Applications of PET and SPECT in Patients with Autism Spectrum Disorder.

Autism spectrum disorder (ASD) consists of neurological development disorders that manifest before three years of age and affect social interactions, markedly restricting range of interests and activities, often associated with some degree of intellectual disability. Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are non-invasive imaging tools to investigate the function of the brain in vivo. SPECT and PET studies exploring rCBF and brain glucose metabolism in patients with ASD have been performed, providing important insights into the brain regions involved in ASD. Abnormalities in serotonergic, dopaminergic, GABAergic, cholinergic, and glutamatergic systems have been suggested to contribute to the observed distorted brain circuitry associated with ASD. However, the specificity of such abnormalities needs to be fully clarified because schizophrenia and other psychiatric diseases have been shown to present with comparable changes in neurotransmitter systems. Neuroinflammation could also play a role in the development of autism. Therefore, ASD is a complicated process involving a number of factors. It is mandatory to perform more research studies to determine the molecular cornerstone of ASD and to improve our comprehension of the clinical correlates of ASD.