Huntington's Disease - Symptoms, Causes and Treatments
Huntington's disease (HD) is a genetic disorder that causes neurons (nerve cells) in particular parts of the brain (basal ganglia) to degenerate, resulting in debilitating physical, cognitive and emotional problems.
People with HD have a shortened life expectancy, dying of complications.This disorder was previously known as "Huntington's Chorea".
The symptoms of HD usually appear in middle age (mid-30s to mid-40s) and worsen over time. Less commonly, symptoms may appear before 35 or after age 45.
In some families the onset can occur in childhood and this is referred to as juvenile HD. Generally, the earlier the symptoms appear, the faster the disease progresses.
HD is caused by a mutation in a single gene (IT15). The mutation in HD is known as a CAG triplet repeat and a diagnosis is confirmed when a person has more than 40 repeats. Normal genes have less than 26 repeats. Repeat sizes between 26 and 40 need careful interpretation as they may or may not be associated with symptoms for the individual and his/her offspring.
Each child of a person (male or female) with the HD gene has a 50% chance of inheriting it. If they do receive the gene, they will develop HD at some stage,as well as risk passing the disease on to their own children. Someone who does not inherit the altered gene is not at risk, and neither are his or her children.
In some cases, HD occurs with no family history of the disease.
When the faulty gene becomes active, certain types of brain cells start to die, resulting in HD symptoms. Damage is visible in the cells’ dendrites (the branched extensions that conduct impulses from other cells).
It is not known exactly how HD causes the death of neurons, but it probably interferes with the way cells’ life spans are genetically programmed. Understanding exactly how the mutated gene affects cell death is the focus of ongoing research.
Symptoms are physical, cognitive and psychological.These do not appear in any specific order and vary in type and intensity from person to person.
However, in all cases HD is progressive – it gets worse with time. It becomes harder for affected people to look after themselves and they may ultimately become bedridden or need to be institutionalised.
The most characteristic, visible sign of HD is chorea: involuntary movements of the limbs that affect walking in particular. (In a few cases, chorea does not occur.)
Chorea starts mildly: fidgeting, restlessness or twitching of the fingers, toes, face or limbs; some loss of co-ordination and balance; clumsiness; slight changes in handwriting, and minor difficulty with skills like driving. These signs may get worse when the person is anxious.
As the disease progresses, chorea intensifies, causing jerks of the head, neck, arms and legs. Walking may become difficult as co-ordination deteriorates, resulting in stumbling, bumping into objects and falling. Speech may be slurred. Swallowing, eating and speaking are affected by the loss of muscle co-ordination. Some people may develop rigid muscles, move very little, or stop moving completely.
In the early stages of HD,it may not seem that cognitive brain functions –thinking, judgement, planning and memory –are affected; but gradually, subtle changes appear.
Short-term memory may be reduced. Tasks requiring concentration, planning and judgement may become harder. Affected people may struggle to perform routine tasks, cope with new situations, learn new information, answer questions or make decisions. Intellectual tasks become increasingly difficult.
Some HD patients lose the ability to recognise facial expressions, or even to recognise family members. Most, however, remain aware of and engaged with their environment.
Changes to personality also begin subtly and vary greatly. In the early stages, a person may simply appear unusually irritable or moody. This will intensify. Depression is common.
Other emotional symptoms include impulsivity, poor judgement, apathy or blunted emotions, anger, anxiety, egocentrism, aggressive or compulsive behaviour and hypersexuality. Some patients may laugh, smile or cry at inappropriate times.
Juvenile HD symptoms:
A very small percentage of people develop the disease before age 20, or as children or even infants. These juvenile Huntington’s patients are more likely to experience rigidity and bradykinesia (very slow movement) rather than chorea.
Early signs are frequently a rapid decline in schoolwork, small changes in handwriting and slight movement problems: tremor, twitches, slowness or rigidity. Seizures and mental disabilities may develop. Juvenile-onset HD progresses rapidly and is usually fatal in about 10 years.
In adult HD, death usually occurs 10 to 30 years after diagnosis, most often due to heart failure or infection (especially pneumonia). There is a high risk of choking and respiratory complications, due to problems swallowing: food can block the airways or enter the lungs, causing infection. Fatal falls and gastrointestinal diseases are also common.
The hardships of the disease lead to considerable stress, which can suppress the immune system. There is an elevated suicide rate in people with HD, due to stress and anxiety, as well as to psychiatric impairment.
