SciTech

Health Talk: Huntington's disease

Nearly 25,000 Americans suffer from Huntington’s disease, so they cannot control their own actions and are unable to make their own decisions. The statistics for the disease, as reported in an article in The New York Times, also show that nearly 75,000 people carry the mutant gene responsible for the disease and are largely unaware of having the disease until its symptoms start showing up, which is usually around middle age. The symptoms of this genetic disorder are due to the wasting of neurons, or loss of nerve cells, in the brain.

The disease is named after the American physicist George Huntington, who first described it in 1872. Sometimes, the disease is also called Huntington’s chorea because in Greek, the word chorea means “dance,” and dance describes the jerky, involuntary, and uncontrolled movements that characterize the disease. The disease is a neurodegenerative disease in which the cells of the brain and spinal cord are lost.
These cells have different functions that include controlling movements, making decisions, and processing sensory information.
Huntington’s disease is a genetic disorder caused by a mutation in the Huntington gene. In this disorder, the length of the Huntington gene exceeds its normal range.

The Huntington gene normally consists of a sequence with repeats of multiple units of three bases — CAG. This is a trinucleotide repeat representing the amino acid glutamine. The resultant chain with the repeats is called a polyglutamine or polyQ tract. A chain with more than 36 glutamines results in Huntington’s disease because, in this case, the rate of decay of medium spiny neurons, which are cells in the brain that are responsible for controlling body movements, increases.
If a person has a faulty gene for this disease, there is a 50 percent chance that their offspring will have the defect as well. But, if the offspring does not inherit the disease, it cannot be passed on to future generations. Children rarely develop the symptoms of the disease. When the symptoms do develop in young people, though, they suffer severely and their symptoms progress very quickly. The disease is classified as juvenile Huntington’s disease in this case.

The initial signs of Huntington’s disease are decreased cognitive abilities and personality changes. People suffering may show signs of depression or get irritated or angry. It may also become hard for them to answer questions and make decisions. They may not remember important information and may become forgetful. The patient is usually unaware of the changes due to the disease and may notice them quite late, often after family and friends become aware of these changes.
The physical signs of this genetic disorder include clumsiness, mild balancing problems, and involuntary facial movements, like grimacing. As the disease progresses, the whole body may exhibit sudden jerky, involuntary movements with severe balancing problems. It becomes very hard for the person to coordinate his or her movements and to shift his or her gaze without moving the head. The suffering person may have slurred speech and swallowing problems. Often, these physical problems are accompanied by dementia.

The severity of the disease in young people can be explained by the fact that their symptoms are similar to those of Parkinson’s disease and include tremors, slow movements, and muscle rigidity. As described on Mayoclinic.com, those who acquire the disease very early in their lifetimes may even have seizures. These symptoms develop slowly over a long period of time. The degree of nerve waste, or nerve cell loss, determines the severity of the symptoms. Usually, the patient succumbs to the disease 10 to 30 years after the first signs show up. But it may progress faster in severe cases.

There is no satisfactory cure to stop or prevent Huntington’s chorea, but some treatments help control the symptoms. Tranquilizers and antipsychotic drugs help in controlling the involuntary movements, any violent outbursts, and possible hallucinations, but these medications may also result in side effects like additional stiffness and rigidity or sedation. Speech and physical therapy may help control the problems of impaired speech and keep muscles flexible and strong, respectively. Occupational therapy may help the suffering person cope with concentration and memory problems.

There is continuous research going on to find a treatment to slow the progress of Huntington’s disease. According to an article on CNN.com, the combination of certain cancer and AIDS drugs has resulted in the halting of Huntington’s disease in a model system of fruit flies. However, these drugs have not been tested on humans yet and it may be a while before a conclusive therapy for this disease is devised.