M162. FRONTO-STRIATAL-THALAMIC CIRCUITRY ABNORMALITIES IN WHITE MATTER TRACTS IN INDIVIDUALS WITH 22Q11.2 DELETION SYNDROME
Authors: Heller Carina , Steinmann Saskia , Makris Nikos , Charron Lily , Antshel Kevin M , Fremont Wanda , Coman Ioana L , Schweinberger Stefan R , Weiß Thomas , Bouix Sylvain , Kubicki Marek , Kates Wendy , Shenton Martha , Levitt James , Kikinis Zora 
Published: May 2020

Abstract

Background
Cognitive decline is considered a fundamental component in schizophrenia. Abnormalities in fronto-striatal-thalamic (FST) sub-circuits are present in schizophrenia and are associated with cognitive impairments. However, it remains unknown whether abnormalities in FST sub-circuits are present before psychosis onset. This may be elucidated by investigating young adults with 22q11.2 deletion syndrome (22q11DS), of whom 30% will develop schizophrenia in adulthood. In 22q11DS, cognitive decline, most pronounced in Verbal IQ (VIQ), precedes the onset of psychosis and those who develop psychosis diverge more strongly from a typical cognitive trajectory. Based on these findings, studies of young adults with 22q11DS without overt psychosis but with prodromal symptoms may increase our understanding of cognitive manifestations and early pathology in FST sub-circuits in schizophrenia. Here we examined white matter (WM) tracts in FST sub-circuits, especially those involving dorsolateral (DLPFC) and ventrolateral prefrontal cortex (VLPFC), and their associations with VIQ in young adults with 22q11DS with and without prodromal symptoms.

Methods
We compared Fractional Anisotropy (FA), Axial Diffusivity (AD), and Radial Diffusivity (RD) in tracts of the FST sub-circuits in 21 individuals with 22q11DS with prodromal symptoms (age: M=21.43) and 30 individuals without prodromal symptoms (age: M=20.73) to 30 healthy controls (age: M=20.89). Two-tensor tractography was applied to reconstruct WM fiber tracts of the whole brain, followed by applying the White Matter Query Language (WMQL) method to select tracts between striatum and thalamus, with the rostral middle frontal gyrus (rMFG) and inferior frontal gyrus (IFG), representing DLPFC and VLPFC. This yielded four tracts of interest: thalamus-rMFG, thalamus-IFG, striatum-rMFG, and striatum-IFG tracts. Additionally, correlations between the dMRI measures and scores on VIQ were performed.

Results
FA was significantly increased, while RD was significantly decreased in most WM tracts in both 22q11DS groups when compared to healthy controls. In the whole 22q11DS group, VIQ correlated negatively with FA in the right thalamus-IFG tract (r=-0.336, p=.018), while RD correlated positively with VIQ in the right thalamus-IFG tract (r=0.290, p=.043) in individuals with 22q11DS, such that increased FA and decreased RD were associated with a lower VIQ. We followed up on the results in individuals with 22q11DS with prodromal symptoms to determine whether the presence of prodromal symptoms drove the correlations. VIQ correlated significantly with FA (r=-0.491, p=0.024, FDR-adjusted=0.048) and significantly at trend level with RD (r=0.487, p=0.025, FDR-adjusted=0.050) in the right thalamus-IFG tract in individuals with 22q11DS with prodromal symptoms.

Discussion
Microstructural abnormalities in brain WM tracts connecting the thalamus and the striatum with prefrontal cortices are present in young adults with 22q11DS with and without prodromal symptoms compared to healthy controls. These abnormalities are associated with the individuals’ cognitive performance in VIQ in individuals with 22q11DS with prodromal symptoms and therefore emphasize the potential involvement of the FST sub-circuits in schizophrenia. While changes in FST circuitry have been reported in patients with schizophrenia, we observed that changes in FST circuitry are also present in young adults with 22q11DS at risk for but without psychotic symptoms. Our results suggest that psychosis onset in 22q11DS may be associated with a complex pattern of WM alterations. Furthermore, cognitive abnormalities, especially in VIQ, present an important preclinical risk factor for psychosis in 22q11DS.