7.5 Additional Reading:Huntington’s Disease
Huntington’s disease（HD）is an inherited condition that causes progressive degeneration of neurons in the brain.HD has a broad impact on a person’s functional abilities and usually results in movement，thinking（cognitive）and psychiatric disorders.It is caused by changes（mutations）in the HTT gene and is inherited in an autosomal dominant manner.
Signs and symptoms may include uncontrolled movements，loss of intellectual abilities，and various emotional and psychiatric problems.People with HD usually live for about 15 to 20 years after the condition begins.When HD develops early，symptoms are somewhat different and the disease may progress faster.
Treatment is based on the symptoms present in each person and may include various medications.Medications are available to help manage the symptoms of HD.But treatments can’t prevent the physical，mental and behavioral decline associated with the condition.
Signs and symptoms
Signs and symptoms of HD most commonly become noticeable between the ages of 30 and 50 years，but they can begin at any age，and present as a triad of motor，cognitive，and psychiatric symptoms.In 50%of cases，the psychiatric symptoms appear first.Their progression is often described in early stages，middle stages，and late stages with an earlier prodromal phase.In the early stages，subtle personality changes，problems in cognition，and physical skills，irritability，and mood swings occur，all of which may go unnoticed，and these usually precede the motor symptoms.Almost everyone with HD eventually exhibits similar physical symptoms，but the onset，progression，and extent of cognitive and behavioral symptoms vary significantly between individuals.
The most characteristic initial physical symptoms are jerky，random，and uncontrollable movements called chorea.Many people are not aware of their involuntary movements.Chorea may be initially exhibited as general restlessness，small unintentionally initiated or uncompleted motions，lack of coordination，or slowed saccadic eye movements.These minor motor abnormalities usually precede more obvious signs of motor dysfunction by at least three years.Such symptoms as rigidity，writhing motions，or abnormal posturing appear as the disorder progresses.These are signs that the movement function in the brain has been affected.Psychomotor functions become increasingly impaired，such that any action that requires muscle control is affected.Common consequences are physical instability，abnormal facial expression，and difficulties chewing，swallowing，and speaking.Sleep disturbances and weight loss are also associated symptoms.Eating difficulties commonly cause weight loss and may lead to malnutrition.Juvenile HD generally progresses at a faster rate with greater cognitive decline，and chorea is exhibited briefly，if at all；the Westphal variant of slowness of movement，rigidity，and tremors is more typical in juvenile HD，as are seizures.
Cognitive abilities are progressively impaired and tend to generally decline into dementia.Especially affected are executive functions，which include planning，cognitive flexibility，abstract thinking，rule acquisition，initiation of appropriate actions，and inhibition of inappropriate actions.As the disease progresses，memory deficits tend to appear.Reported impairments range from short-term memory deficits to long-term memory difficulties，including deficits in episodic（memory of one’s life），procedural（memory of how to perform an activity），and working memory.
Diagnosis
Diagnosis of the onset of HD can be made following the appearance of physical symptoms specific to the disease.Genetic testing can be used to confirm a physical diagnosis if no family history of HD exists.Even before the onset of symptoms，genetic testing can confirm if an individual or embryo carries an expanded copy of the trinucleotide repeat（CAG）in the HTT gene that causes the disease.Genetic counseling is available to provide advice and guidance throughout the testing procedure and on the implications of a confirmed diagnosis.
Management
Treatments are available to reduce the severity of some of HD symptoms.As the disease progresses，the ability to care for oneself declines，and carefully managed multidisciplinary caregiving becomes increasingly necessary.Although relatively few studies of exercises and therapies have shown to be helpful to rehabilitate cognitive symptoms of HD，some evidence shows the usefulness of physical therapy，occupational therapy，and speech therapy.
There is currently no cure for HD and no way to slow or stop the brain changes.Current treatments focus on managing symptoms.The following treatments are used as first-line strategies for three of the disorder’s most troubling symptoms：(https://www.daowen.com)
Chorea（involuntary movements）：The U.S.Food and Drug Administration（FDA）has approved tetrabenazine and deuterabenazine to treat chorea associated with Huntington’s.Antipsychotic drugs，such as olanzapine，may also be used to ease chorea.
Irritability：For severe anger and threatening behavior，experts agree that an atypical antipsychotic drug is the preferred approach.For less severe，nonthreatening irritability，experts recommend first trying a selective serotonin reuptake inhibitor（SSRI），a type of antidepressant.
Obsessive-compulsive thoughts and actions：Experts also recommend SSRIs as the standard treatment for these symptoms.
Other symptoms of HD，such as anxiety，depression and insomnia，should also be treated.Due to the complexity of the disease，effective treatment of symptoms may be a lengthy process，and may include several approaches with different drugs and doses.
Prognosis
Life expectancy in HD is generally around 20 years following the onset of visible symptoms.Most life-threatening complications result from muscle coordination，and to a lesser extent，behavioral changes induced by declining cognitive function.The largest risk is pneumonia，which causes death in one third of those with HD.As the ability to synchronize movements deteriorates，difficulty in clearing the lungs and an increased risk of aspirating food or drink both increase the risk of contracting pneumonia.The second greatest risk is heart disease，which causes almost a quarter of fatalities of those with HD.Other associated risks include choking，physical injury from falls，and malnutrition.
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Task 9 Identify the word elements and define the meaning of each medical term.
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