In 1990, a topical storyline was aired in which Mo was given Alzheimer's disease. During the year, Mo was shown to grow increasingly more forgetful, and after tests, Frank was informed that Mo was suffering with dementia. The storyline was scripted to show the effects on a family when a parent/loved one suffers from Alzheimer's. By November that year, Mo was in advanced stages of mental deterioration. It was at this stage that the character was written out of "EastEnders", Edna Doré having decided to end her contract. On-screen, Mo was sent to live with her daughter in Colchester, having convinced herself that Frank wanted to kill her. Writer Colin Brake has suggested that the storyline had to be curtailed earlier than they would have liked due to Doré's desire to leave.