At What Age Does HD Appear?
The rate of disease progression and the age at onset vary from person
to person. Adult-onset HD, with its disabling, uncontrolled movements,
most often begins in middle age. There are, however, other variations
of HD distinguished not just by age at onset but by a distinct array of
symptoms. For example, some persons develop the disease as adults,
but without chorea. They may appear rigid and move very little, or not
at all, a condition called akinesia.
Some individuals develop symptoms of HD when they are very young
before age 20. The terms "early-onset" or "juvenile" HD are often used
to describe HD that appears in a young person. A common sign of HD
in a younger individual is a rapid decline in school performance. Symptoms
can also include subtle changes in handwriting and slight problems with
movement, such as slowness, rigidity, tremor, and rapid muscular twitching,
called myoclonus. Several of these symptoms are similar to those seen
in Parkinson's disease, and they differ from the chorea seen in individuals
who develop the disease as adults.
These young individuals are said to have "akinetic-rigid" HD or the Westphal
variant of HD. People with juvenile HD may also have seizures and mental
disabilities. The earlier the onset, the faster the disease seems to progress.
The disease progresses most rapidly in individuals with juvenile or early-
onset HD, and death often follows within 10 years.
Individuals with juvenile HD usually inherit the disease from their fathers.
These individuals also tend to have the largest number of CAG repeats.
The reason for this may be found in the process of sperm production. Unlike
eggs, sperm are produced in the millions. Because DNA is copied millions
of times during this process, there is an increased possibility for genetic
mistakes to occur.
To verify the link between the number of CAG repeats in the HD gene and
the age at onset of symptoms, scientists studied a boy who developed HD
symptoms at the age of two, one of the youngest and most severe cases
ever recorded. They found that he had the largest number of CAG repeats
of anyone studied so farnearly 100. The boy's case was central to the
identification of the HD gene and at the same time helped confirm that
juveniles with HD have the longest segments of CAG repeats, the only proven
correlation between repeat length and age at onset.
A few individuals develop HD after age 55. Diagnosis in these people can be
very difficult. The symptoms of HD may be masked by other health problems,
or the person may not display the severity of symptoms seen in individuals
with HD of earlier onset. These individuals may also show symptoms of
depression rather than anger or irritability, or they may retain sharp control
over their intellectual functions, such as memory, reasoning, and problem
There is also a related disorder called senile chorea. Some elderly individuals
display the symptoms of HD, especially choreic movements, but do not become
demented, have a normal gene, and lack a family history of the disorder.
Some scientists believe that a different gene mutation may account for this
small number of cases, bu this has not been proven.
Source: National Institute of Health - Information on HD. Click on topic
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