If you know that you are at risk for developing HD, you may become hyper-alert for possible symptoms. It is important to be aware that many of the early symptoms (clumsiness, forgetfulness) are often also experienced by people without HD.
The gene responsible for HD was identified in 1993, allowing the development of a genetic test for the disease. The test involves DNA analysis to identify the CAG repeat sizes.
Prenatal testing is also available, if parents are concerned about the HD status of an unborn child.
Pre-implantation genetic diagnosis (PGD) is also available. This technique involves testing one cell of an embryo for the HD mutation. Only embryos with normal repeat sizes are transferred to the uterus. Because PGD involves testing an embryo, a couple needs to undergo IVF. PGD is available in South Africa.
To make a diagnosis, a doctor will also take a full medical and family history and do a clinical examination, involving physical and neurological evaluation.
Brain imaging – MRI, CT or PET scans – can show characteristic changes in the brain. Generally, these scans are used in patients who lack the HD gene, to identify other disorders with similar symptoms.
Those who are at risk but do not yet have symptoms may choose to be genetically tested. Because there is no cure, and because such tests cannot predict the onset or severity of the disease, this decision should be carefully considered.
Psychological and genetic counselling for the patient and relatives is essential for this purpose. The predictive testing programme assists the individual to make the decision of whether he/she wants to know this information before the onset of symptoms. It also supports the person through the testing process.
Pre-symptomatic testing is not advised for children younger than 18 years of age.
If the person does have HD, they and their family need to make important decisions about the future. With the guidance of a counsellor or therapist, various issues should be discussed, for example: legal implications, options for nursing care or institutionalisation, and end-of-life concerns. A positive test result will also affect a person’s decision to have children.
There is unfortunately no cure for HD yet, and no treatment to slow its progression. Researchers continue to study the HD gene, and are exploring possibilities for future treatments, for example in the field of stem-cell research.
There are treatments that can help relieve certain symptoms, and support services can ease the burden of the disease.
People with HD can improve their quality of life by aiming to remain physically, mentally and socially active for as long as possible.
A doctor can prescribe medication to help manage or improve certain symptoms:
- Antipsychotics may help to suppress chorea and control psychiatric problems such as agitation, violent outbursts, hallucinations or psychosis.
- Anti-seizure and anti-anxiety drugs may help to alleviate chorea, dystonia and muscle rigidity.
- Drugs such as reserpine and tetrabenazine deplete monoamine (a brain chemical), also reducing chorea.
- Antidepressants may help counter depression, anxiety and obsessive-compulsive behaviours.
- Mood-stabilising drugs (e.g. lithium)can be helpful.
- Antiparkinsonian medication can sometimes help in juvenile cases, for tremors. However, this is generally ineffective in adults.
Note: many of these drugs have serious side-effects; these should only be used in severe cases. The medication regime will probably change over the course of the disease, and should be regularly assessed by a doctor.
Proper diet and eating habits are extremely important for people with HD.
- Most HD sufferers need a large amount of calories to maintain body weight.
- They also require a lot of fluid, especially in hot weather. In some cases, water must be thickened with additives to aid swallowing.
- Eating should not be rushed. Some foods must be thickened, thinned, cut small, softened or pureed for easy swallowing.
- Dairy products increase mucus and the risk of choking.
- People who struggle with the swallowing action can be helped with “swallowing therapy”.
- Special plates, utensils and straws reduce spilling and make eating and drinking easier.
- Ask a doctor for guidance on dealing with incontinence, constipation or other gastrointestinal problems.
Exercise improves a person’s physical and mental state. For people with HD, exercise tends to improve symptoms and slow the disease.
- People with HD should walk as much as they can, with assistance if required. Strong, easy-to-put-on shoes are helpful. Avoid environments with obstacles that may be hurtful in a fall. You may wish to wear protective padding, or small ankle weights to improve stability.
- A physical therapist can teach exercises that improve strength, flexibility, balance, mobility, posture and co-ordination, and that reduce pain and help prevent falls. Therapy techniques may also include massage, stretching, traction and electrostimulation.
- An occupational therapist can advise on the use of handrails, assistive devices for tasks like bathing and dressing, and special tableware.
- A psychiatrist, psychotherapist or social worker can help someone with HD to develop coping strategies, manage behavioural and mood problems, and communicate with family.
- A speech therapist can help a person communicate (whether talking or by some other method) and can address difficulties with eating and swallowing.
Source: Australian Huntington’s Disease Association