When Erin Lopes’ son Tommy was 15 months old, she became alarmed when he stopped saying “yes” and “no” and holding her gaze. It wouldn’t be until he was three years old that Tommy was finally diagnosed with autism.
Tommy had two first cousins on the autism spectrum, so Lopes suspected it ran in families. So she was relieved when her daughter Evee Bak, who was born 17 months after Tommy, was talking in full sentences by her second birthday. The toddler appeared to not be on the autism spectrum—what autism advocates today call “neurotypical.”
Erin’s children exemplify a question that’s mystified scientists for decades: Given that autism, a developmental disorder that impairs a person’s ability to communicate and interact, is inherited in most cases, why do girls get it at much lower rates than boys? According to a 2011 study by an international team of psychiatrists and pediatricians, nearly one-fourth of brothers of autistic children were likely to be on the spectrum, but that rate dropped to 9 percent for sisters.
Scientists have historically focused on studying a “quartet” of two biological parents and two autistic children. Yet more recent research calls for learning more about the unaffected siblings – particularly girls. And in an era where researchers can map the human genome en masse—and have identified 100 genetic regions believed to be linked to autism—there is a need for lots of DNA data from autistic and neurotypical siblings alike.