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Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or
less.
In this installment I will discuss Huntington’s disease.
The symptoms of Huntington’s disease typically emerge during middle age and at first often
involve subtle changes in personality, cognition, and movement.
Eventually, the symptoms progress into substantial movement problems like chorea, which involves
uncontrolled, spasmodic movements; impaired coordination and balance; muscle rigidity;
and difficulty speaking and/or swallowing.
Cognitive and psychiatric symptoms like dementia and depression occur as well.
The disease is incurable and fatal.
These symptoms are associated with neurodegeneration, or the deterioration and death of neurons.
A group of structures called the basal ganglia are strongly affected, but other regions of
the brain experience neurodegeneration as well.
The pathology of Huntington’s disease can be traced back to a mutation in a single gene
called huntingtin.
The mutation that causes Huntington’s disease is a dominant mutation.
Thus, if one parent has the disease, their child has a 50% chance of developing it, too.
The huntingtin gene contains a DNA sequence that consists of three nucleotides (cytosine,
adenine, and guanine) in repetition---a pattern known as a trinucleotide repeat.
When the gene is mutated, an excess number of repeats can occur, and a mutated form of
huntingtin protein is created.
The higher the number of repeats, the greater the risk of disease, and all people with 40
or more repeats in the huntingtin gene will develop Huntington’s disease.
Mutated huntingtin proteins have a tendency to group together, forming clusters within
neurons that are not easily removed by brain enzymes.
It has been hypothesized these clusters may play a role in the neurodegeneration seen
in Huntington’s disease, for their accumulation in the brain is associated with increased
neurodegeneration.