Huntington’s disease is an inherited degenerative neurological disease that leads to dementia. It is a disorder of the basal ganglia causing progressive motor incoordination, abnormal involuntary movements (chorea), and intellectual decline. Clinical features and Symptoms: Huntington’s disease usually causes movement, cognitive and psychiatric disorders with a wide spectrum of signs and symptoms. Which symptoms appear first varies greatly among affected people. During the course of the disease, some disorders appear to be more dominant or have a greater effect on functional ability.
The disease begins insidiously with restlessness, choreiform (dancelike) movements, and personality changes (irritability, depression, and occasionally psychosis). The symptoms gradually worsen, with severe involuntary, large-amplitude motions, grimacing, poor balance, and very poor fine-motor coordination. Abnormalities of eye movement also occur early in the disease and worsen with its progression; speech and swallowing are always affected. A detailed list of symptoms is outlined below. Movement disorders.
The movement disorders associated with Huntington’s disease can include both involuntary movements and impairments in voluntary movements: • Involuntary jerking or writhing movements (chorea) • Involuntary, sustained contracture of muscles (dystonia) • Muscle rigidity • Slow, uncoordinated fine movements • Slow or abnormal eye movements • Impaired gait, posture and balance • Difficulty with the physical production of speech • Difficulty swallowing Cognitive disorders Cognitive impairments often associated with Huntington’s disease include: • Difficulty planning, organizing and prioritizing tasks •.
Inability to start a task or conversation • Lack of flexibility, or the tendency to get stuck on a thought, behavior or action (perseveration) • Lack of impulse control that can result in outbursts, acting without thinking and sexual promiscuity • Problems with spatial perception that can result in falls, clumsiness or accidents • Lack of awareness of one’s own behaviours and abilities • Difficulty focusing on a task for long periods • Slowness in processing thoughts or “finding” words • Difficulty in learning new information Psychiatric disorders The most common psychiatric disorder associated with Huntington’s disease is depression.
This isn’t simply a reaction to receiving a diagnosis of Huntington’s disease. Instead, depression appears to occur because of injury to the brain and subsequent changes in brain function. After the onset of Huntington’s disease, a person’s functional abilities gradually worsen over time. The rate of disease progression and duration varies. The time from disease onset to death is often about 10 to 30 years. Juvenile onset usually results in death in fewer than 15 years. Death frequently results from secondary causes such as pneumonia( or other infections), injuries related to falls and complications due to inability to swallow.
About 10% of those affected have a rigid form of the disease in which choreiform movements are less prominent, and stiffness and slowness of movement and abnormal posturing (dystonia) are the dominant features. This variety is more likely to occur when the disease begins before the age of 20 years. Therapy is merely supportive: no medications significantly affect the course of the disease or functional capacity of the sufferer. Depression or psychosis, however, can be temporarily alleviated by antidepressant and antipsychotic medications.
A progressive intellectual decline is usually observed, but even in the late stages of the disease, patients can often recognize family members and interact with other people to a limited extent. Gene locus: The gene for Huntington’s disease has been localized at the end of the short arm of chromosome 4. The gene, termed IT15, contains a series of three nucleotides that are repeated from 11 to 30 times. On Huntington’s disease chromosomes, this triplet repeat is expanded and occurs in greater numbers (37 to over 86 repeats). The IT15 gene itself is very large (10 kilobases) and is thought to encode a protein of approximately 3144 amino acids.
The predicted protein, huntingtin, does not resemble any known protein. Inheritance of the disease: Huntington’s disease is a rare disorder that affects approximately five to ten of every 100,000 persons. Inherited as an autosomal dominant mendelian trait, which means one copy of the altered gene in each cell is sufficient to cause the disorder. An affected person usually inherits the altered gene from one affected parent. In rare cases, an individual with Huntington disease does not have a parent with the disorder, such an occurrence may be the result of a genetic mutation that happened during the fathers sperm development.
As the altered gene is passed from one generation to the next, the size of the CAG trinucleotide repeat often increases in size. A larger number of repeats is usually associated with an earlier onset of signs and symptoms. This phenomenon is called anticipation. People with the adult-onset form of Huntington disease typically have 40 to 50 CAG repeats in the HTT(IT15) gene, while people with the early-onset form of the disorder tend to have more than 60 CAG repeats. Individuals who have 27 to 35 CAG repeats in the HTT(IT15) gene do not develop Huntington disease, but they are at risk of having children who will develop the disorder.
As the gene is passed from parent to child, the size of the CAG trinucleotide repeat may lengthen into the range associated with Huntington disease (36 repeats or more). Men and women are affected equally. The average age at onset is between 35 and 40 years, but the disease can begin as early as 2 years or as late as 80 years. The disease appears to have originated in northern Europe, England, or Scandinavia. Pathologically, the nerve cells in the caudate nucleus and putamen degenerate, and although other regions of the brain are affected to a minor extent, these regions are the most seriously damaged.
Offspring of individuals suffering from the disease have a 50% risk of developing it, and can be tested by recombinant genetic technology. Mutations: The mutation rate of huntington’s disease is very low, and no confirmed new mutations have ever been reported. Juvenile huntington’s disease is a variant and can occur in individuals as young as five years of age. When huntington’s disease appears in someone under the age of 20 years, the illness is recognized as juvenile . Juvenile HD is characterized by a movement disorder which differs from that of affected adults.
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