Slightly off-topic, but there is an interesting connection between Chorea Huntington and the evolution of complex brains and intelligence:
https://www.economist.com/news/science-and-technology/216457...
https://www.economist.com/news/science-and-technology/216457...
Something that may be related... The same unstable repeat that causes the disease is ancient and is conserved throughout mammals! So other mammals can get a similar disease driven by the same mutations. This is useful for generating models of the disease in other mammals (e.g. mice). Such conservation of repeats is exceptionally rare.