About Huntington Disease (HD)
Huntington disease (HD) is an inherited brain disorder affecting the nervous system. It causes progressive deterioration of physical and mental capabilities, leading ultimately to severe incapacitation and eventual death, usually 15-25 years after onset. Primarily, it affects adults, usually appearing between the ages of 30 and 45. Occasionally, HD symptoms appear unusually early (before age 20, the juvenile form) or unusually late (after age 50.) Common symptoms of adult-onset HD are uncontrollable choreic movements, abnormal gait, slurred speech, difficult swallowing, cognitive impairment and personality changes.
Each child of an affected parent has a 50% chance of inheriting HD and
is said to be "at risk."
The symptoms of Huntington disease most frequently appear between the ages of 30 and 45. If symptoms have not appeared by 45, the probability that a person will develop HD grows less with each year of life. Symptoms rarely appear in a person who is 70 or over. It must be emphasized that there is much variation and not every person has all the difficulties mentioned here. While some individuals may have a great deal of difficulty with involuntary movements, others have very little. Similarly, some individuals may have more marked emotional or cognitive difficulties than others.
Early symptoms may appear as slight physical, cognitive or emotional changes. Physical symptoms may initially consist of "nervous" activity, fidgeting, a twitching in the extremities, or excessive restlessness. The individual may notice a certain clumsiness, alterations in handwriting, or difficulty with normal daily physical skills such as driving. These initial motor symptoms will gradually develop into more marked involuntary movements such as jerking and twitching of the head, neck, arms and legs, which may interfere with walking, speaking and swallowing. There are exceptions to this. Sometimes people with HD have a minimum of difficulty with chorea (involuntary movements). Where chorea is present, the movements usually increase during voluntary effort, stress or excitement, tend to decrease during rest, and disappear entirely during sleep for many people.
In addition to the initial physical symptoms of HD, there are often very subtle cognitive signs as well. These may involve little more than a reduced ability to organize routine matters or to cope effectively with new situations. There may be a loss of short-term memory which may occur several times each day. Work activities may become more time-consuming. Decision making and attention to details may be impaired.
Early emotional symptoms may be equally subtle. There may be more periods of depression, apathy, irritability, impulsiveness or there may be a change in personality. Rarely, a person may become delusional or paranoid.
All of these signs add to the concerns of the person living at risk of HD because on an "off day" all of us experience such things. It is quite usual for healthy people to be somewhat clumsy, or a bit fidgety when anxious or under stress, or to twitch or jerk when dropping off to sleep. At risk or presymptomatic (those with an increased risk after testing) individuals are well advised not to worry too much about the occasional stumble or forgetting a phone number, as these experiences happen to all of us and do not necessarily signify the onset of the disease.
Similarly, an at risk or presymptomatic person must not assume that
every little outburst or bout of depression is the start of HD. From time
to time, all of us are depressed, apathetic, irritable or impulsive. Anyone
who becomes concerned about changes in his/her physical, cognitive or emotional
behaviour should consult a doctor familiar with the detection and treatment
of Huntington's and related neurological disorders.
There has been relatively little meticulous research into the progressive development of the disorder in people with Huntington disease. However, one study suggests that the course of HD may not be as rapidly progressive or incapacitating as widely believed.
Dr. Ira Shoulson, Professor of Neurology, Pharmacology & Medicine, University of Rochester Medical Centre and his team have proposed adoption of a five-stage functional approach to coping with HD. Briefly, these stages are as follows:
Death usually occurs 15 to 25 years after onset of the disease. The
person dies, not from the disease itself, but from complications such as
pneumonia, heart failure or infection developing from the weakened condition
of the body.
Until recently, no test was available to tell if a person showing possible signs and symptoms of Huntington disease was indeed carrying the gene that causes HD. In addition, a variety of subtle early symptoms may also be present in other conditions. A physician, very often a neurologist, diagnoses HD by evaluating clinical signs and symptoms and obtaining a family history. It is extremely important for family members to give all relevant information to the doctor who is taking a family history, because this is a vital part of the diagnostic process. Be sure to mention any relatives who have experienced mental problems, or been diagnosed as having other neurological or psychiatric conditions, e.g. Parkinson's Disease, schizophrenia.
With our current knowledge, the physician may request confirmatory testing
to see if the gene that causes HD is present. This may occur in cases where
HD is suspected or where there is no, or an inconclusive, family history.
In hereditary diseases, such as Huntington's, earlier than average onset of symptoms usually means more severe disease. There is usually a shorter course and a greater variety of symptoms. Children with HD show a disorder of movement and posture somewhat different than the usual HD adult, a disorder of mental function, and often a convulsive disorder or tendency to epileptic seizures, something almost never seen in HD adults. The earlier the disease onset, the more likely the child is to be very rigid and very different in appearance form the majority of adult cases. Clinical symptoms differ between early onset and adult onset HD. In 1969, it was determined that children with HD, both boys and girls, were much more likely to have an affected father than an affected mother. Through research and observation, we are learning more about this rare form of HD each day.