Kennedy's disease is caused by a trinucleotide repeat expansion in the androgen receptor gene

DNA or RNA

(and for smaller polymers; di and trinucleotide)

It is possible to test someone who is at risk for developing DM1 before they are showing symptoms to see whether they inherited an expanded trinucleotide repeat. This is called predictive testing.

The phenomenon of an expanding trinucleotide repeat in successive generations is called anticipation. Another unique aspect of fragile X syndrome is that mosaicism is present in 15-20% those affected by the condition

Usually some form of damage to the cerebellum, for example a stroke that causes the death of some of the cerebellum.