A dear family member just started getting symptomatic with a progressive condition where their body generates new motor control neurons (or nerves? I'm not clea

A dear family member just started getting symptomatic with a progressive condition where their body generates new motor control neurons (or nerves? I'm not clear), which aren't connected to the brain. It basically amounts to line noise on the motor control circuit, producing incredibly irritating but otherwise harmless uncontrollable motion of specific downstream body parts.