Unit A Reproduction

FIGHTING HUNTINGTON’S DISEASE
Genetically modified mice are helping Vancouver scientists learn
more about this deadly genetic disease.
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Would you want to know right away if
you carried the gene? Would you rather
wait and see if you developed the
symptoms? Children of people with
Huntington’s disease must ask themselves
these questions. Huntington’s disease is
a disease of the nervous system that is
characterized by loss of memory,
reasoning, and judgment, as well as
involuntary jerky movements of the
limbs, head, and neck. The onset of
Huntington’s disease is usually between
30 and 50 years of age, and because
there is currently no cure, death occurs
from complications 10 to 15 years after
the onset of the disease. People with
Huntington’s disease usually die from
falls or choking.
Huntington’s disease is the result of
a mutation in the gene that codes for
huntingtin protein, a protein that is
essential for proper nerve cell functioning.
Amino acids are the building blocks
of proteins. Normally, the huntingtin
protein has many molecules of the
amino acid glutamine, usually between
10 and 35 in a row. In people with
Huntington's disease, the mutated
gene creates a protein that has over
40 glutamine molecules in a row. The
extra glutamines change the shape of
the protein, which in turn causes nerve
cell death. The death of nerve cells is the
cause of the symptoms and progression
of Huntington’s disease (Figure 1).
Scientists, such as Dr. Michael Hayden
at the Centre for Molecular Medicine
and Therapeutics in Vancouver, have
developed special mice that serve as
models to study this disease. These mice
were developed by transferring new
genes into the nuclei of fertilized mouse
embryos. The genetically modified mice
have symptoms that resemble Huntington’s
disease. As the mice mature and develop
symptoms, scientists learn about the
disease mechanisms and potential
treatments for Huntington’s disease.
There is a test to determine the base
sequence of the gene on chromosome 4,
which codes for huntingtin protein.
It is the only reliable way to determine
if an individual will develop Huntington’s
disease. Interestingly, many people who
have a parent with Huntington’s disease
do not want to get tested. It is an
individual choice.
Think of what it would be like to
wonder, every time you tripped or
dropped a glass, if you were getting the
disease. Without a cure, however, would
wondering be better than facing the
certainty of the disease?
Figure 1 Cross sections of a brain from a person
who died from Huntington’s disease (top) and
a normal brain (bottom). In the Huntington’s
brain, notice the large spaces created by the
death of cells in these areas of the brain.
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