a 50% chance of getting the Huntington gene, they can become afflicted themselves at any point in their lifetime and they can pass the same gene to their children. Huntington’s usually present in two forms: (1) Adult-onset Huntington’s disease, the most common form of Huntington’s and presents in individuals aged 30 to 40 years, and (2) Early-onset Huntington’s disease, which is less common and symptoms start during childhood or early adolescence.

Signs/Symptoms

The pressing signs and symptoms of Huntington’s disease vary from one individual to the next. However, practitioners commonly note that early appearance of symptoms often signify faster progression of the disease. The first stage of Huntington’s disease is often depicted by uncontrollable movements and psychological changes. Uncontrollable movements may include stumbling, jerking, writhing, general clumsiness, and tripping. These movements are often signs of “chorea”, and it generally intensifies during periods of anxiety. Meanwhile psychological changes can present as memory loss or forgetfulness, inability to concentrate or focus, mood swings, irritability, and apathy. Halfway through the course of the disease, initial symptoms become more pronounced and easily noticed even by a casual observer. In some cases, the degree of symptoms may worsen and people with Huntington’s disease become hostile with violent outbursts or they may experience severe bouts of depression. The ability to focus, make decisions, learning and other such intellectual tasks become increasingly more difficult as the disease progresses. During the end stage of the disease, symptoms can cause enough damage that requires individuals affected with Huntington’s disease to require full time care or institutionalization. Although a majority of individuals at this stage of the disease remains aware of their environments and are able to understand and express their emotions, vital functions continue to decline. People at this stage often exhibit loss of the ability to speak, eat, and swallow. Most individuals will also be unable to walk or may have severe problems in maintaining balance.

Diagnosis

Huntington’s disease is often diagnosed after the appearance of significant signs and symptoms that are particular to the disease (Walker, 2007). A physical and psychological examination may be undertaken during the initial diagnosis phase in order to determine if the disease has started. People often seek consultation commonly after noticing signs of chorea or involuntary movements and psychological symptoms are rarely the cause prompting consult as they are often recognized during the later part of the disease. The UHDRS or Unified Huntington’s Disease Rating Scale was developed as an assessment tool to appraise the relevant domains affected by Huntington’s disease, namely: motor function, cognitive function, behavior irregularities/ abnormalities and independence and the individual’s functional capacity (HSG, 2009). Imaging tests can also be utilized as degeneration of the caudate nuclei can indicate the early phase of Huntington’s disease while cerebral atrophy can indicate an advanced stage. Brain activity is also assessed through PET scans and FMRI prior to the appearance of physical symptom and changes in brain activity can indicate Huntington’s disease. However, these imaging studies are largely experimental and do not fully confirm the diagnosis of Huntington’s disease.

Huntington’s disease is largely hereditary and passed on from one generation to the next. Due to this fact, individuals who face the risk of acquiring the disease attempt to seek early diagnosis. Early diagnosis of Huntington’s disease is made possible by genetic testing, which can be achieved by obtaining a blood test. The test consists of identifying if the faulty gene is indeed inherited and counting the CAG repeats (Myers, 2004). However, genetic testing is merely identifying the inheritance of the faulty gene and a positive result does not equate to a diagnosis of Huntington’s disease. Individuals with positive results from the genetic test may still be healthy and the onset of Huntington’s disease cannot be estimated. Meanwhile, a negative result from the genetic test indicates that the faulty gene was not inherited and there is no risk in developing Huntington’s disease. Prenatal testing is also available to pregnant women by obtaining a sample of the chorionic villi from the fetus and operates on the same principle as genetic testing. The mother can have the option of terminating the pregnancy if the fetus carries the faulty gene (Kuliev & Verlinsky, 2005).

