Huntington's disease

Written by Dr Linda Appai-Kubi, King's College Hospital and Guy's King's ST. Thomas's School of Medicine, London and Dr K Ray Chaudhuri, King's College Hospital and Guy's King's ST. Thomas's School of Medicine, London

What is Huntington's disease?

Huntington's disease (HD) was described by George Huntington (1850-1916) who was born in Long Island, New York. He described this disorder in his only known written article called 'on chorea'.

Huntington's disease is a genetic disorder (inherited due to a faulty gene) which usually affects people in their 40s and 50s. It primarily affects the brain, with a gradual loss of control of movement, memory and mental ability.

HD is also associated with personality changes and depression as well as other mental illnesses. There is currently no cure for HD, although many strategies may be used to improve the quality of life for sufferers and their carers.

Who gets HD?

As HD is an inherited condition it generally occurs in people with a family history of the disease. Occasionally there may be no family history and this may be due to either the disease not being diagnosed in family members of previous generations or the disease masquerading as mental illness with 'fidgetiness'.

About 8 in every 100,000 people in the UK have HD – approximately 4800 people. The highest prevalence of this disorder in the world is near Lake Maracaibo in Venezuela where it affects around 700 per 100,000 of the population.

HD is inherited in a pattern known as 'autosomal dominant'. The autosomes are all of those chromosomes within the cells of the body other than the sex chromosomes.

The chromosomes are where our body's genetic information, in the form of DNA, is stored, so this means that HD affects men and women equally and may be inherited from either a mother or a father with the condition.

The chance of an affected parent passing the disease on to their child is 50 per cent, ie if one parent is affected there is a 50-50 chance that their child will also have the disease. Each child will have the same chance of inheriting HD. People with HD often have children before developing symptoms of the disease.

A family history of HD is often the only clue to the possibility of developing the disease. Symptoms of the disease start to appear in middle age, although very young and very old people have shown signs of the disease in rare cases.

Some reports suggest a link between developing HD at a very young age (under 20 years) and inheriting the disease from the father, rather than the mother. An affected mother or father has an equal chance of passing on the older-onset form of the disease.

How is HD inherited?

Each child normally receives genetic information from both parents, in the form of chromosomes - 23 from the mother and 23 from the father.

Every cell within the human body contains this full set of genetic information. Chemicals known as 'bases' are arranged along chromosomes and form a code. This code is decoded within the cell to make proteins.

There are four bases - cytosine, adenine, guanine and thymine, usually shortened to C, A, G and T. The way in which these link together is the fundamental structure of DNA.

These proteins influence the cell in many ways, including how the cell works, and how long individual cells will live.

The genetic abnormality in HD is found on the fourth chromosome (4p16.3), and three bases arranged along a particular stretch of this chromosome occur in a repeated sequence known as a CAG repeat. The gene is called IT15, or 'huntingtin'.

Research into HD has found that an excess number of these repeats leads to the disease. Typically more than 35 repetitions of the CAG sequence is associated with HD although people with up to 39 repeats might not have the disease. This knowledge also allows people who suspect they may have HD to be tested for the disease - the test is positive if they are found to have too many repeats.

What are the symptoms of HD?

HD affects a wide range of brain activities and symptoms gradually become apparent in middle age.

Changes in personality or mood may be the earliest signs of the disease, followed by problems with memory and abnormal uncontrollable movements.

Personality change may occur as much as 10 years before abnormal movements are noticed. Most symptoms become progressively worse, although some people have fewer involuntary movements later in the course of the disease. Death usually occurs 15 to 20 years after the first symptoms, as a result of a general decline in health, or of more specific causes such as difficulty swallowing which leads to choking on food.

Movement disorders The abnormal movements, which gave HD its former name of Huntington's chorea (chorea is a Greek word meaning dance), are typically rapid, jerking movements over which the person has no control. These movements can involve all four limbs and the trunk and specific movements of the face and head can also occur.

Other abnormal movements that may develop throughout the course of the disease include slower, writhing movements of the arms and legs (known as athetosis), strange postures due to muscle spasm (dystonia) and slowing of voluntary movements in a manner similar to Parkinson's disease.

Sudden jerking movements of the limbs or trunk, known as myoclonus may occur. HD Patients may also find themselves more unstable and prone to falls when standing. Chorea may involve speech function and walking which has a peculiar 'lurching' appearance. This can lead to unsteadiness and falls.

Eye movement

Rapid movements of the eyes are also affected, particularly on looking up and down.

People with Huntington's disease can have difficulty in looking sideways too and may have to move their head to achieve full lateral vision. This is known as oculomotor apraxia.

Parkinsonism

'Parkinsonism' means the features of Parkinson's disease but due to other conditions. Many patients develop signs suggestive of parkinsonism with slowness of movement and increased muscle tone (rigidity). This usually occurs later in the disease.

In juvenile-onset HD, and rarely in older patients, the condition may present with parkinsonism rather than chorea.

Memory and other neurological symptoms

Affected persons experience forgetfulness, which gradually worsens throughout the illness. They may also find difficulty with concentration, planning, and carrying out tasks that involve sequences of events.

Thinking and thought processes appear to be slower in general but the ability to talk and understand language is preserved even in the later stages of the illness. People may also experience sensory symptoms such as numbness or pain.

Go To Next Page>>



The documents contained in this web site are presented for information purposes only. The material is in no way intended to replace professional medical care or attention by a qualified practitioner. The materials in this web site cannot and should not be used as a basis for diagnosis or choice of treatment. Conditions for use



© Copyright 1998 - 2004 NetDoctor.co.uk - All rights reserved