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| printer friendly | HUNTINGTON'S DISEASE | ||||||||||||||||||||
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Huntington's disease: Huntington's Chorea Huntington's disease (HD) is a neurodegenerative disorder, characteristically affecting the basal ganglia but also affecting other areas of the central nervous system. Onset is usually in the fourth or fifth decade, but HD can occur more rarely in childhood or extreme old age. The clinical features of HD can be thought of as a triad of emotional, cognitive and motor disturbances. Early in the disease, manifestations can include subtle changes in co-ordination, minor involuntary movements, difficulty thinking through problems, and often, a depressive and irritable mood. In the middle stage, the involuntary movement disorder, known as chorea may become prominent, and difficulty with voluntary motor activities will be more evident. Speech becomes more difficult to understand, and there can be difficulties in swallowing safely. As cognitive and movement problems increase, the patient will be unable to work. Patients in the late stage may have chorea but quite often have slow voluntary movements. They may become unable to speak and bedridden and will require total care. The cognitive impairment is selective so, despite their difficulties with speech, patients may still be able to understand conversations, although their ability to make decisions will be very impaired. The duration of the disease is variable with an average of fifteen years frequently quoted. There is no cure for HD at present, though much research is underway. None the less it is possible to find out whether one has the responsible mutation (or genetic change) which causes the disease. This predicts with great accuracy whether someone will develop the disease or not. The knowledge that one has the gene for HD can create significant difficulties with insurance, employment and relationships, even before the disease manifests itself, and it is important to seek expert advice from a clinical genetics centre about such tests. Juvenile Huntington's disease The age of onset of HD is very variable: in around five per cent of cases onset can be under the age of twenty years and in very rare cases the onset can be under the age of ten years. Given that juvenile HD (JHD) is defined by the age of onset, it follows that at any one time a number of people who started with HD under the age of twenty years will now be over twenty years old. In general, young people with JHD are likely to present with difficulties at school and perhaps some clumsiness. The earliest features of JHD are not very specific so parents may experience a delay between being concerned about a young person and a genetic test being performed; this may lead to frustration. A genetic test can answer the question as to whether or not the gene for HD is present but the decision about whether or not the condition has started remains a matter of judgement. As the early features of JHD are often non-specific, doctors may wait for clearer neurological signs before doing the test. The neurological features of JHD differ from that seen with the more classical onset. Slowness of movement, called bradykinesia, rather than chorea is likely to occur; as the disease progresses, there may be slurred speech, dystonic movements (which result in the limbs adopting unusual postures) and muscle cramps. Epilepsy is more likely to occur in JHD than in the more usual form. As with the adult form of HD the intellectual problems are selective which may manifest itself as behavioural problems. Inheritance patterns Prenatal diagnosis Where the parent does not want a predictive test for himself/herself exclusion testing on the fetus may be possible. This will either give the fetus a low risk status or the same risk status as the parent. Further details can be obtained from regional genetic centres Medical text written November 1996 by Dr S Simpson. Last updated September 2005 by Dr S Simpson, Associate Specialist/ Senior Lecturer in Clinical Genetics Clinical Genetics, Grampian University Hospitals, Aberdeen, UK. Additional material on Juvenile Huntington's disease written July 2005 by Dr D O Quarrell, Consultant in Clinical Genetics, Centre for Human Genetics, Sheffield, UK. Further Online Resources
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