Amygdalar volume and behavioral development in autism.

CONTEXT The amygdala is associated with socioemotional function and has been implicated in the pathophysiology of autism. OBJECTIVE To examine the relationship between amygdalar volume at ages 3 and 4 years and severity of clinical course and outcome at 6 years of age in children with autism spectrum disorder. DESIGN Magnetic resonance images acquired at 3 and 4 years of age were used to measure total cerebral, amygdalar, and hippocampal volumes. Acquisition of social and communication skills was assessed semiannually using the Vineland Adaptive Behavior Scales. Hierarchical linear models were used to predict variability in individual linear growth trajectories as a function of IQ, total cerebral, and amygdalar or hippocampal volumes. SETTING Longitudinal study of children with autism spectrum disorder. PARTICIPANTS Forty-five children with autism spectrum disorders between 3 and 6 years of age. MAIN OUTCOME MEASURE Linear growth trajectory of age equivalence Vineland communication and social scores. RESULTS Larger right amygdalar volume was associated with more severe social and communication impairments at ages 3 and 4 years. Larger right amygdalar volume also was predictive of poorer social and communication abilities at age 6 years, even after controlling for IQ and total cerebral volume. Parallel analyses with hippocampal volumes found no relationship to social or communication development. CONCLUSIONS Larger right amygdalar volume at 3 and 4 years of age, but not left amygdalar, hippocampal, or total cerebral volume, is associated with a more severe clinical course and worse outcome at age 6 years in children with autism spectrum disorder. These results provide additional evidence that amygdalar development is implicated in the behavioral impairments found in autism.