What goes wrong in lou gehrig's disease?

Nerve cell death: Nerve celles that produce movement begin to die causing weakness that affects the arms and legs and eventually the muscles that control swallow and speech.

NOT fully clear: We do know it is a disease which results in loss of motor nerve cells in brain and spinal cord, and there is an incidence of 10% familial involvement. Rarely, there is a mutation in gene encoding of copper/zinc superoxide dismutase, but otherwise, we are not clear as to what is causing this devastating condition.