Saturday, May 22, 2010: 10:15 AM
Grand Ballroom E Level 5 (Philadelphia Marriott Downtown)
Several studies have demonstrated amygdala enlargement in young children with autism (Sparks 2002, Schumann 2004, Mosconi 2008, Schumann 2009). However, longitudinal data on rate of growth has not yet been extensively evaluated.
We report findings in a large sample of 2-3 year old males (n = 101; 72 ASD 29 Typical development). A subset of children in this sample received a longitudinal one year follow up scan (n = 38; 24 ASD, 14 Typical development). Rate of amygdala growth relative to total cerebral volume was examined.
All MRI scans were acquired during natural nocturnal sleep, without the use of sedation or anesthesia. A high-resolution 3D MPRAGE sequence was acquired using a 3T Siemens Trio system. Total cerebral volume and amygdala volume were manually traced using Analyze 9.0 software. For longitudinal analyses, amygdala volume was normalized to total cerebral volume and percent change was calculated, taking into account ages at baseline and follow-up MRI scans.
Cross-sectional results of the entire sample indicate a larger right amygdala (p = .04) and a trend towards a larger left amygdala (p = .07) in the ASD group after covarying for age and total cerebral volume. Longitudinal analyses revealed substantial heterogeneity within the autism group. For typically developing children, the mean percent change was 4.3%. Twelve out of 24 (50%) children with autism demonstrated a similar rate of growth (4.2% increase). However, there were two distinct subgroups within the ASD group, one with rapid growth (n = 7 (29%), 17.6% increase), and one with slow growth (n = 5 (21%), -5.6% growth [negative number signifies that TCV was growing more rapidly than amygdala]).
Children in this study are part of a larger multi-disciplinary study, the Autism Phenome Project, through which various measures, including extensive behavioral indices, immunological and genetic profiles, and auditory event related potentials are being collected in the same population of children. Efforts will be made to characterize the three different subgroups based on these other measures. Preliminary findings suggest autism severity is positively correlated with increased rate of amygdala growth.
While overall enlargement of the amygdala is present in 2-3 year old children with autism spectrum disorders, there is substantial heterogeneity in the rate of growth. Specifically, while the typical group showed considerable homogeneity in their growth pattern, more than a quarter of children with ASD showed accelerated amygdala growth of four times the typical rate. One in 5 showed dramatically slower than typical growth. Overall, increased rates of amygdala growth are correlated with more severe symptoms of autism. The identification and further characterization of subgroups such as these will be fundamental to understanding the heterogeneity within autism spectrum disorders.