Dane -- who shot to fame amid six seasons on the hit ABC drama "Grey's Anatomy," where he played Dr. Mark Sloan, affectionately known as "McSteamy" -- said his symptoms began over one year ago, when he began to experience weakness in his right hand.

Eric Dane and his doctor discussed his ALS diagnosis, symptoms and the rise in causes during an emotional 'Good Morning America' interview

An emotional Eric Dane is sharing about his ALS journey in his first TV interview since he publicly announced his diagnosis, telling ABC News’ Diane Sawyer that the disease does not represent the end of his story.