A national search turned up about 12,000 cases.
The numbers reported Thursday translate to 4 cases per 100,000 Americans — similar to estimates from Europe and some small U.S. studies.
The Centers for Disease Control and Prevention report notes it's most common in older white males,
The disease is also known as amyotrophic lateral sclerosis, or ALS. It attacks nerve cells and often starts with muscle twitching and weakness. Roughly three-quarters of people with the disease die within five years. It's most famous victim was Gehrig, the baseball star who died from it in 1941.
CDC report: http://www.cdc.gov/mmwr/mmwr_ss/ss_cvol.html