Phylis Campbell was surprised when her son Gregory was diagnosed with autism just before his 16th birthday in 1991. As far as she knew, the condition didn’t run in her family. But as her son grew older, all sorts of small characteristics in her relatives began to take on a whole new significance.

For instance, Campbell recalled that, like Gregory, his father had intensely disliked clothes with bulky seams or itchy tags, and preferred soft fabrics. In fact, Gregory’s father had said he felt responsible for the odd preferences his son had inherited from him. He had severe depression, as did his mother, and died in 2003.

Campbell knows less about the quirks of biological relatives on her side of the family because she grew up in foster care. She has little contact with her biological parents and siblings. However, in the past decade she has learned that one of her biological sisters has a grandson diagnosed with autism.

When her daughter, Alisa, began having children, Campbell kept a watchful eye on them, searching for signs of autism. She became anxious at the slightest hint that they might miss a typical developmental milestone. When her granddaughter, Talia, was a toddler and started to walk without having first crawled, Campbell bought a battery-operated Minnie Mouse doll and crawled along the floor with it to encourage Talia to do the same. “I put her through the motions of crawling because I did not want that stage to be skipped,” she says.

Talia is now 15, and her brother Jeremy is 12. Neither has autism, but Campbell says she sees hints of it in both. Jeremy, for example, has grown anxious in the past year: He pulls out his eyelashes and has a bald spot on his head from nervously pulling out patches of his hair. Talia strives for perfection in school and is easily upset if her test scores or athletic performance are less than flawless. She also dislikes changes to her routine and needs coaxing to meet new people. “If she’s going into a new situation or a new sports group, she wants a family member to go with her because she hesitates to go out onto the field with kids she doesn’t know,” Campbell says.

For years, Campbell wondered if these traits were related somehow to her son’s condition, and worried that subsequent generations of her family would also be at risk. Then, in August, she heard child psychiatrist John Constantino speak at a workshop near her home in St. Louis, Missouri. Constantino talked about a project in which he and his colleagues would collect women’s keen observations of their children and grandchildren. The goal, according to the flyer, was ultimately to understand the risk of autism across generations — essentially what Campbell had spent dozens of hours worrying about. She immediately signed up.

Photography by Jennifer Silverberg

Campbell is one of five grandmothers Constantino’s team has recruited so far. Like her, the other women have at least one child with autism. They too have other children who do not have an autism diagnosis, and grandchildren through those children. Because these women have had children with autism, they are primed to see signs of it in the next generation. “They’re very invested in their grandchildren — they’re watching their grandchildren, interacting with them, and they’re good raters of their grandchildren’s behavior,” says Constantino, professor of psychiatry and pediatrics at Washington University in St. Louis. “Ignorance is no match for an army of grandmas.”

Campbell’s family is a particularly good fit for this study, because the work focuses on the unaffected sisters of men with autism — like Campbell’s daughter, Alisa. Studies suggest that the sisters of people with autism tend to have more autism traits than do people in the general population. They are also up to four times more likely than average to have a history of language delay that they later outgrow. Language difficulties often accompany autism, and may be a sign that the sisters carry genetic risk factors for the condition. Scientists are particularly interested in sisters because they may pass these risk factors on to their children.

Studies like these challenge conventional ways of thinking about autism. An autism diagnosis can sound categorical: either you have the condition or you don’t. But increasingly, there is acceptance among both scientists and the general public that autism-like characteristics — adhering strictly to routines, for example, or an obsessive interest in certain topics — exist in everyone. The more of these traits someone has, the closer she is to an autism diagnosis. Some traits might even influence whom she chooses as a partner — and determine the fate of future generations.