We investigated brain chemistry of the primary region of the brain involved in auditory processing in adults with autism spectrum disorder (ASD). Due to the highly heritable nature of ASD and the lack of prior brain chemistry data on unaffected first-degree relatives, we also enrolled parents of children with ASD (pASD), comparing both groups to a healthy adult control group. The technique used to quantify chemical signals was magnetic resonance spectroscopy (MRS), which we used to assess the concentration of auditory glutamate, the primary excitatory brain neurotransmitter, as well as other metabolites that assess neuronal integrity and metabolism. We found significantly higher levels of auditory glutamate in persons with ASD. In addition, increases in two other metabolites, n-acetyl-aspartate (NAA), and creatine (Cr), were observed in the ASD group. No differences were observed in the pASD group in any MRS measurement. We interpret the glutamate finding as suggestive of an increase in brain excitability, and the NAA and Cr findings as indicative of a change in brain energy metabolism in ASD.
Increased glutamate levels have been reported in the hippocampal and frontal regions of persons with autism using proton magnetic resonance spectroscopy (1H-MRS). Although autism spectrum disorders (ASD) are highly heritable, MRS studies have not included relatives of persons with ASD. We therefore conducted a study to determine if glutamate levels are elevated in people with autism and parents of children with autism.
Single-voxel, point resolved spectroscopy (PRESS) data were acquired at 3T for left and right hemisphere auditory cortical voxels in 13 adults with autism, 15 parents of children with autism, and 15 adult control subjects. The primary measure was Glx. Additional measures included n-acetyl-aspartate (NAA), choline (Cho), myoinositol (mI) and creatine (Cr).
The autism group had significantly higher Glx, NAA and Cr concentrations than the control subjects. Parents did not differ from control subjects on any measures. No significant differences in Cho or mI levels were seen among groups. No reliable correlations between autism symptom measures and MRS variables were seen after Bonferroni correction for multiple comparisons.
The elevation in Glx in autism is consistent with prior MRS data in the hippocampus and frontal lobe and may suggest increased cortical excitability. Increased NAA and Cr may indicate brain metabolism disturbances in autism. In the current study, we found no reliable evidence of a familial effect for any spectroscopy measure. This may indicate that these metabolites have no heritable component in autism, the presence of a compensatory factor in parents, or sample specific limitations such the participation of singleton families.