Charcot Marie Toothe Disease (CMT)
I have a quite common disease that no one has ever heard of! It's called CMT.
You can read about it here. Basically my peripheral nervous system (arms and legs, feet and hands) has poor signal conduction.
I have a relatively mild form which results mainly in poor balance and muscle weakness. Fortunately, my balance on a bicycle is unaffected and I've learned I can stay fit by cycling!