Huntington's chorea is an autosomal dominant condition due to CAG repeats.
It is carried on chromosome 4.
Symptoms tend to start in the 40s with a progression from chorea to irritability to dementia and death.
There is no cure. The chorea may be treated with a dopamine antagonist such as tetrabenazine.
Note that Hunington's has complete penetrance so a child of a sufferer has a 50% chance of being affected. Due to anticipation if they are affected they are also likely to develop symptoms earlier.
Next up: Friedreich's ataxia...