Large brains linked to regressive autism: Study

By Dr. Ananya Mandal, MDNov 29 2011

A new study has explored the link between large brain size and autism.

Autism symptoms can appear in babies, however some children with the disorder develop normally until about age 2 when they suddenly regress. This is termed regressive autism and has been associated with larger brain size in boys.

In this new study researchers at the UC Davis MIND Institute, show there are multiple biological subtypes of autism including likely differences between males and females. They looked at 114 children with autism spectrum disorder between the ages of 2 and 4 and compared them with 66 healthy children of the same age. Of the 114 with the disorder, 54% had regressive autism and 46% had non-regressive autism.

Brain scans of the children showed that abnormal head growth and brain enlargement was identifiable in 22% of males with regressive autism compared with 5% of males with the non-regressive type. Girls with autism did not show brain enlargement. The data suggest that the abnormal brain growth occurred at around 4 to 6 months of age, much earlier than the symptoms of regression - such as a decline in speech - actually appear.

The study was published this Monday in the Proceedings of the National Academy of Sciences. Researchers David G. Amaral and Christine Wu Nordahl are particularly interested in understanding the disorder in girls. “[I]t is likely that the pattern of pathology is different in females than in males,” they wrote.

Amaral said the findings shed light on the complexity of autism and its many subgroups, which he and his colleagues are trying to understand through a long-term study of autistic children. “There’s enormous heterogeneity in the disorder, and there’s a lot of kids with characteristics that overlap with kids who develop normally,” Amaral said. “This study confirms the idea that big brains are one scenario of autism, but it’s not the only scenario.”

Autism is four times more likely to occur in boys than in girls, according to the U.S. Centers for Disease Control and Prevention, but scientists know very little about the neurological underpinnings of this gender difference. “It’s important to remember that not all kids with autism have the same form of brain pathology,” Nordahl said. “We need to keep looking for these different subgroups of autism so we can better target our treatments for the disorder.”