When is the brain enlarged in autism? A meta-analysis of all brain size reports

Background: Multiple studies have reported increased brain size in autism, while others have found no difference from normal. These conflicting results may be due to a lack of accounting for age-related changes in brain enlargements, use of small of small sample sizes, or differences in data acquisition methods. Methods: Reports of autism head circumference (HC), magnetic resonance imaging (MRI), and post-mortem brain weight (BW) that met specific criteria were identified and analyzed, Percent difference from normal values (%Diff) and standardized mean differences (SMD) were calculated to compare brain size across studies and measurement methods. Curve fitting, analysis of variance and heterogeneity analyses were applied to assay the effects the age and measurement hype on, reported brain size in autism, Results: A fitted curve of HC and MRI %Diff values from 15 studies revealed a largely consistent of brain size changes. Specifically, brain size in autism was slightly reduced at birth, dramatically increased within the first year of life, but when plateaued so that by adulthood the majority of cases within norma range. Analysis of variance of MRI and post-mortem %Diff values by age group (young child, older child, adult) and measurement .