symptoms can appear in babies, however some children with the disorder develop normally until about age 2 when they suddenly regress. A new study has linked this second type of autism -- regressive autism -- with larger brain size in boys.
Other studies have suggested some association between overgrowth of the brain and autism. The new study, led by researchers at the UC Davis MIND Institute, demonstrates that there are multiple biological subtypes of autism including likely differences between males and females.
Researchers 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, published Monday in the
, adds to a growing body of evidence showing autism likely has various biological underpinnings. Researchers 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.