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We all have noticed that older individuals frequently forget small details like where they put their money, important documents, or other objects. However, amnesia turns seriously problematic when it affects their ability to work or interact with others. These might be symptoms of the onset of "dementia," a disorder. Although dementia primarily affects older people, it is not a necessary part of getting older. The World Health Organization estimates that more than 55 million people worldwide currently have dementia and roughly 10 million new cases yearly.
What is Huntington's Disease?
American physician George Huntington (1850–1916) is credited with describing the condition that carries his name, Huntington's disease. Huntington's disease (HD), also known as Huntington's chorea, is an inherited neurodegenerative disease. Huntington's disease is a genetic disorder caused by an incorrectly functioning gene on chromosome 4. Huntingtin is a protein that normally helps nerve cells develop, but when it is faulty, it can damage them instead, and this is most common in the part of the brain that controls movement, learning, thought, and emotion (basal ganglia and cerebral cortex). Huntington's disease is primarily thought of as a motor function disorder affecting a person's movement. However, there may be brain damage that leads to dementia. It causes a gradual, progressive deterioration in a person's movement, memory, thinking, and emotional state.
Epidemiology and Comorbidity
Huntington's disease is a rare neurodegenerative disorder characterized by chorea, behavioral manifestations, and dementia. It affects 1 in 10,000 people worldwide and is unvaryingly fatal. According to Genetics Home Reference, it appears to be less prevalent in Japanese, Chinese, and African people. Studies revealed a significantly lower prevalence of Huntington's disease in Asia than in European, North American, and Australian populations. The first signs normally appear in people aged 30–50 years. However, recent studies indicate that about 10% of cases appear after age 60 and 5-10% of cases under 18 years, also known as juvenile Huntington's disease.
Zielonka et al. (2020) have identified eight clusters of Huntington's disease comorbid conditions: musculoskeletal, allergies, cardiovascular, neurological, gastrointestinal, thyroid, psychiatric, and ophthalmologic. Among these eight clusters of diseases, psychiatric and cardiovascular events were significantly more frequent in both pre-and symptomatic Huntington's disease patients, while neurological and gastrointestinal clusters showed significantly higher occurrence in the Huntington's disease symptomatic group.
Signs and Symptoms
Signs and symptoms of Huntington's disease are usually present as a triad of motor, cognitive, and psychiatric symptoms. In the early stages, subtle personality changes, problems in cognition, physical skills, irritability, and mood swings occur, usually preceding the motor symptoms. Individual differences in the onset, progression, and extent of cognitive and behavioral symptoms are significant.
Chorea, or jerky, random, and uncontrollable movements, are the most common initial physical symptoms. It may be initially exhibited as general restlessness, lack of coordination, or slowed saccadic eye movements. As the disease progresses, signs including rigidity, writhing movements, or aberrant posture become more obvious. These are signs that the brain's system for regulating movement has been affected.
Psychomotor functions deteriorate to the point where any action requiring muscle control is compromised. Physical instability, unusual facial expressions, and difficulties speaking, chewing, and swallowing are common. Weight loss and sleep issues are also related symptoms.
Cognitive abilities deteriorate over time and eventually lead to dementia. Huntington's disease is traditionally linked to the onset of dementia. Dementia seen in this disease is the subcortical type, which has more motor abnormalities and fewer language abnormalities than the cortical type. The dementia of Huntington's disease exhibits psychomotor slowing and difficulty with complex tasks, but memory, language, and insight remain relatively in the early and middle stages of the illness. As the disease progresses, however, dementia becomes complete; the features distinguishing it from dementia of Alzheimer's type are the high incidence of depression and psychosis. Short-term memory deficits to long-term memory difficulties, including deficits in episodic, procedural, and working memory, have been reported by individuals with Huntington's disease.
Reported neuropsychiatric signs are anxiety, depression, reduced display of emotions, aggression, and compulsive behavior.
Causes of the Disorder
The huntingtin gene (HTT), which codes for the huntingtin protein, is present in two copies in each individual (HTT). Studies have found that the mutation of the HTT gene located on the short arm of chromosome 4 (4p16.3), which instructs the making of a protein called huntingtin, is responsible for Huntington's disease.
Trinucleotide repeat expansions, a short repeat that varies between people and may alter length over generations, make up a portion of the HTT gene. A dynamic mutation may increase the number of repeats if the repeat is present in a healthy gene, leading to a faulty gene. A modified version of the protein known as mutant huntingtin protein(mHTT) is produced when the length of this repetitive portion reaches a specific threshold. The different ways these proteins perform lead to pathological alterations, resulting in the disease's symptoms. The condition is caused by a mutation in either person's HTT alleles and is genetically dominant and fully penetrant.
Pharmacologic therapy is limited to symptomatic treatment. Chorea can be partially suppressed by haloperidol and olanzapine neuroleptics, benzodiazepines, or the monoamine-depleting agent tetrabenazine. Supportive care with attention to nursing, diet, and special equipment is helpful for individuals with dementia caused by Huntington's disease. Numerous social problems beset individuals with dementia due to Huntington's disease, and practical help, emotional support, and counselling can provide relief.
In genetic disorders such as Huntington's disease, Genetic counselling can provide information on the mode of inheritance and implications of genetic disorders to help individuals make informed decisions. Huntington's disease genetic testing was introduced in 1993. To treat, slow down, or prevent Huntington's disease, researchers have been exploring the potential of gene therapy. Emory University researchers proposed in 2017 that "cutting and pasting" DNA could aid in the prevention of Huntington's disease.
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