Allison Chang has known for about a decade that her eldest son has autism and ADHD. She is part of a provincial research network investigating the biological underpinnings of neurodevelopmental disorders. And for the past year, she has been actively researching her son’s co-occuring diagnoses, pursuing a social work PhD at the University of Toronto. Ms. Chang, 53, understands the complexities of autism spectrum disorder and its underlying causes, which scientists believe to be an intricate interplay between genetics and environmental influences. But last September, she found herself...