Abstract
BackgroundThe autism and schizophrenia spectra overlap to a large degree in the social and interpersonal domains. Similarly, abnormal excitatory glutamate and inhibitory γ-aminobutyric acid (GABA) neurotransmitter concentrations have been reported for both spectra, with the interplay of these neurotransmitters important for cortical excitation to inhibition regulation. This study investigates whether these neurotransmitter abnormalities are specific to the shared symptomatology, and whether the degree of abnormality increases with increasing symptom severity. Hence, the relationship between the glutamate/GABA ratio and autism and schizophrenia spectrum traits in an unmedicated, subclinical population was investigated.MethodsA total of 37 adults (19 female, 18 male) aged 18-38 years completed the Autism Spectrum Quotient (AQ) and Schizotypal Personality Questionnaire (SPQ), and participated in the resting state proton magnetic resonance spectroscopy study in which sequences specific for quantification of glutamate and GABA+ concentration were applied to a right and left superior temporal voxel.ResultsThere were significant, moderate, positive relationships between right superior temporal glutamate/GABA+ ratio and AQ, SPQ and AQ+SPQ total scores (p<0.05), SPQ subscales Social Anxiety, No Close Friend, Constricted Affect, Odd Behaviour, Odd Speech, Ideas of Reference and Suspiciousness, and AQ subscales Social Skills, Communication and Attention Switching (p<0.05); increased glutamate/GABA+ coinciding with higher scores on these subscales. Only the relationships between glutamate/GABA+ ratio and Social Anxiety, Constricted Affect, Social Skills and Communication survived multiple comparison correction (p< 0.004). Left superior temporal glutamate/GABA+ ratio reduced with increasing restricted imagination (p<0.05).ConclusionThese findings demonstrate evidence for an association between excitatory/inhibitory neurotransmitter concentrations and symptoms that are shared between the autism and schizophrenia spectra.
Highlights
Symptoms within many psychiatric disorders exist on a spectrum from clinical pathology to subclinical personality traits
A total of 37 adults (19 female, 18 male) aged 18-38 years completed the Autism Spectrum Quotient (AQ) and Schizotypal Personality Questionnaire (SPQ), and participated in the resting state proton magnetic resonance spectroscopy study in which sequences specific for quantification of glutamate and glutamate and inhibitory γ-aminobutyric acid (GABA)+ concentration were applied to a right and left superior temporal voxel
Left superior temporal glutamate/GABA+ ratio reduced with increasing restricted imagination (p
Summary
Symptoms within many psychiatric disorders exist on a spectrum from clinical pathology to subclinical personality traits. Autism and schizophrenia are among these spectrum disorders, with trait phenotypes reliably identified in the high functioning population using psychometric instruments such as the Autism Spectrum Quotient (AQ [1]) and the Schizotypal Personality Questionnaire (SPQ [2]) Subscales within these instruments were intended to reflect specific symptoms of the respective disorder, insofar as social and communication deficits, and restricted and repetitive interests and behaviours are measured by the AQ, and the positive, negative and disorganized dimensions of schizophrenia spectrum disorders are measured by the SPQ. Higher scores on the AQ subscales Social Skills and Communication have been closely related to higher scores on the SPQ subscales Constricted Affect, Social Anxiety and No Close Friends [3, 5,6,7], as well as the disorganized subscales [10] This overlap questions the capacity of the AQ and the SPQ to discriminate between similarities across the two spectra, and instead indicates that a shared symptom phenotype exists. The relationship between the glutamate/GABA ratio and autism and schizophrenia spectrum traits in an unmedicated, subclinical population was investigated
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