The proposed connection between premature birth and autism may be more complicated than it seems, according to a new report. Early birth may not cause classically defined autism but, rather, may predispose children to autism-like symptoms that are part of a larger syndrome, the researchers say.

Deletions or duplications of chromosomal segment 16p11.2 — previously reported as a key autism region — are seen in people with developmental delays and speech and behavioral problems, but not necessarily autism. That’s the finding from two large studies published last week of people carrying these rare genetic variations.

Although the head overall is bigger in some children with autism, researchers have found more informative differences in size — some smaller, some larger — across regions of the brain.