Evaluating the Role of Genes in the Development of Disease
Huntington Disease
Huntington’s disease (HD) is a neurodegenerative disorder caused by a single genetic mutation characterized by motor, cognitive, and psychiatric features. It is caused by a CAG (Cytosine-Adenine-Guanine) repeat expansion on the huntingtin (HTT) gene on the fourth chromosome (Ross et al., 2014). The mutant HTT gene contains a long abnormal polyglutamine (poly Q) sequence corresponding to the CAG genetic expansion. It exhibits toxic characteristics that result in the dysfunction and death of neurons. The disease was first discovered by George Huntington, who noted that it was a hereditary disorder characterized by chorea and psychiatric clinical features. HD is considered a genetic disease because it is caused by a heritable defect in the HTT gene inherited in an autosomal dominant manner. Do you need help with your assignment ? Get in touch with us at eminencepapers.com.
Signs and Symptoms
The main signs and symptoms of HD are motor, cognitive, and psychiatric. The motor features consist of chorea and dystonia. Chorea primarily involves involuntary and many movements that are short and usually unnecessary. In contrast, dystonia comprises persistent muscle contractions and intensified muscle tone leading to odd postures like neck turning (torticollis) or bending of the back (opisthotonos). Progression of the disease is characterized by decreased hyperkinetic, slow movements (bradykinesia), delayed initiation of motion, and dominance of rigidity.
Cognitive signs may emerge years before the onset of the disease. Impairments are associated with executive functioning (high-level processes that control the more basic cognitive functions), leading to problems in the initiation of action, organizational and planning skills, and impaired ability to react to environmental modifications. Other cognitive symptoms include slowed cognitive actions, impairment of short-term memory associated with learning difficulties, and reduced emotion recognition (Ghosh & Tabrizi, 2018).
Figure 1: Clinical Manifestations of Huntington’s disease.
Note: Huntington’s disease. (p. 2) by Bates, G., Dorsey, R., Gusella, J., Hayden, M., Kay, C., & Leavitt, B. et al. (2015). Nature Reviews Disease Primers.
The common psychiatric symptoms consist of depression, anxiety, and apathy. Apathy is commonly characterized by passive behavior, loss of interest in general activities, and difficulties in activity initiation. Other psychiatric features include the development of obsessive, compulsive thoughts and behavior that might be correlated to other emotions or thoughts and formalized behaviors with repetitive habits.
Genes and Mode of Inheritance
Autosomal dominance mode of inheritance expresses HD; therefore, the presence of a mutated gene on either allele results in the HD state. The mutation is a CAG repeat expansion at the start of exon 1 of the Huntingtin HTT gene on the short arm of chromosome four, which leads to a polyglutamine (poly Q) stretch at the N-terminus of the Huntingtin protein upon translation. Every individual carries two copies of the HTT gene, each inherited from each parent. Since HD is caused by a single mutation of the HTT gene, a child is predisposed to HD if either parent carries a copy of the mutant gene. Subsequently, the child inherits the disorder if both parents carry a mutated gene copy. The normal wild-type gene usually has 10 to 35 CAG repeats. Complete penetrance of the disease is at 40 or more repetitions, while reduced penetrance is between 36 and 39 repeats, and carriers may develop HD symptoms later in life or not at all.
Treatment
HD treatment follows drug and non-drug approaches for managing symptoms. The available medications for reducing chorea include tetrabenazine and atypical neuroleptics like olanzapine, quetiapine, and risperidone. Additionally, citalopram or other selective serotonin reuptake inhibitors (SSRIs) can be used to alleviate psychiatric symptoms like depression and anxiety. Non-drug treatment involves physiotherapies to gain balance and help the patient adapt to the environment. Language and speech therapies are also helpful in improving communication.
References
Bates, G., Dorsey, R., Gusella, J., Hayden, M., Kay, C., & Leavitt, B. et al. (2015). Huntington disease. Nature Reviews Disease Primers, 1(1). https://doi.org/10.1038/nrdp.2015.5
Dash, D., & Mestre, T. (2020). Therapeutic Update on Huntington’s Disease: Symptomatic Treatments and Emerging Disease-Modifying Therapies. Neurotherapeutics, 17(4), 1645-1659. https://doi.org/10.1007/s13311-020-00891-w
Ghosh, R., & Tabrizi, S. (2018). Huntington disease. Neurogenetics, Part I, 255-278. https://doi.org/10.1016/b978-0-444-63233-3.00017-8
Ross, C., Aylward, E., Wild, E., Langbehn, D., Long, J., Warner, J., & Tabrizi, S. (2014). Huntington disease: natural history, biomarkers and prospects for therapeutics. Nature Reviews Neurology, 10(4), 204-216. https://doi.org/10.1038/
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Question 
Evaluating Inherited Diseases
This two-part assignment will allow you to evaluate genes’ role in developing certain diseases. Additionally, you will demonstrate your ability to use electronic databases for research purposes.
Evaluating the Role of Genes in the Development of Disease
First, you will select a genetic disease. You may take this opportunity to think about your individual health and health risks and consider any genetic diseases prevalent in your family. Do you have a predisposition to breast cancer, diabetes, hypertension or any other disease? You may consider your own health risks or those of other individuals, such as a family member or friend. Then, in a paper of 750–1,000 words, address the following:
Part I: Evaluating the Role of Genes in the Development of Disease
Provide an introduction of the disease, including the reason why this would be considered a genetic/inherited disease.
Discuss the major signs/symptoms of the disorder.
Research the mode of inheritance for your chosen disease and provide a thorough discussion of the mode of inheritance. Your discussion should focus on how the disease is passed on from parent to offspring.
Are there specific genes that have been identified in the development of this disease? If so, what are they?
Discuss any available treatments used for the disease or to manage its symptoms.
Address any lifestyle changes or preventative efforts that may reduce the development of the disease or may help to manage the symptoms of the disease.
If a family member is diagnosed with this disease or is identified as a carrier of the gene that causes the disease, what steps could they take to reduce the likelihood that their children may inherit the disease?
Part II: Purdue Global Library Search