Evaluation of the GABAergic nervous system in autistic brain: (123)I-iomazenil SPECT study

Purpose

To evaluate the GABA_A receptor in the autistic brain, we performed ¹²³I-IMZ SPECT in patients with ASD. We compared ¹²³I-IMZ SPECT abnormalities in patients who showed intellectual disturbance or focal epileptic discharge on EEG to those in patients without such findings.

Subjects and methods

The subjects consisted of 24 patients with ASD (mean age, 7.3 ± 3.5 years), including 9 with autistic disorder (mean age, 7.0 ± 3.7 years) and 15 with Asperger’s disorder (mean age, 7.5 ± 3.2 years). We used 10 non-symptomatic partial epilepsy patients (mean age, 7.8 ± 3.6 years) without intellectual delay as a control group.For an objective evaluation of the ¹²³I-IMZ SPECT results, we performed an SEE (Stereotactic Extraction Estimation) analysis to describe the decrease in accumulation in each brain lobule numerically.

Results

In the comparison of the ASD group and the control group, there was a dramatic decrease in the accumulation of ¹²³I-IMZ in the superior and medial frontal cortex. In the group with intellectual impairment and focal epileptic discharge on EEG, the decrease in accumulation in the superior and medial frontal cortex was greater than that in the group without these findings.

Conclusion

The present results suggest that disturbance of the GABAergic nervous system may contribute to the pathophysiology and aggravation of ASD, since the accumulation of ¹²³I-IMZ was decreased in the superior and medial frontal cortex, which is considered to be associated with inference of the thoughts, feelings, and intentions of others (Theory of Mind).