Hippocampus and amygdala volumes in children and young adults at high-risk of schizophrenia: research synthesis

Background: Studies have reported hippocampal and amygdala volume abnormalities in schizophrenic patients. It is necessary to explore the potential for these structures as early disease markers in subjects at high risk (HR) of schizophrenia.

Methods: We performed a review of 29 magnetic resonance imaging (MRI) studies measuring hippocampal and amygdala volumes in subjects at HR for schizophrenia. We reclassified subjects in 3 new HR categories: presence of only risk symptoms (psychotic moderate symptoms), presence of only risk factors (genetic, developmental or environmental), and presence of combined risk symptoms/factors.

Results: Hippocampal volume reductions were detected in subjects with first episode (FE) of psychosis, in all young adults and in adolescents at HR of schizophrenia. The loss of tissue was mainly located in the posterior part of hippocampus and the right side seems more vulnerable in young adults with only risk symptoms. Instead, the anterior sector seems more involved in HR subjects with genetic risks. Abnormal amygdala volumes were found in FE subjects, in children with combined risk symptoms/factors and in older subjects using different inclusion criteria, but not in young adults.

Conclusion: Hippocampal and amygdala abnormalities may be present before schizophrenia onset. Further studies should be conducted to clarify whether these abnormalities are causally or effectually related to neurodevelopment. Shape analysis could clarify the impact of environmental, genetic, and developmental factors on the medial temporal structures during the evolution of this disease.