This disease sounds like another motor neuron disease called amyotrophic lateral sclerosis (AlS). I have a cousin who has this. It's also caused by a degeneration of neurons and has the same symptoms like muscle atrophy and weakness.
I think the main difference between Kennedy's disease and ALS is that ALS is not as rare as Kennedy's. I'm sure the gene that carries them is different too although I don't know specifically.
Anyone know what other differences there are between these nervous system diseases?