Huntington’s Disease is a genetic autosomal disorder which effects the brain. It affects about 1 in 20,000 individuals. The symptoms of the disease do not start to occur until after or around 40 years of age. With the onset of the disease the patient starts to gradually deteriorate intellectually, this deterioration also causes involuntary movements. Scientists have only recently found the section of the gene which causes Huntington’s disease, and this is allowed them to devise pre-symptomatic tests. However, a cure for the disease is yet to be found.
The symptoms of the Huntington’s disease vary from person to person. They can be grouped in two categories: Abnormal involuntary movements and intellectual deterioration, which includes memory loss. Each symptom progresses at a different rate. Sometimes the progress of the symptoms can stop after around 10 years, or it may even lessen. However, other times if the symptoms just get worse and worse it may eventually lead to death. This is usually due to infection and the deterioration of various organs in the body. In the early stages the victims can become irritable or moody.
They will have a short temper. Things that may seem inconsequential to others may be very upsetting to the person with HD who is moody and becomes angry easily. As the disease progresses emotional symptoms and personality changes are also observed. However, this could be partly due to their self-consciousness and lack of confidence. They become aggressive and have outbursts when they find it difficult to do something. A person with HD cannot manage more than one task at the same time. On 15 February, 1872, Dr George Huntington gave a speech and stated the three marked features of this disease.
He stated that this was not a new disease and he was the not the first to describe it, however his name has become associated with the disorder he summarised so successfully. It is said that Huntington’s disease was first introduced to Australia by a Somerset woman who arrived in Tasmania aboard the “Arab” ship in 1842. She had thirteen children; eight with her first husband and five with her second. Five of the six females and four of the seven males inherited the disease. This disease is genetically inherited and is a dominant characteristic, therefore unfortunately the offspring of a victim has 50% chance of inheriting the disease.
The DNA contains four types base: A (adenine) and T (thymine), G (guanine) and C (cytosine). These four letters make up the genetic alphabet and they spell out the commands for every single cell and organ of the body and also determine all the characteristics of the person. In 1993 it was discovered that a segment of DNA on the arm of chromosome 4 is linked to the HD gene. They found that at one end of the HD gene, the combination CAG is repeated too many times. In people without HD this CAG is repeated 5 to 35 times. In people who are affected by HD, CAG is repeated over and over again between 36 and 121 times.
The CAG combination codes for a protein called huntingtin. Why the increase number of CAG causes HD is still unknown. It is thought that too much of the HD protein makes them obtain some new, abnormal property. This is true in two other disorders caused by repeats of three letters, spinocerebeller ataxia type 1 and X-linked spinal and bulbar muscular atrophy. It may also be true in all CAG-related genetic diseases. The HD gene is present in almost every cell of the body. However, it only affects the brain. Moreover, the huntingtin protein is present in all parts of the brain but it only affects some parts.
The region of the brain most affected by HD is the striatum. The nerve cells in the striatum are especially affected. It is unclear why the HD gene affects that particular part of the brain so badly. One explanation suggests that the huntingtin protein, produced by the CAG letters, interacts with the “huntingtin associated protein 1” in the striatum part of the brain and therefore caused problems in that part of the brain. When there is more huntingtin protein the interaction is stronger. Studies have also found that the “huntingtin associated protein 1” is only found in that part of the brain.
This recent discovery of the HD gene allowed scientists to devise pre-symptomatic tests for Huntington’s Disease. It involves extracting DNA from the person’s blood sample and using a procedure known as the polymerase chain reaction (PCR). PCR can make numerous copies of a specific section in an individual’s DNA. PCR involves cycles of heating and cooling the DNA. The DNA is usually twisted into a double helix. When it is untwisted, we can see that the sides of the DNA strand holds the bases together. The bases contain the pairs A and T, C and G. We can also say that DNA exists in double strands
The sample is melted to make all the DNA single stranded so that the corresponding bases are separated from the side that is going to be tested. The DNA is cooled and primers find their target sequences producing small sections of double-stranded DNA. Primers also contain bases that would be corresponding to the target sequences we are trying to find in the individual’s DNA. In this case, when the sequences CAG needs to be found the corresponding GTC sequence makes up the primer. The sections of the DNA with that still remain single stranded are discarded.
The lengths of the double strands are then compared with size markers (bits of normal DNA). If the strands are too long it means that there are more than normal repeats of CAG. As well as the physical effects of the disease, there are also psychological and emotional problems relating to the reactions of the existence of the disease. Social and economic consequences of the illness also result. Therefore the victims of the disease also need counselling and support from others. Huntington’s disease is viewed by victim’s families as a socially unacceptable disease and shameful.
Therefore, the physician plays a important role in the management of a HD patient. Caring for the patient who is surrounded by family and the community requires heart, medial knowledge and social skills of the physician. There are many places a victim of Huntington’s Disease should go for support including: Huntington disease societies (eg. Australian Huntington’s Disease Association) http://www. kumc. edu/hospital/huntingtons/ There are few treatments available to a sufferer of Huntington’s disease because it is not yet curable. The only ones used now are to lessen the severity of the some symptoms and cannot treat the disease directly.
There are two major tranquillisers used: Phenothiazines – these are particularly useful when the patient needs sedation. They are also useful for patients whose abnormal movements are the strongest at night Butyrophenones: Haloperidol is a very useful medication in the control of movements and behavioural changes in HD. However the side effect of drowsiness and depressive moods needs to be monitored carefully. Lithium – Lithium is a drug. It is not useful in the management of abnormal movements. However, it reduces the patient’s degree of irritability.