Despite the availability of genetic testing for Huntington’s disease, over 95% of individuals with a family history of Huntington’s or at risk of acquiring the disease choose not undergo any type of test. This refusal to obtain the test is largely attributed to the fact that there is no available treatment or cure for Huntington’s. It is undeniable that undergoing genetic testing is a personal decision and can be life-changing. However, the impact of a positive result is also great. It has been found that individuals have an increased predisposition to commit suicide after obtaining a positive result (Walker, 2007). On the other side of the spectrum, individuals who tested negative can experience guilty feelings for having eluded the disease or outlive other family members with the condition. In this regard, genetic counseling is highly recommended as counselors can provide the necessary information, psychological support and essential advice for people who choose to undergo testing (Burson & Markey, 2001).

Management

Up to now, there is no cure for Huntington’s but research into the subject has brought about a variety of treatment options in order to decrease and control the severity of symptoms. Due to the functional decline caused by Huntington’s, individuals benefit from a wide range of therapies such as physical therapy to manage physical symptoms associated with the disease. An initial goal during rehabilitation includes maintaining functional capacity and preventing loss thereof (Quinn & Busee, 2012). An exercise or treatment plan can be implemented in order to maintain strength and physical fitness. Physical therapy also allows assessment of ability to walk and risk for falls. Consequently, preventive measures can be established and necessary interventions can be implemented. Another major characteristic of the disease include loss of the ability to speak and swallow. Due to this, managing diet and nutrition is a big concern as individuals with Huntington’s experience weight loss secondary to impaired swallowing. Referral to a speech and language therapist can facilitate in assessment of ability to swallow and implementation of guidelines that would ensure safety during eating or feeding. Impaired swallowing is commonly managed through the use of thickening agents that are mixed onto the liquid to assist individuals to safely swallow foods or liquids. Alternatively, therapists may implement guidelines on the consistency and type of foods that an individual is allowed to take in based on their assessment. Meanwhile, individuals who are deemed to be unable to swallow have the option of using a feeding tube. The person will have to undergo the procedure of percutaneous endoscopic gastrostomy in a hospital wherein a feeding tube is inserted into the stomach. This allows the delivery of adequate nutrients directly to the stomach and a dietician can provide information and advice to manage nutrition (Panagiotakis et al., 2008). For the treatment of chorea, the drug Tetrabenazine is the only approved drug by the FDA for this purpose (USFDA, 2008). Tetrabenazine acts by reducing dopamine levels that can reach the nerve cells within the brain. However, a major side effect of Tetrabenazine is depression, and as such, is contraindicated to people with untreated depression or those with suicidal tendencies. Similarly, anti-psychotic drugs can also alleviate chorea in addition to controlling psychological symptoms of the disease such as delusions, violent outbursts and hallucinations. On the other hand, Anti-psychotics can aggravate dystonia, characterized by muscle stiffness and rigidity. Other side effects of anti-psychotics include sedation and tremors.

References

Burson, C.M & Markey, K.R. (2001). Genetic counseling issues in predictive genetic testing for familial adult-onset neurologic diseases. Semin Pediatr Neurol 8 (3): 177–86.

Kuliev, A & Verlinsky, Y. (2005) Preimplantation diagnosis: A realistic option for assisted reproduction and genetic practice. Curr. Opin. Obstet. Gynecol. 17 (2): 179–83.

Myers, R.H. (2004). Huntington’s Disease Genetics. NeuroRx 1 (2): 255–62

Panagiotakis, P.H. et al. (2008). DPEJ tube placement prevents aspiration pneumonia in high-risk patients. Nutr Clin Pract 23 (2): 172–5.

Quinn, L. & Busee, M. (2012, February). Development of physiotherapy guidance and treatment-based classifications for people with Huntington’s disease. Neurodegenerative Disease Management 2 (1): 21–31.

Sharon, I. et al. (2010). Huntington Disease Dementia. Medscape. Retrieved from http://emedicine.medscape.com/article/289706-overview

The Huntington Study Group (2009). Unified Huntington’s Disease Rating Scale (UHDRS). UHDRS and Database. Retrieved from http://www.huntington-study-group.org/Resources/UHDRS/tabid/67/Default.aspx

US Food and Drug Administration (2008, August). FDA Approves First Drug for Treatment of Chorea in Huntington’s Disease. Retrieved from http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2008/ucm116936.htm

Walker, F.O. (2007). Huntington’s disease. Lancet 369 (9557): 218