title: White matter differences in monozygotic twins discordant or concordant for obsessive-compulsive symptoms: a combined diffusion tensor imaging/voxel-based morphometry study.
abstract: BACKGROUND
  Neuroimaging studies of obsessive-compulsive disorder (OCD) patients point to deficits in cortico-striato-thalamo-cortical circuits that might include changes in white matter. The contribution of environmental and genetic factors to the various OCD-related changes in brain structures remains to be established.
  
  
  METHODS
  White matter structures were analyzed in 140 subjects with both diffusion tensor imaging and voxel-based morphometry. We studied 20 monozygotic twin pairs discordant for obsessive-compulsive symptoms (OCS) to detect the effects of environmental risk factors for obsessive-compulsive (OC) symptomatology. Furthermore, we compared 28 monozygotic twin pairs concordant for low OCS scores with 23 twin pairs concordant for high OCS scores to detect the effects of genetic risk factors for OC symptomatology.
  
  
  RESULTS
  Discordant pair analysis showed that the environmental risk was associated with an increase in dorsolateral-prefrontal white matter. Analysis of concordant pairs showed that the genetic risk was associated with a decrease in inferior frontal white matter. Various white matter tracts showed opposite effects of environmental and genetic risk factors (e.g., right medial frontal, left parietal, and right middle temporal), illustrating the need for designs that separate these classes of risk factors.
  
  
  CONCLUSIONS
  Different white matter regions were affected by environmental and genetic risk factors for OC symptomatology, but both classes of risk factors might, in aggregate, create an imbalance between the indirect loop of the cortico-striato-thalamo-cortical network (to the dorsolateral-prefrontal region)-important for inhibition and switching between behaviors-and the direct loop (involving the inferior frontal region) that contributes to the initiation and continuation of behaviors.
authors.affiliation: Department of Biological Psychology, VU University, Amsterdam, the Netherlands. a.den.braber@psy.vu.nl
authors.forename: Anouk
authors.initials: A
authors.lastname: den Braber
authors.forename: Dennis
authors.initials: D
authors.lastname: van 't Ent
authors.forename: Dorret I
authors.initials: DI
authors.lastname: Boomsma
authors.forename: Danielle C
authors.initials: DC
authors.lastname: Cath
authors.forename: Dick J
authors.initials: DJ
authors.lastname: Veltman
authors.forename: Paul M
authors.initials: PM
authors.lastname: Thompson
authors.forename: Eco J C
authors.initials: EJ
authors.lastname: de Geus
mesh_terms: D000328:Adult; D001921:Brain / Q000473:pathology*; D001931:Brain Mapping; D056324:Diffusion Tensor Imaging / Q000379:methods; D004200:Diseases in Twins / Q000175:diagnosis; D004777:Environment; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D009771:Obsessive-Compulsive Disorder / Q000175:diagnosis* / Q000235:genetics*; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014430:Twins, Monozygotic; D055815:Young Adult