Perhaps you've seen them on Dateline, or Good Morning America. Gabrielle Williams and Brooke Greenberg are girls who don't seem to age at the same rate as the rest of us. Nine-year-old Williams weighs just 12 pounds and needs care like an infant does. By the time she was 16, Greenberg weighed 16 pounds, was 30 inches tall, still had baby teeth, and didn't speak. She died last year, at age 20.