title: Genetic contributions to changes of fiber tracts of ventral visual stream in 22q11.2 deletion syndrome.
abstract: Patients with 22q11.2 deletion syndrome (22q11.2DS) represent a population at high risk for developing schizophrenia, as well as learning disabilities. Deficits in visuo-spatial memory are thought to underlie some of the cognitive disabilities. Neuronal substrates of visuo-spatial memory include the inferior fronto-occipital fasciculus (IFOF) and the inferior longitudinal fasciculus (ILF), two tracts that comprise the ventral visual stream. Diffusion Tensor Magnetic Resonance Imaging (DT-MRI) is an established method to evaluate white matter (WM) connections in vivo. DT-MRI scans of nine 22q11.2DS young adults and nine matched healthy subjects were acquired. Tractography of the IFOF and the ILF was performed. DT-MRI indices, including Fractional anisotropy (FA, measure of WM changes), axial diffusivity (AD, measure of axonal changes) and radial diffusivity (RD, measure of myelin changes) of each of the tracts and each group were measured and compared. The 22q11.2DS group showed statistically significant reductions of FA in IFOF in the left hemisphere. Additionally, reductions of AD were found in the IFOF and the ILF in both hemispheres. These findings might be the consequence of axonal changes, which is possibly due to fewer, thinner, or less organized fibers. No changes in RD were detected in any of the tracts delineated, which is in contrast to findings in schizophrenia patients where increases in RD are believed to be indicative of demyelination. We conclude that reduced axonal changes may be key to understanding the underlying pathology of WM leading to the visuo-spatial phenotype in 22q11.2DS.
authors.affiliation: Psychiatry Neuroimaging Laboratory, Department of Psychiatry, Brigham and Women's Hospital, Harvard Medical School, 1249 Boylston Street, Boston, MA, 02115, USA, zora@bwh.harvard.edu.
authors.forename: Zora
authors.initials: Z
authors.lastname: Kikinis
authors.forename: Nikos
authors.initials: N
authors.lastname: Makris
authors.forename: Christine T
authors.initials: CT
authors.lastname: Finn
authors.forename: Sylvain
authors.initials: S
authors.lastname: Bouix
authors.forename: Diandra
authors.initials: D
authors.lastname: Lucia
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Coleman
authors.forename: Erica
authors.initials: E
authors.lastname: Tworog-Dube
authors.forename: Ron
authors.initials: R
authors.lastname: Kikinis
authors.forename: Raju
authors.initials: R
authors.lastname: Kucherlapati
authors.forename: Martha E
authors.initials: ME
authors.lastname: Shenton
authors.forename: Marek
authors.initials: M
authors.lastname: Kubicki
mesh_terms: D000328:Adult; D003711:Demyelinating Diseases / Q000235:genetics* / Q000473:pathology*; D004062:DiGeorge Syndrome / Q000235:genetics* / Q000473:pathology*; D056324:Diffusion Tensor Imaging; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D014795:Visual Pathways / Q000473:pathology* / Q000503:physiopathology*