James Doohan, the actor who played the engineer Scotty on the original 1960s “Star Trek” TV series, has been diagnosed with Alzheimer’s disease, his agent says. Doohan, 84, is in the beginning stages of the progressive neurological disorder, said the agent, Steven Stevens. Doohan, who lives in the Seattle suburb of Redmond, also has suffered for some time with Parkinson’s disease, diabetes and fibrosis, the latter due to chemical exposure during World War II, when he was a soldier in the Canadian military, Stevens said. One of Doohan’s sons, Chris Doohan, 45, said, “His longterm memory seems to be intact. If you ask him how he got his role on ‘Star Trek’ or about D-Day, he can talk for an hour about that. But if you ask him what he had for breakfast ? .” Doohan’s career spans more than 50 years, but he’s best known for his role as the USS Enterprise’s affable chief engineer.