SEATTLE - Sitting in a small evaluation room at the University of Washington, apprehension written on her face, Christa Zamora turned her eyes toward her son Connor and contemplated his future. A talkative and animated 2-year-old, Connor appears normal, Ms. Zamora said, but it is too soon to be certain. Doctors diagnosed autism in her older son, Cameron, just before he turned 3. And with Connor, who is also at risk for developing the devastating neurological disorder, which runs in families, she has decided to be proactive, enrolling him in an early diagnosis study for children as young as 16...