The footage of the young girl with progeria was filmed after the production crew contacted the Progeria Society and were put in touch with the family of Courtney Arciaga, who was a young girl with the disease. She and her family were fans of the series, and were flown from their San Diego home to Vancouver to shoot the scene.
The CIA man in the background of the final scene is William B. Davis (Cigarette Smoking Man) making his second appearance on the show. Like his first there appears to be no dialogue.
Robin Mossley, who appears as Dr. Joe Ridley, would go on to appear in further episodes of The X-Files, playing Dr. Vance Randolph in Our Town (1995) (season 2) and Dr. Kingsley Looker in Terma (1996) (season 4).