Brother of actor Sean Astin. Son of Patty Duke and John Astin. Was accepted to Johns Hopkins University, but did not enroll. Brother-in-law of producer Christine Astin. Uncle of actress Alexandra Astin and Elizabeth Louise Astin. Dominic Monaghan was his roommate for a while. Mackenzie later made a guest appearance on Dominic's TV show, "Lost" (2005). Nephew of Ray Duke. Has three other half brothers: David, Allen and Tom
