U.S. researchers report in the new issue of the Proceedings of the National Academy of Sciences (PNAS) that some boys with degenerative autism have abnormal brain growth at 4 months of age, with brain volumes about 6 percent larger than those of their healthy peers. Researchers at the University of California, Davis, analyzed head circumference and brain growth data from 180 children between the ages of 2 and 4 years. Sixty-one of these children had degenerative autism, 53 had early-onset autism and the rest were healthy children. The researchers found that the boys with degenerative autism began to experience abnormal brain growth as early as 4 months of age, a condition that can persist for up to 19 months. Healthy boys, boys with early-onset autism and girls showed normal brain growth. This study provides further evidence that there are subtypes of autism with different neurobiological underpinnings and that there is a specific association between abnormal brain growth and boys with degenerative autism. Rapid brain growth in boys may be a criterion for the diagnosis of degenerative autism. Autism, also known as autism, is a severe mental developmental disorder. Individuals with autism typically develop before the age of 3 years and are characterized primarily by indifference to emotion, refusal to communicate, delayed language development, repetitive stereotyped behavior, and a markedly limited range of activities and interests.