Objective: An imbalance of excitatory and inhibitory neurotransmission in autism spectrum disorder (ASD) has been proposed. We compared glutamate (Glu), glutamine (Gln), and γ-aminobutyric acid (GABA) levels in the anterior cingulate cortex (ACC) of 13 males with ASD and 14 typically developing (TD) males (ages 13-17), and correlated these levels with intelligence quotient (IQ) and measures of social cognition.
Methods: Social cognition was evaluated by administration of the Social Responsiveness Scale (SRS) and the Reading the Mind in the Eyes Test (RMET). We acquired proton magnetic resonance spectroscopy ((1)H-MRS) data from the bilateral ACC using the single voxel point resolved spectroscopy sequence (PRESS) to quantify Glu and Gln, and Mescher-Garwood point-resolved spectroscopy sequence (MEGA-PRESS) to quantify GABA levels referenced to creatine (Cr).
Results: There were higher Gln levels (p=0.04), and lower GABA/Cre levels (p=0.09) in the ASD group than in the TD group. There was no difference in Glu levels between groups. Gln was negatively correlated with RMET score (rho=-0.62, p=0.001) and IQ (rho=-0.56, p=0.003), and positively correlated with SRS scores (rho=0.53, p=0.007). GABA/Cre levels were positively correlated with RMET score (rho=0.34, p=0.09) and IQ (rho=0.36, p=0.07), and negatively correlated with SRS score (rho=-0.34, p=0.09).
Conclusions: These data suggest an imbalance between glutamatergic neurotransmission and GABA-ergic neurotransmission in ASD. Higher Gln levels and lower GABA/Cre levels were associated with lower IQ and greater impairments in social cognition across groups.