Adults with autism have regional differences in brain volume in areas that play a role in social behavior and communication compared with controls, according to a large study published in the February issue of Archives of General Psychiatry. The differences correlate with the severity of autism symptoms, the study also shows.

Dysregulation of the intracellular signaling pathway RAS, a risk factor for idiopathic autism, may provide a unifying theory of the disorder. Although this is not an altogether new hypothesis, several new findings have strengthened the evidence for it considerably.

Larger brains may be associated with regressive autism, but only in boys, according to a study published online 28 November in the Proceedings of the National Academy of Sciences.

Toddlers with autism who have larger-than-normal heads are also taller and weigh more than controls, according to a study published in October in Archives of General Psychiatry.

Children with autism have an abnormally large number of neurons in the prefrontal cortex, a brain region important for abstract thinking, planning and social behaviors, according to a study published yesterday in the Journal of the American Medical Association.

Girls with autism have more brain matter than do either controls or girls with developmental disabilities. This defect is particularly pronounced in the left superior frontal gyrus, a region in the medial prefrontal cortex that is responsible for higher-order cognitive function.

Individuals who have autism and dysmorphology comprise a distinct subgroup within the disorder, says geneticist Judith Miles. 

Charcot-Marie-Tooth disease and autism are both associated with alterations in the number of copies of certain genetic regions, mutations in multiple candidate genes and with both inherited and spontaneous mutations, notes human geneticist James Lupski.

Individuals with a duplication of a chromosomal region associated with autism and intellectual disability are at higher risk for low birth weight, restricted eating leading to extreme thinness, and smaller-than-average head size.

The rapid brain growth seen in children with autism occurs early in life, before children reach 2 years of age, according to a study published in the May issue of Archives of General Psychiatry.