Dr. Jean-Martin Charcot, a French neurologist, first described ALS in 1869. He was the first physician to link symptoms of ALS to a group of nerves specifically affected by the disease - the motor neurons that originate in the spinal cord.
It is difficult to diagnose ALS because it resembles other diseases, such as primary lateral sclerosis, progressive bulbar palsy, progressive muscular atrophy, and progressive pseudo bulbar palsy. There appear to be two main types of ALS in the general population: [Familial] Approximately 5-10 percent of ALS cases are familial. Of those cases, 20 percent have a genetic defect in a specific chromosome; [Sporadic] About 90 percent of cases have no definitive cause.